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At a local bar they had a game machine, and if you got a high score on any of the games, your tab for the evening was free.

One of the games was a "spot the differences" between two pictures with an ever decreasing timer for each round. Using this trick I was able to easily surpass the high score, and garner a crowd watching me perform this mind numbing feat.

Probably my peak fame right there.

>Probably my peak fame right there.

My son and I always make jokes about everyone's 5 minutes of fame. Some random person on the jumbotron at a sporting event "Yup, there's his moment, it's over now."

At least yours got you something ;)

I once accidentally dropped a glass that was about half full of water and I somehow managed to catch it with the side of my foot without spilling any.

Sadly no one saw this 'feet'.

I did that once in my dorm room - then I dropped the glass and promptly stood on it. I actually gave myself a round of applause before going to get my foot sewn back together.

One of my dad's sayings when somebody in a film delivered a line and then disappeared was "6 months rehearsal for that."

I envision happy families watching the end credits for Dad's name as Third Assistant Caterer on a big budget film.

This is totally the case! The first time I was credited in a big production[0] I totally made my family watch the credits. Luckily, my name (Daniel Kvick) was quite close to the top.

Unfortunately, in the next game I made them watch the credits[1] for my son's name in Production Babies. It is right at the end and the wait was embarrassingly long.

[0] https://www.mobygames.com/game/75645/need-for-speed/credits/... [1] https://www.mobygames.com/game/98129/need-for-speed-payback/...

And getting pissed off because Netflix minimizes it into the corner to already try to push some other show on you.

Couldn’t be worse then a YouTube short that has writing in the video but is covered by the subscribe button and some description of the video you wish were not there

I now always stay around in the movie theater to see who the sysadmins were that worked on the film, for solidarity reasons. :-) Pretty much all the movies these days have them, which I would have never imagined would be the case back in the '80s when I started this career path.

Huh I’ve never noticed a sysad credit in a credits roll. Are they labeled as something else?

It depends, sometimes yes sometimes no. Toy Story 2 says "systems administrators & support" for example: https://youtu.be/4rL_4Xqak1Y?si=R2ykfdSarIjjGDZP&t=288

Best Boy Grip, the assistant to the Key Grip

Thank you for putting that image in my mind, it brought a smile to my face.

The swordsman in Indiana Jones comes to mind.

The guy famously trained for months for the fight scene and a tired Harrison Ford just pulled out the gun and shot him. Everybody thought it was hilarious and that became the scene.

I remember hearing/seeing that "he had the shits" that day, and wanted to wrap-up the scene so he can go recover/rest.

https://screenrant.com/indiana-jones-swordsman-shoot-raiders...

"It sounds wrong to say one should thank Ford’s sickness for one of the most iconic scenes, but Raiders of the Lost Ark is definitely better off for it."

https://screenrant.com/indiana-jones-raiders-lost-ark-gun-kn...

"A much more elaborate fight scene was planned, but Ford developed dysentery while filming in Morocco..."

A funny quip from mst3k was “their whole family probably gathered in front of the tv to watch them deliver that 1 line.”

That is a very Dad thing to say.

You may or may not be aware that Andy Warhol famously quipped that, "in the future, everyone will be famous for 15 minutes," back in the late 1960s. As media has gotten to be ever more ubiquitous and the cost of entry lower, he was clearly onto something decades before the internet!

And then there’s Banksy’s “in the future, everyone will be anonymous for 15 minutes“. For pretty much the same reasons you stated above, I assume.

is that how long it takes before a newborn is given their SSN?

A few weeks, as I recall.

In a modern hospital, depending on how healthy a baby is, it might get as many as 15 minutes before the not-removable-except-by-cutting RFID-enabled tag is attached to the wrist or ankle and it becomes part of the hospital inventory and the movements are tracked religiously. They are deathly afraid of accidentally mixing up babies between parents (with a side of worry about them getting stolen). Each of my kids were born at a hospital that averaged a delivery every 15-20 minutes. A nurse may see 50 deliveries in a shift and keeping track is going to be a challenge.

That’s true, I just meant SSN. Newborns are not anonymous by design.

To update this excellent quote to 2025, change minutes to seconds and you just described TikTok.

Yeah, I was thinking that the while modern social media has made the "cost of entry lower," and everyone can theoretically reach more people than ever, it's hard to even describe most of it as "fame" anymore. I mean, does content even "go viral" anymore, with users subdivided into the tiniest niche communities or audiences? Even if things get wider traction for a while, there's so much competition with so much other content that everything seems to get quickly drowned out and then can't even be found again later through search.

There’s a saying on twitter that every day there is a main character and the goal of twitter is to not be it.

Lol once I 3d printed my daughter a “Rocktopus”. It was a model of Dwane Johnson “the Rock” head with articulating octopus arms a cool 3d print that was funny. Anyways she took it and painted it all up and then glued on fake eye lashes and makeup on it. She then made a video to TikTok or snap I forget and it went viral getting like a million views. I could see that made her happy like a dopamine hit so told her that it was fun but to just be careful and that she is awesome and not to stress if random people on the internet don’t validate her feelings. She has me beat though I think my highest upvoted post was like 15k or so on reddit for something satirical and dumb. Feels good in the moment.

Totally indulging in this side discussion: I remember thinking in high school and college that fame was the end-all of life, telling people that my goal was to have my own Wikipedia page. I saw it as something like the combination of being a "cool kid" (but for, you know, the whole of society instead of just one's school) and a sort of immortality.

Anyway, over the last couple of decades as an adult, besides realizing the obvious - how terribly shallow that is, and missing so much of what's really good in life - I've realized how fleeting fame seems to be even for the truly famous. Even looking over the list of US Presidents (never mind lesser political figures like VPs, cabinet members, congressmen, etc.) as someone who has always been interested in history, I look at some names and think, "who?" or "I've heard the name, but know nothing about him." I mean, of course you can still read about them, but that even a US President can be largely forgotten as a household name within 250 years is really a stunning thing to think about; they are ultimately no more immortal than someone who only has their name in a genealogy database or on a grave marker.

I think the desire for fame isn't an inherently bad thing.

> He was the man most gracious and fair-minded, > Kindest to his people and keenest to win fame.

Those are the last lines of Beowulf. A man who won great fame among his people by slaying monsters and dragons. It's telling that the final line of the poem ends with his most dominant trait, "and keenest to win fame." Wanting fame is not wrong, and is far from shallow. The question is, "fame for what?" Regardless of whether you think Beowulf existed or not, it's telling that for a whole culture that the most important characteristic of a great man in one of their great poemsis "keenness to win fame," almost as a wink, with the bard saying "and if you want to be sung like this hero, you must desire fame just as keenly, and so do great deeds."

"True glory consists in doing what deserves to be written, in writing what deserves to be read, and in so living as to make the world happier and better for our living in it."

Length of remembrance aside, the idea of fame as immortality has always confused me on different grounds. It's not how fame works: we remember factoids, not people. It's a bit different if the fame is a work of art, but then the thing with immortality (sort of) is the art, not the person that made it. I might remember 7 things about Teddy Roosevelt, which are admittedly very cool and impressive things, but those things do nothing to represent the complex individual he actually was.

This may be something I'm making up, but I have the feeling that the fame = immortality concept came out of legacy: people wanting to create a family that continues on after themselves (and is rich, powerful, etc). Which makes sense, because then we're talking about a logical extension of the reproductive instinct. But in the modern world even that seems unreachable to me: we're so utterly different from our grandparents that we might as well be aliens, and the same will probably hold true for our own grandchildren.

I guess all that puts me in the Mike Tyson school of thought on legacy: "We're just dead. We're dust. We're absolutely nothing."

You are deacribing here are kinds of thoughts and how they manifest in generations. one is that brings things into physical existence(fame via achievement, children).

Another is that which is kind of intangible and describes the person(again not personal details but what they think about the self and ideas), like an autobiography, but still is very hard to get at: it's like they say Being in someones shoes.

It's impossible to understand both of the above kinds of thoughts, in general, because conscious thought is utterly temporary and highly subjective. And more so for the second kind of thought above for most people it is true that, their complex self is meaningless to others.

It's likely why you mentioned you feel disassociated from what your parents/grandparents thought.

You make good points. When I looked up the word "immortality" in Merriam Webster while writing my first comment, I found it interesting that one of the definitions was actually "lasting fame."

> we remember factoids... I might remember 7 things about Teddy Roosevelt... but those things do nothing to represent the complex individual he actually was.

I've thought this before when looking at Wikipedia pages. Especially for less famous people with thin pages, they'll cite just a handful of news articles or press releases in which the person appeared. If there were a page like that for me, or the people that I know best, the collection of factoids would be a laughably inaccurate reflection of who we really are. Someone told me that it's important to write an autobiography for this reason.

My grandfather wrote a short autobiography, just for his immediate family. It's a really nice thing to have.

We are all doomed to be forgotten.

Even if you are remembered briefly, what’s remembered isn’t you it’s just some vague representation of you that will fade over time.

Some famous Roman emperor might have said something similar 2000 years ago for all I know but I forget his name. :P

Absolutely not, at least if you don’t think in terms of personal fame but impact you have on the people you live with. It’s something that becomes super apparent when you have kids. You pass on so much and that will live on forever, in a million remixes. I love that idea as it gives a lot of meaning and purpose even on the small little moments and things in life.

It’s a know phenomenon. A friend of mine had a reasonably important public office position. Always on the phone, constantly demanded, giving interviews, etc. The first few months after a change in administration were a great relief. A year after being let go and he was devastated. No one called, knew or cared who he was. There’s probably a name for this syndrome.

A kenyan politician once wrote about it. They even thought their phone had an issue because when they were in office they would receive an average of 30 phone calls an hour, once they left it was zero in a day till they though the phone had gotten spoilt

https://nation.africa/kenya/blogs-opinion/blogs/dot9/ndemo/t...

Except that if you become curious about, say, Benjamin Harrison you can go look up his Wikipedia page and I presume find one or more books about him. The person who is just listed somewhere such as a genealogy database is just a name, unless you choose to do an elaborate and expensive research project on them to figure out who they were and what they did.

That's just because US presidents are not very important.

Humanity will not forget Newton, Einstein, Shannon and Crick. And up to a point, trying to do what they did, discover new things about the universe is not an unhealthy goal.

We do not know who invented zero. Or who identified earth to be a sphere. Or who wrote the sequence 1, 1, 2, 3, 5, 8 ... . We just pick a name and associate them to our liking.

So when another colonizer comes up, we will have newer people associated with these. Hope it does not happen. But history does say so.

Humanity as a whole, perhaps not; but that is not the same as what cultures within do, and cultures have many ways to erase or diminish outsiders — and everyone's an outsider to some group.

Newton, Leibniz; Einstein, Lorenz and Riemann; Shannon, Kolmogorov; Crick, Franklin.

When the context is, to quote the parent comment:

> I look at some names and think, "who?" or "I've heard the name, but know nothing about him." I mean, of course you can still read about them, but that even a US President can be largely forgotten as a household name within 250 years is really a stunning thing to think about

I suspect only Newton and Einstein are even household names. I'd be very surprised if the average person has heard of even one of Lorenz, Riemann, Shannon, Kolmogorov, or Crick, even today, and my guess is that Franklin would probably be assumed to be an associate of either Roosevelt or Benjamin, given the widely claimed but inconsistently cited survey that 12% of Americans think Joan of Arc was Noah's wife.

And Crick's other famous research associate was Watson; I wonder how many times people got him mixed up with the fictional character, or briefly for the IBM computer.

I'll be honest: I didn't know who Crick was. Now that you've associated Crick and Watson, I was able to find the appropriate Wikipedia page. And yeah, this is not the Watson that I was expecting.

Regarding Shannon, I've read one of his biographies (A Mind at Play), but outside of my circle of friends with CS degrees I don't think anyone I know would know his name.

To your point, I was thinking that this might only be stunning for someone with a modern view of the US Presidency. I understand that the powers of the office and the election campaigns for it were quite different in earlier eras.

However, I remember someone who went to MIT observing the same thing about the names of the great scientists and philosophers etched onto the buildings. He noted that he only knew what a few of them did.

IMHO one should only desire to become Confucius level famous. The kind where you don't need validation to know you've done something interesting.

I think it depends a bit more on what you do, than your role. As you mentioned, being President of the USA is not even enough.

And yet you might be able to list some Roman Emperors, for good or bad (Cesar, Augustus) or even politicians (Cicero, may e Seneca) after 2000 years.

I suspect that Washington might still be a household name 2,000 years from now like that. Other past US Presidents, I agree, no.

As an aside, I'm really hoping that Trump doesn't do anything notable enough to somehow be like that. I fear that he might be more driven to do so than any past US President.

I can't overlap the images to save my life - they get like halfway there and that's it...

There is a way to help yourself.

Put the pair of images in front of your eyes.

Bring your finger between your face and the image.

Now look at your finger.

Move your finger back and forth.

While doing this, notice that at a particular distance, the images in background will perfectly overlap each other.

That's your moment.

Pull out your finger and look at that image.

---

Should take lot less tries to learn doing it without finger. I have taught cross eye to my siblings and cousins using this method. But if you always need finger to focus it's fine.

I knew about this cross-eyed trick, I've tried it with a finger too, I just cannot do it. I've only ever succeeded in one "magic eye" picture in my life as well.

I have otherwise good vision, I can read small text from farther than most people (I didn't realize not everyone could read all the small letters on an eye test), I don't have a problem seeing things up close either, etc. but I lack the ability to properly cross my eyes for some reason.

It's too bad because I've spent a decent amount of time at bars with those spot the difference machines lol

Another method is parallel eye though it's bit more complicated than the finger.

Zoom the images in front of your eyes so that they are little less than same width as your eyes.

Try to look behind/beyond the image, as in let your eyes loose/relax. Don't stare at the images instead see in that direction as if you are day dreaming.

Images will overlap at one point. If they don't completely perfectly overlap, reduce the zoom.

Once they overlap, focus the overlapped image.

---

Method 2: Use kitchen towel rolls

After putting those images in front of you, make a binocular out of used kitchen rolls.

Point each roll to each image.

There you go.

To me, it's no harder than "snapping" to the central image when wearing VR glasses like the Vitures. What works for me is telling myself that the central image is further back than the two slightly unfocused images either side. Just keep telling yourself "it's further away, and it's the real one. Those two are fake." As soon as it clears up just a little, I then allow my gaze to wander around the image. It's extremely important to try this on a real monitor because small movements to the phone in your hand might get in the way. Or in my case, I'm longsighted in one eye, so while my left gets a clear image my right doesn't. I have to use a large image on a real monitor at least 2 feet away.

When I was six, some older kid showed me this trick, but I could never really cross my eyes. These days, I wear glasses, so I guess no new superpowers for me.

Does it not work with glasses?

it does work with glasses

I tried, this, and I can get it to overlap in the background, but as soon as I take my finger away, I lose it.

I was having this problem as well, but I kept trying, and then I got it. I found the finger trick was useful to initially sort of calibrate the focal distance but overall didn't really help me that much.

Here is what worked for me. I used my laptop, zoomed in a bit on the images and brought the screen fairly close to my face. I ensured that the image was crisp using each eye (I also have astigmatism, and I probably also need reading glasses, but there is a sweet spot where both eyes have good focus, and I ensured I was there.) While crossing my eyes a bit, I start to see a third image in the center of the two images, but it's either out of focus (like two overlapping images), or it's very thin, like it's not the full image. I relax and keep my attention on this imperfect image and try to focus on it without trying too hard. Using this approach the image suddenly comes into focus and I no longer have to try to keep it there.

I feel like the key might be to notice the very beginning of the desired image in the center and then to try and focus on it, but in a bit of a relaxed way.

Incidentally when it works it is extremely weird! The other images essentially disappear and it's like you've travelled to another dimension.

Ditto the focus distance. I just saw the eye doctor and found it I have thickening of my left lens (giving me great vision real close up) and the start of longsightedness in my right eye. The combination means that my sweet spot is far enough away that I need to use a monitor.

You may have a very slightly 'lazy eye' (I do) - it can be a lot less extreme (not at all noticeable to others) than the pointing-completely-different-directions that people imagine, and iirc is highly correlated with astigmatism.

Optician used to tell me to work the muscle by following my finger to my nose, trying to maintain a single image. At a certain point it will snap into two - the 'lazy' eye has given up and drifted slightly - the goal is to get the finger as close as possible. Obviously if you get very close or all the way, that's 'cross-eyed', but I just can't do it.

Same, and I had no idea it was correlated with astigmatism! That does explain my prescription

I’m also unable to do this for whatever reason but using a stereoscope works.

The finger trick did it for me. As mentioned elsewhere, I used to do this academically (looking at protein structures), but I couldn't easily get back in the groove here without the finger.

It's like

https://triaxes.com/docs/3DTheory-en/522ParallelCrosseyedvie...

which some people struggle with, somebody posted a

https://en.wikipedia.org/wiki/Autostereogram

to HN yesterday which some people get and others don't. (That's different from the "cross-eyed stereogram" because one of them involves having two images and the other one has one image with two images hidden in it)

I can understand why it's hard for some. I've landed on that wiki page a while ago and couldn't figure it out. Then found a similar thing on an itch.io page that was easier for me to figure out.

In these later examples (starting with the easy puzzle of the OP, and your 3d examples), I find that I do the process in two stages.

Unfocus my sight until the third image shows up in the middle at the correct size (as a blurry mess). Then try to focus the center image.

What's more a lot of people (maybe 20%) don't benefit from things like

https://www.reald.com/

which is one reason why stereo movies have struggled. (That plus some people get sick... Having both a flat and 3-d movie in two different theaters comes across as money grubbing to the consumer but it is really a money sink to the theater.)

Yeah that's me. I lack stereoscopic vision so such tricks or 3d glasses etc do not work.

Really interesting. I never knew how those old magic eye images work.

It makes me wonder if the wall-eyed version could be useful for eye health.

I've often heard when doing computer work, you should focus on something 20 meters away for 20 seconds, every 20 minutes.

Doing a wall-eyed magic eye seems like the same thing physically, your focal point is much further away.

Would be cool to have some software that lets you overlap two coding windows, so you have a 3d terminal.

I have a big problem crossing my eyes too while having no problem with the parallel view way seeing stereograms. I am actually going to stop trying as my eyes started to hurt.

For me, what's difficult is holding my right eye closed without my left eye drifting to look at my nose. My right eye's good, I can move it and focus on anything within my (now peripheral-limited) view... but the left is wonky. I think I learned how to wink (and hold it) with the right really early, by age 3 or 4, but the other side I never tried until I was pre-teen... some sort of muscle atrophy?

You can also tell if your head's level, just by crossing your eyes. If the two images are diagonal to each other, then your eyes/head aren't level. I have no idea what the possible use for that would be.

Which one makes things become bigger? I learned that one first and then later figured out the one that makes the mixed image smaller (cross eyed I think?). Now I cannot do the big one anymore.

That was me at first.

I think the "cross eyed" phrase is a bit ambiguous.

What I ended up with (I think) is a focal point not closer than the screen but farther than it. My eyes didn't want to do it at first but then they did.

What is weird about it is the focusing and focal point are out of sync --- my brain can do it but the weird feeling is one of "gosh, this thing is a lot closer than it should be" where "should be" is based on focal point, and "is a lot closer" is based on focus.

Don't want to do this too much, feels like I could easily decalibrate my brain for real life lol.

That focus-farther-than-the-page works (for most people) as long as the distance between the (center of each of the) two images on the page is smaller than your interpupillary distance. In this case the left eye will see the left image, the right eye the right image, in the overlaid resolved image.

For most people, having the images resolve in front of the plane of the page such that in resolved overlaid image the right eye sees the left image, and the left eye sees the right image, will work ... and it can work even if the images are farther apart than the interpupillary distance.

Thanks, that is nicely explained --- you finished the thinking I had only started!

Are the eyes mechanically capable of pointing outward (so the interpupillary distance is not longer a constraint)? If so, is the problem then neurological not mechanical (brain doesn't want to send signal so they do that)?

This helped me more than any other comment here, but I've still not got them fully overlapping. (Probably just a matter of practice/trials at this point, to be fair.)

Here's another trick: open the image in a browser, then zoom out. The smaller the image (up to a point and you can find a sweet spot) the easier it is to get them to overlap. Once you've got it, slowly zoom in a bit at a time, re-acquiring the overlap at each stage.

I spent far too much time as a twenty-something generating autostereograms, which seems to have trained my eyes. I was able to "cross" the images on this page very quickly.

NB autostereograms require you to move your eyes away from each other, the opposite of crossing them. To put it another way, crossing your eyes is what your eyes do when you're looking at something close to you, while the opposite is when you're looking far away.

Which is why for ASGs people advise you to look past the picture. Or why you bring the pic close to your eyes (so close that you basically have no choice but to look beyond the picture)

Ever since I was a child addicted to the "magic eye" stereogram books, I've always diverged (not crossed) my eyes for spot-the-difference puzzles.

Also, if you're doing it on a piece of paper, hold a pen in each hand spaced right so you see the middle (3rd) hand in the middle combined image, and move both hands in sync to circle all the differences. Kind of a cool way to point them out to someone else.

The difficult puzzle took me about 10 seconds here since I was looking for more than one difference. I saw the first difference in about 1 second.

You can easily generate inverted ones that require crossing your eyes to appear properly, but they don't look as nice since they pop out instead of going into the screen/book.

Is that the crossy-eye porn?

Better known as Magic Eye, but yes.

Don’t CROSS them. Relax them, like you’re tired and can’t focus on a computer screen.

You can actually do it both ways, but which is easiest for whom is different.

Also keep the size low. If you’re having a hard time at 20cm from a 4k 30” monitor, it won’t come easy. Zoom out.

I cross them first, then slowly relax them and as the two pupils start to move slowly back out I tell myself that the middle image is further away and "real".

It helps me to see the depth and then properly focus to cross them very slightly to start, then as I see the image my eyes adjust to pull it in focus properly.

Yep, I didn't need to fully cross them. Which is good, because that is painful.

There are two methods, either you cross them either you do like you’re describing.

Same as in autostereogram, the trick is to look to the distance. Close your eyes and imagine a mountain far away or some distant object, notice how your eyes adjust to see it. Open your eyes and try to look at this imaginary mountain while the image is in front of you. When you see the third Image, treat it as if its a distant 3d object somewhere on the horizon.

When I brought an early autostereogram in to school in the early '90s my high school Physics teacher refused to try it as he thought it sounded impossible. He thought we were all in on it as we 'got it' one after another.

I have just figured that using kitchen towel rolls as a binoculars is the easiest way to do a parallel eye on these kind of images.

Try that.

Hold the rolls like binoculars where right roll is pointing at right image and left is at left image.

It's like a DIY VR headset where your brain/eyes only gets two same looking things to focus. No outside noise.

That happened to me too but I persisted and eventually succeeded. I think I needed to cross my eyes slightly more than I was initially. I have been diagnosed with a minor eye convergence issue which makes it difficult to focus on near field objects in motion -- gaining this superpower was difficult but I did it without a headache thankfully.

What really helped me was doing some sessions with an Orthoptist to reeducate my eyes. I used to see double when stressed sometimes and could never imagine to converge/cross my eyes and retain focus. With the reeducation I was able to see the Impossible one in focus after a couple tries.

I had to see an eye doctor at the hospital when I was ~7 and I got to do some exercises, but I never learned to cross my eyes, and then it was like it probably wasn't very important since I did not have to go to the doctor again and no one mentioned it so I just went on with my life and it seems overall like not being able to cross my eyes is not a huge problem. But I guess it may be connected to my complete inability to see 3D effects or figure out how to see anything in the images in the article.

Treat it like a "Magic Eye" photo and just relax your eyes to a further focus point.

When it works you get what seems like 3 images with the middle one showing the differences; you can then relax and peruse the middle image at will. I guess all the practice with SIRDS as a child probably helps.

Try on mobile, it's easier if the images are smaller.

Wow, yeah it happened immediately for me on mobile while I couldn't get past half way on my monitor. Thanks!

Same! I feel like I can get a fleeting moment and then it's gone. I swear I could cross my eyes when I was a kid - I wonder if with practice it'll come back or if I'm just old and this skill I didn't-know-I-wanted is lost

Are you crossing your eyes (focusing nearer than the object) or diverging them (focusing past it)? Diverging is a harder skill to learn.

Is diverging harder? I find it easier. Maybe it is from long ago practice on stereograms, but I'm curious if it could be due to neurological/physiological differences.

Crossing is easier because you can simply hold your finger in front of your eyes and look at that for practice.

Diverging requires you to look past the image, meaning you have nothing to really look at, which makes it difficult to figure out what your eyes are even supposed to do.

Those stereograms aren't helping much either, since they look like nothing until you get it right. With cross-eye you have instant double-vision that you just need to align.

Cross-eye also works across much larger distances, diverging fails when the images are too far apart.

It depends on the image. If the two images are too far apart then it could require your eyes to diverge, and not to just converge slightly less. That might be impossible.

Diverging is way way easier for me, but I am positive that's because of the 10's of hours (at least) that I spent staring at magic eye images as a child.

My whole life I've been doing stereograms by diverging, but I couldn't get the three images in the post (the pairs would get closer but never fully overlap), so I tried crossing based on your comment. It was way easier than diverging (obviously, since I couldn't do it otherwise), but it took me a few tries, because I think it's actually /too/ easy to cross your eyes compared to diverging - I was way overshooting when I crossed my eyes. The trick was to notice this, and then control the un-crossing until they lined up.

Diverging is definitely harder, and might be out of focus. To keep in focus I found it easier to focus on the right image and then cross my eyes, rather than staring in the center and then staring through the screen into the distance while trying to make them line up.

I used to not be able to do the "magic eye" 3d images until recently, and this trick is pretty handy.

Not even sure which one I should try :) but yes tried both to no avail. Maybe it's just not something to achieve in the first try...

For crossing just focus on your finger and then remove it.

Looking far away may be harder, and afaik it’s near impossible to look “past infinity”, iow pictures must be less wide than the distance between your eyes.

Btw these two methods aren’t equivalent in watching stereograms. If you look at one and see something but it doesn’t really make sense, then it’s probably the opposite chirality.

Personally I hate the crossing method because it makes your eyes feel strange for a while.

how I approached crossing: first practice just crossing your eyes and observing how every object has two images in this case and when you slowly “uncross”, they merge back into one. you can use anything in your surroundings.

then for the stereogram you do the same, observe the out of focus edges of the left and right pictures, then slowly uncross until left and right image occupy the same spot as though they were the same object. now its out of focus, but one (ok, actually three, because there were two, you “doubled” that by crossing, then merged two of them. but ignore the other two and focus on the merged pair)

sometimes you will merge images of the same picture, in this case you are just back at your normal vision, repeat :)

then you try to keep them overlapped and focus the vision, try to “believe” that you are really looking at a single object.

If you mean literally you can only bring them half way together, try just moving twice as far away.

Works for me, I see 3 images if I try hard and the differences pop out

You might be too close to the screen.

Yeah, me either. My eyes really resist it. And after trying it a few times it messes up my focus for a bit.

Failed to perform the technique despite multiple retries, but didn't have any issues spotting differences the normal way for all except the impossible mode - which just felt like it would be tedious.

My usual method is just to brute-force linear scan from left to right, top-to-bottom. May not be elegant, but it works.

Fun fact- when I was a teenager, my friends and I set up a stand in a local mall selling those “magic eye”posters. We made bank for a few months. But, there are actually a lot of people that medically cannot use the technique, or at least for whom it is extremely difficult or less vivid. Severe astigmatism, (obviously) blindness in one or more eyes, and certain attention deficits or fidgety types often have a difficult time.

I, on the other hand, 37 years later,am basically permanently crosseyed from the experience lol. It somehow became a resting state for me from all of the practice, so I’m always doing it on any kind of repetitive patterns, and even “successfully” on random ones which does some really weird stuff in your visual cortex.

How bad does your astigmatism have to be? I've only ever been able to get one magic eye poster to work for me in my life, and I had no idea astigmatism had any impact until just now! I don't know if mine counts as severe, but this would explain a lot for me.

As it happens, I also can't focus on the images in TFA after crossing my eyes to get the shimmer the author refers to.

My daughter has a mild astigmatism (enough to where she needs to wear contacts) and can do the magic eyes very quickly… but maybe that’s only when she’s wearing contacts

I don’t know for sure, but it would make sense if it had to be fairly severe. If it were not enough to meaningfully distort one eye vs the other it would not seem to be detrimental. It’s only when the two images can’t be correlated any more that the problem shows up.

In my recent years I have developed some astigmatism, but I can still do them without difficulty.

Took me about 10m total to get it all the way to impossible mode. I think you can do it!

Same here. I can get the images to overlap; it feels like a stereoscopic image that lies a bit beyond the screen. But the differences don't pop out to me. I have less trouble finding them looking normally.

...except as you say, it didn't work. The "eye-cross" trick gave the answer on the impossible one in ~10 seconds.

The impossible one was sub-2-seconds for me. I had to do it over to make sure it wasn't more than one difference...

Makes you wonder if the kid he was talking about had a lazy eye or crossed eyes or something.

The impossible one was quite tricky, but I did find I was able to relax into the image and take my time. Probably took about 10 seconds.

Just got a funny visual of someone going crosseyed and focused on overcoming a challenge in front of them, with a crowd of people cheering them on.

Sadly I was never able to gain anything from this trick other than my kids admiration. Often times kids menus at restaurants will have a spot the difference and I can see everything instantly doing this. Impressive to a kid but this girl in the video was obviously doing the same thing and does not impress me.

This is my peak fame as well. I had the high score on every one of these I've played using this method. My friends were always try to figure out how we could make money doing it...

The game is usually called 'Photo Hunt'

Those Megatouch systems run Linux! Lots of fun messages to read on the credits screen or when you reboot them.

I haven't seen one in several years, but they always used to run Red Hat, based on the boot screens.

I was about to post this same exact post :)

Was the high score holder on there for a few years.

We got a magic eye book when I was maybe 6 - some time early elementary school. After learning how to do it, and also trying it by crossing my eyes to see an "inverted" image, I started doing it whenever I saw some repeating pattern IRL. It was most interesting when it was slightly uneven, for example a fence with sloppily applied vertical planks. Doing the magic eye would make it seem like some of them are closer to you than others. Eventually I tried the same on those "spot the difference" games since well it seemed kinda obvious to try, and I was blown away that it accidentally gave me that "superpower". I think that was pretty smart for a 6yo. Has only gone downhill ever since. ;-)

Now try it with various colors, some people can see "impossible" colors [0].

[0] https://preview.redd.it/yaiyf2bi9aa31.png?width=640&auto=web...

Neat, the colors only blade when perfectly aligned.

I wrote a paper about doing this using human eyes as the "repeating pattern" (either someone else's, or your own in a mirror): https://philpapers.org/archive/ALEDSK.pdf ...You can use this trick to make boring meetings or conversations mildly more amusing (but be careful not to look like a clown crossing your eyes).

If you're an expert at this, you can even do it to your own hands. Hold both hands in front of you but with one of them palm-away and one of them palm-toward you, so that they have the same shape, then cross- or parallel-view them to get an illusionary middle third hand. Walk around while focusing on the third hand and it's a seriously trippy effect.

Another "super power" application similar to OP: the ability to confirm whether or not two distant digital clocks' seconds-digits are perfectly in sync. Since they're distant, it takes time to shift one's gaze from one to the other, making it hard to confirm whether they're in sync. But cross your eyes so as to reduce the distance, and voila.

Yet another application: quickly assume the same head-tilt angle as your conversation partner. Suppose they tilt their head to the left by N degrees and you want to tilt yours the same way, how can you be sure you have the exact correct tilt? Easy: parallel-view their eyes (as described in the aforementioned paper). You will HAVE to tilt your head the same as them in order to see their "third eye" (and once you've locked on to their third eye, you can effortlessly adjust your head tilt as they do by using their third eye as the necessary guide)

If you're distant enough / the people are sitting close enough, you can stereogram two people's faces together. You usually only get fleeting moments of crispness when their heads are aligned correctly though.

Yep! If I knew someone IRL who was into this kind of stuff, I'd really love to experiment with this sort of thing and mirrors. Arrange so that you can stereogram your conversation partner's face with a mirror image of your own face (and that he can do the same with your face and a mirror image of his face). If anyone's in NYC and interested in these sorts of things, my email is in my HN profile "about".

Peak HN.

Stereogramming your colleagues eyes during boring meetings.

Ha

Edit: I accidentally did something similar by imaging the crease on an N95 mask as a smile near their nose. It made them look like ducks and I had to bite my tongue so hard to not laugh. I could not unsee it.

When I read about Gauss basically inventing Arithmetic Progression at seven years old it gives me similar vibes. What led him to see a different way in adding the numbers 1 to 100? Surely he could have visualized it on his own in an abstract manner, but I tend to wonder if he had a similar enlightening experience like yours.

Yep, this is exactly what came to mind with this "newly unlocked superpower".

I wonder if OP is aware they made a joke about the inability to use this superpower to identify a sailboat in a 90s indie movie.

Ethan Suplee is a personal hero of mine. I've been watching him in movies since clerks, and felt bad as I saw him continue to get bigger. When he started his transformation some gym bros posted it to some forums we inhabit. He didn't want to be all public about it since he'd yoyo'd before, but we cheered him on online. When I saw he'd gone public I was so happy for him. His pic now hangs in my home gym with Arnold and Ronnie.

I have never been able to see stereograms (I think because I have an eye which is far "stronger" than the other) and that movie made me feel seen.

It’s a schooner!

Wow I feel like I've never seen anyone talk about this. Doing it with fences can feel pretty magical, like the object is more "real" than other things.

Or the side of a shopping cart.

The repeating punched hole pattern on the ceiling/headliner of a '77 Suburban...

I can never do it. Always find it amusing when another kid knows how to do it.

I discovered this trick independently about a decade ago, to use cross-eyed viewing to easily spot differences between two similar images. Like you said, the parts that mismatch appear to shimmer and be unstable, making them obvious.

However, I feel eye strain from doing it, so I prefer other methods. 99% of the time, I do https://en.wikipedia.org/wiki/Blink_comparator instead, just switching between two images with zero flicker and zero displacement offset. Also with both eyes, it's easier to spot certain kinds of subtle differences like color shifts, JPEG-like compression artifacts, tiny differences in antialiased renderings, etc.

One benefit of the cross-eyed method, though, is that you can difference videos. But the use case for that is rarer than differencing images.

I'll second the blink comparator method as a simple diff checker, or when comparing two chunks of code that are structured exactly the same way but somehow behave differently. (e.g. "what's the difference between these two functions" or "how is this yaml block different from that yaml block"?)

Line them up as two tabs in the editor, flip very rapidly between the two repeatedly, and usually the difference is apparent in 5-6 flips.

To reduce eye strain, don’t cross your eyes, but relax them (so, the other way). Instantly clear and snaps together as if magnetic.

This is called “divergence” [1] and is less straining on your eyes than crossing them (“convergence” [2]) while being equally as effective spotting differences, even on video. It’s also what your eyes naturally do when you watch stereoscopic 3D with tinted glasses—the stereoscopic images are pulled out (divergence) not pushed in (convergence/cross-eyed). I’ve been doing this since I childhood. If you get good at it, you can watch side-by-side 3D videos in 3D with just your naked eye (e.g. VR). I believe there’s a reddit covering the more prurient variety of that!

[1] https://en.wikipedia.org/wiki/Vergence#Divergence

[2] https://en.wikipedia.org/wiki/Vergence#Convergence

The only problem with divergence is that you can't go too much farther out than the distance between your eyes, whereas convergence works for larger images as well.

Convergence highlighted the differences for me in all four images.

Divergence only worked for me in the cat bear image. For the others, I could see a combined image but I could not see any differences highlighted, even though I knew what to look for.

A simple trick to doing this, in case it's not clear how to do it, is to try focusing on an imaginary point behind the screen as you look at the images. You will see a third image between the two start to come into focus. Now relax your eyes and look at that image. Simple, and quite a bit more relaxing than crossing your eyes.

The only disadvantage to this method is that it seems there is a limit to how wide the middle image can be, i.e., the original images may not completely overlap.

If you do want to cross your eyes but do not know how to do it, do the opposite of the above: try to focus on an imaginary point closer to you than the screen as you look at the images. This method is far more taxing on the eyes though.

I was still unable to do this, not sure what I am doing wrong, but I can't get over the sense that I am always directing only one of my eyes. I can't move them independently.

In this case, you aren't directing your eyes, but instead looking through the object. Start with your finger about 6-8 inches from your face, and look at your screen. You'll see two fingers. Now try to look past your screen. The farther you are from the object the harder it is.

> You'll see two fingers

I don't follow this part, still. Do you mean computer screen / phone screen behind my finger which I would try to look at?

I can switch between my left and right eye when I concentrate, but I can't see both at once. I can try to rapidly switch from left to right to back, but it takes a lot of effort, and it's never the same image at once?

My right eye is dominant, I can switch to left eye if I focus hard, but I can't merge both or can I?

Edit:

I tried putting a paper between my eyes, so right eye would only see right part and left eye only left, am I supposed to see the whole image at once then combining the inputs from both eyes at the same time? Because I can only see left or right, as if my other eye was closed, even though it's not.

I'm wondering if something is wrong with me.

For me, when I look past my finger, I see two and each is sort of transparent as the image of each eye is transposed over the other. Maybe you can only see one at a time?

Finally after some time of trying I was kind of able to see 2 fingers, but I think I have some sort of condition that means I mostly have monocular vision compared to binocular vision, which most people seem to have. I am still trying to understand how different I see things from most people. But this is something I never realized.

My brain really prefers to process from only one eye at a time, it seems. I wasn't able to get further than the 2 fingers even after more than a hour of trying. E.g. I wasn't able to duplicate anything on my screen.

Weird that I only now realize this after decades of living. I wonder what impacts has it had on my depth perception etc.

The problem I have with this is that instead of the images completely overlapping they overlap a section in the middle. I can't get both images to completely overlap and am getting some eye strain from trying to force them.

By ready your comment, I just realised that this is what I’m doing instinctively, instead of crossing my eyes :o

A blink comparator would be a much better GUI tool for comparing photos (for example original vs. post-processed) than the standard "left half-right half" with a movable divider. Alas, it’s rarely used (eg. Lightroom’s compare view doesn’t have one).

Fun fact: it's a different device, but the principle is the same as the device used in the documentary Tim's Vermeer. It results in the images overlapping between your left and right eye and you simply paint until the difference goes away.

If you've done Magic Eyes, this is straightforward. Was able to get all 3 of the test images quickly.

This is with focusing beyond the screen. Focusing in front of the screen is something I am unable to do, and not for want of effort.

Also, your eyes might accidentally do this if looking at tiled patterns, e.g. wallpaper.

Relative image size (e.g. view distance) is important.

As a kid, I got a Magic Eye book and learned to see it by crossing my eyes (ie, focusing in front of the screen). I thought it was pretty interesting when I realized that I was seeing all the images inverted ("peaks" were "valleys" and vice versa) due to the way I was focusing. Alas, I never was able to see the images "correctly".

It's funny because even if you do the Magic Eye pictures "correctly" (focusing past them) you can still get funky images by going too far and locking the surrounding pattern a second time. If I remember right the first time I did this was on a heart picture (similar to [0]), which ends up looking like a big puffy W stacked on top of a slightly larger puffy W :D

[0] https://i0.wp.com/www.magiceye.com/wp-content/uploads/2018/1...

Thanks that's one of the beautifully crafted magic eye images, bring me back memories about 20 years ago when it was a craze.

I think I just locked the pattern also a third time where it looks like pillars but I’m not sure if I saw it correctly.

When I first looked at this picture I saw the W pattern and then blinked and suddenly saw the intended pattern.

When you lock on the non-intended ones it feels somehow like a secret/forbidden path you shouldn’t go, like consuming drugs.

Are you sure that's supposed to be a heart? I see the three peaks of a "W" as well -- I think it's supposed to be a tulip, no? That also matches the background theme.

Yep, well at least 98% sure anyway. But you're right, that 'second level' image does look a lot like a tulip, much better description than what I said about W's :) And of course this led me to try zooming out a bit and going for level 3+... kinda feels like I'm looking down at the top of a strangely shaped wedding cake, which would also go nicely with the flowers and heart theme. Thanks for giving me an excuse to take another look!

If you see 3 peaks you went too far - which is really easy to do on mobile. I had to be careful to go only "once deep".

The background is flowers, but the hidden image is most certainly the classic heart shape.

You can also cross your eyes the other way and make the pattern in a MagicEye pop the other way (in vs out, or vice versa)

Instead of crossing your eyes to focus in front of the image, you have to uncross them and focus on something behind the image. Put your finger about six inches in front of your face and then look at the horizon. If the horizon is in focus you should see two fingers.

Focusing behind is much easier because you can get yourself started by focusing on an actual object.

Focusing in front can be done by focusing on an actual object too? Many people e.g. put a finger between them and the picture and then remove it.

The finger method interferes more with the third image in my experience.

Same -- much harder to get them to go the other way. I'm surprised that cross-eyed random dot stereograms never took off; so much easier to do.

Yup, I loved Magic Eyes as a kid. This was easy.

Nevertheless, I was astonished that "impossible mode" literally took me only 1-2 seconds to find the missing star.

Like, I knew our vision is good at interpreting depth from images. I figured it would be all right at finding large areas of differences. I had no idea a single freaking pixel could stand out like a sore thumb.

I had trouble finding the "shiny" pixels on that one simply because the stars also had that issue - but after enlarging the image a bit more and scanning back and forth I was able to pick things out a bit better.

Now, ask me to look at my code again for a couple minutes and it might be tough but it worked :)

Maybe we are the opposite. As a kid, I could only do cross-eyed-focus-in-front-of-screen, but not "focus beyond the screen". Or a book at the time.

So I was able to see the 3D in Magic Eyes, but the 3D effect was inverted.

Today as an adult I am able to focus beyond the screen, but it's still much easier for me to do it cross-eyed.

I also got all the images in the post almost right away. But my eyeballs focused in front instead > _ <

I have a slightly lazy right eye, so this has always come naturally to me, but I will say it's considerably easier to achieve the false focal lock on printed material— something about screens, even quality ones with high refresh rates, just isn't the same.

How do you do this focusing beyond the screen!?

I'm trying so hard to make this happen. Stare really far in the distance and then move the image in front of my face on my phone. No matter the distance between my face and my phone i can't overlap the images.

Focus in front of the screen is the easy one. How do you get beyond....

You know how you can make your eyes see double when you cross your eyes a bit? Do this and you get 4 images. Combine align the center 2 images and your eyes will automatically “lock on”.

That's the focus in front right?

What's the beyond?

It has roughly the same effect.

Try it first with your fingers. Hold up your index fingers pointing straight up in front of the computer screen but in front of your face. Focus on the screen. The fingers should divide into four. Move your fingers until they combine.

If you focus on your fingers you can do the same thing to the screen.

omg I got it!!!

Earlier I was looking out a window and thusly way too far. Now I'm in my bed and its about 3m to the wall and with your instructions it worked great.

It works pretty much the same as you said. Thanks for sticking it out with me!

Np man. Gj.

I'm great at magic eyes / stereograms and have a ton of posters around my house with them, but I still had trouble with seeing the differences in the test images. I easily locked in my focus on the overlapping cat images but only one difference stood out to me. I eventually got them all but it wasn't that easy (maybe with practice I could get there). The differences are noticeable when I focus right on it, but when I'm looking at the whole image it's harder to tell what is missing from one eye.

Are you able to look around while keeping your "unified vision"?

To me, all the differences appeared to be flashing (probably my brain alternates between the pair of images it attempts to "lock in", or something to that effect).

I can get the images to merge but the differences don't stand out.

I find there's a two step process, first overlapping the images (but which makes the images blurry), then letting my eyes refocus so the middle image is crisp. Only then does 3D or shimmer effect happen. Takes some practice to merge the images while maintaining focus for me.

Are you able to confirm the images are completely aligned? You can do this using landmarks, like the brightest stars on the telescope pic. I.e. if you see more than one of any landmark, it is not aligned. You may need to adjust zoom, and distance from face.

I can do magic eyes, but this technique doesn't work for me. My left eye is dominant enough that the whole image just looks like what my left eye is seeing.

I’ve done Magic Eyes a lot, but I’m failing on this. (However, I found the difference in the coffee beans picture reasonably fast without the eye-crossing trick, and before reading what the difference is.)

I challenge you to use this refocusing ability to pass the Stroop Test: https://faculty.washington.edu/chudler/words.html

You are given a list of color names, written in font colors that are incongruous with the written word. E.g. "Red" will be written in a blue font, and "Green" will be written in a yellow font.

You have to say the font color and not the written word.

It's challenging, but it's yet another application where going cross-eyed confers an advantage.

When auto stereograms were all the rage in the late 80's I had a program on my Mac Plus that let me make/edit them and I used to edit for hours WHILE looking at them in 3D. Then one time I was walking down a hallway with a repetitive wallpaper pattern, my eyes did the thing, the entire hallway appeared to shift in front of me, and I stumbled and fell. Still to this day my eyes will sometimes automatically snap into 'alternate' focus when viewing a repetitive pattern.

No need for the Mac Plus program, you can make these in any text editor. Use a fixed-width font and fill a line with a repeating word eg

WORDWORDWORDWORDWORDWORDWORDWORDWORDWORDWORDWORDWORD

Then copy that and paste it a bunch of times to make it multi-line.

Cross your eyes so that the WORD's overlap (all except the leftmost and rightmost). You now see two cursors instead of one. Position your two cursors anywhere you want and then insert a space in order to make the corresponding WORD (or ORDW or RDWO or ORDW) sink into the screen. (Or rise if you parallel-view.)

We used to do this in the computer labs back in 6th grade.

This happens to me easily inside cars with these dotted-breathing roof interior patterns. (Edit: g “perforated vinyl fabric”)

Well, worse than easily - sometimes I cannot get back to normal and am not sure how far it actually is, because the nature of the pattern allows to re-lock at every few cm. I just don’t know where I’m really looking at unless there’s an irregular object nearby.

I don’t share a lot of comments from HN with my spouse, but this made me crack up so much that I just had to. Thanks for the story!

This happens to me too. Particularly when it's on a narrow horizontal repetition (like wooden slats on a wall).

I attribute mine to playing a lot of the game Magic Carpet from the mid to late 90's. It had some interesting graphics modes, including Red/Blue anaglyph 3D and a stereogram 3D mode. It was fun to try to play it, but it used noise for the pattern, so you didn't get textures, only blobby shapes.

On Amiga, there was a 3D demo with this trick. You can "jump in" your eyes to the proper position if you hold your finger at the place where the 3d image should appear, ca. 10 cm close to your eyes, and focus on it. You'll be cross-eyed without knowing it.

Also, I was using the trick as a "cheat" when I played Tiny Lands on Nintendo Switch, it's a "spot the difference" game, but with 3d landscapes (you can rotate and zoom): https://www.dekudeals.com/items/tiny-lands

Note that there is a difference between crossview and parallel view. See this image [0] and try to overlap them. Depending on what you see in the foreground, that is the type of view you're able to see.

Basically, it determines whether the 3D view you're seeing from the stereoscopic pair is convex (pops out of the page) or concave (goes into the page). It is of course possible to learn both views but most people naturally see one or the other. You can go to r/crossview or r/parallelview depending on which one you see.

[0] https://i.redd.it/g5ilwgk99r781.jpg

I find that there are different techniques to seeing both.

If I stare at the image and cross my eyes until focus lock I get crossview where the image goes back into the page.

If I bring the image right up to my eyes and stare through it into the distance, then slowly move the image backwards into my gaze until I get focus lock, then I get parallel view where the image pops out of the page.

I have always wondered the difference between the two and why it happens. Thanks for shedding some light on it :)

EDIT: I have just managed to achieve both without moving my head or the image for the first time in my life! Just by trying to look further 'past' the picture into the distance, and then by slightly crossing my eyes and focussing at a point in front of the picture.

I have been trying to do this for 30 years, and it is only your explanation which helped me to do it. Thanks so much!

I had never done the parallel view before either- spent 5 or so minutes at it and finally got it. For me it's still takes a fair amount of effort to maintain it (unlike cross view that takes effort to stop seeing it instead) but the 3d looks way more impressive somehow. Like the Toronto crowd one- hadn't seen so much depth in a "magic eye" before

I believe it’s better because it is more natural to eyes. You may also want to play with the perspective. E.g. the hall here looks much better from 0.4m than up close on my phone due to the picture’s perspective. https://triaxes.com/docs/3DTheory-en/522ParallelCrosseyedvie...

Cannot figure out what is the difference. I can focus on both seemingly without changing anything, even though they aren't both in focus at the same time. But I don't know what I'm doing differently, I just move my eyes up or down, adjust a bit, and that's it.

Which one is in the foreground vs background?

Note that for parallel viewing the left edges (or centers) of the images should not be farther apart than your own eye spacing aka interpupillary distance (IPD) sometimes just called PD.

That imgur may need to be shrunk depending on your screen for parallel to work.

I can do both pretty comfortably, but there’s a definite bias to parallel, way easier for me.

This whole "just cross your eyes" thing has never worked for me, not once. I've seen these strange patterns printed on the backs of notebooks that supposedly make some sort of 3D effect when you "just cross your eyes". Later, when I saw similar images online, I was able to at least visualize these hidden shapes by opening the image in photoshop, duplicating the layer, setting the copy to "difference" and moving it left or right. The regular texture would eventually disappear and the shape would emerge. It's still a mystery to me what it feels like to view these the intended way though.

Here are some tips;

1. When you cross your eyes, gradually let them return to uncrossed. Try to do it as slow as possible. Along the way, try to line up any structures that you see in the image that are repeated from left/right half.

2. Once you are able to hold a cross-eyed gaze long enough with lined up left/right half, slowly move your eyes between different features near the middle. Your eyes will naturally want to start to focus and match up pieces.

3. Don't be too far or too close to the image; they are usually easily viewed from comfortable distances. If the image is too big, make it smaller. It's usually easier smaller.

4. Initially, when you cross your eyes, or look through the image, it will likely be blurry. This is because your brain naturally associates accomodation and convergence with also changing focus. You'll learn to decouple those things and you will more quickly be able to go from focusing on the 2D image to crossing it without changing focus much.

There's a whole bunch on this site: https://www.magiceye.com/stwkdisp.htm

> 1. When you cross your eyes,

So, how exactly is that supposed to work?

I can manage some de-focusing which makes me see 4 images rather than two. Is that part of it? Otherwise, I don't get it.

I used put my finger halfway to the object, look at my finger until the crossed images in the background converge, then remove my finger and let my eyes stay in the same spot.

Now I can do it without the finger.

> until the crossed images in the background converge

that's the issue! like an OP i never was able to "converge" the images. for me it is phisically impossible: they are too far apart and never come closer. maybe because i have an astigmatism.

That's exactly it. You have to bring the "copy" of the left side to overlap with the "original" right side. Then move forward/backward until the overlapped 2 come into focus. The shimmering should stick out, was so shocking when it finally clicked for me.

Same here, but I always imagined that for it to work, I would need to have roughly equal vision in both eyes, which I don't. Everything is blurry with my left eye, and no glasses or lenses have ever helped. I attribute this as the reason.

Suffering from the same exact plight

I've also always had a hard time with these. I suspect it's because one of my eyes was slightly lazy when I was a child, so my brain learned to put more importance on the signal from the other eye. When I cross my eyes, the image from the better eye tends to just totally override the other one, so it can be really hard to see these kinds of effects.

I have exactly this as well. My optician explained it as my brain would use the information from the lazier eye only if there wasn't any information from the good eye. Just tried the eyes crossed trick on the easy image in the article and the 3rd image in the middle is the right one. If I let them drift apart so there are 4 images I can see the left one and the difference (because I'd already found it), but as soon as I force them to overlap the left signal disappears and I'm only seeing the right image. I've also never managed to do a magic eye or anything, and 3d movies just give me a headache.

I seem to have the same thing. I can't get double images or any tricks at all.

I tried putting folded paper between my eyes to divide the images in such a way that I would only see left side with my left eye, and right side with my right, and I can alternate between image from left and image from right, but I can never see the image at once, or right side when I'm using my left eye.

I just spent 30 minutes trying to get any of these examples to work before it clicked.

What worked for me: I’m not “crossing my eyes.” Trying to cross my eyes precisely enough to get the two images to overlap was impossible.

Instead I’m starting by crossing my eyes until a third out of focus image starts to appear between the other two images, then I immediately abandon trying to cross my eyes and instead focus on bringing that third image into focus like it’s “floating” in the room at a different point in space than the page its on.

Apparently the circuits in my brain and eyes are good at this. As soon as I can get the “third image” to show up by crossing my eyes, I can “look” at it and my eyes snap perfectly into position.

After about 5 minutes of practicing I can focus on the third image in about a second from the time I begin to cross my eyes.

On the third image, the differences between the two images “shimmer” like a holographic foil on a playing card.

Doesn't work for me either. I just made myself queasy while trying to cross my eyes for ten minutes haha

This I think is an underrated tool for scientific visualization. I made a matplotlib add-on that will let you make stereogram plots of data, and use this cross eyed or parallel eyed techniques to see it in 3D. https://github.com/scottshambaugh/mpl_stereo

This is really cool! it allows you to see 2D charts in 3D without actually rendering anything in 3D

Incredible!

I'm frequently surprised by the amount of seemingly ordinary skills I picked up as a bored child that other people didn't. This was an obvious way to solve those "spot the difference" pictures in magazines.

I wonder what skills other people picked up that I didn't.

Some recent example of things I shared:

+ When your belt buckle hangs a little loosely on the front of your pants. You can hook the buckle's prong onto the front button of your pants and it'll stay put. So many people are excited to learn this.

+ Putting a jacket or any open-front garment on quickly. I saw someone struggling to maneuver their second arm in a tight jacket behind their back. I explained that if they hold their jacket out in front of them, put their hands in the arm holds, and slide their arm in further as they swing it around their body they'll get it on in a moment. It's also more stylish. They were so surprised.

My odd claim to fame which is hard to garner praise for is that when I was a kid I always followed a certain pattern when I did something on a left or right foot. I always tried to even it out. So if I pinched my left toes, then I would do my right. But then I would undo that by going right then left. And then I would undo that by undoing the entire thing: right left left right. And the pattern went on:

LRRLRLLRRLLRLRRL…

and so on. It seemed easy enough to remember because you would just undo what you did last.

A few decades later and I learn that’s the Thue Morse word (1) which has many interesting properties like being overlap free. Unfortunately it didn’t give me any kind of advantage when studying combinatorics on words. Just a weird “wait… where have I seen this before?” moment.

[1] https://en.wikipedia.org/wiki/Thue%E2%80%93Morse_sequence

I did the exact same thing, due to a feeling of wanting to "even" things out between right and left. Blew my mind that it was a known pattern; after watching this video: https://www.youtube.com/watch?v=prh72BLNjIk&t=549s

I'm always reminded that we are all more alike than we realise :)

> When your belt buckle hangs a little loosely on the front of your pants. You can hook the buckle's prong onto the front button of your pants and it'll stay put. So many people are excited to learn this.

Yep. And there is a special vertical prong keeper tab on some trousers for exactly this purpose.

For when you feel a sneeze coming on:

- Want to sneeze? Look at a bright light.

- Don't want to sneeze? Scratch your ear.

Ear rumbling: https://www.reddit.com/r/earrumblersassemble/

Eye shaking: https://old.reddit.com/r/Eyeshakers/

Some of us are born with small frenula of the tongue (or we undergo tongue-tie surgery as kids) and can thus perform Khecari mudra without the traditional self-mutilation used by yoga-masters. https://en.wikipedia.org/wiki/Khecar%C4%AB_mudr%C4%81 This can be useful for cleaning tonsil stones or post-nasal drip, but of course you must do so discretely since people would consider that absolutely disgusting

If you want to read out loud for long stretches of time and you hate taking breaks to catch your breath: you can read out loud while inhaling too! (It feels and sounds super weird though so this isn't very useful in practice.)

And here's a party trick related to OP's super power. Pick a distant object and cross your eyes so as to see it double, preferably with the two doubles distant from each other (i.e., cross your eyes significantly). Then, alternately switch between staring at the left double, and the right double. If you do it right, it will look like your eyes are moving in a bizarre alien way.

Here's mine. Look at a patch of grass and ask someone to spot the ant or bug.

It's quite difficult.

But, if you let your eyes go out of focus, the ground will suddenly become alive with movement of all sorts of ants bugs and creepy-crawlies.

This is the first new thing I’ve learned from this thread. I’m going to try it out!

> I'm frequently surprised by the amount of seemingly ordinary skills I picked up as a bored child that other people didn't. This was an obvious way to solve those "spot the difference" pictures in magazines.

Conversely, I'm amazed by the amount of things I discover as an adult are not common experiences or skills for people, despite being considered as such. This includes, for example, having an inner voice (which I do), or ability to visualize things in your head (which I don't).

Wrt. the latter, when I learned as an adult that some people actually can conjure up images in their mind on demand[0], and conversely that aphantasia is a thing, it took me few more years to connect that back to some early experiences in childhood - being bored out of my mind by some well-known novels that my parents and teachers found particularly engaging. Specifically, the ones rich in descriptions of scenery. They'd say that's the best part, what makes the story rich and immersive, and that's what imagination is for and those books are good for exercising it. Meanwhile, I'd feel ashamed and wonder what the fuck are they talking about, while skimming to find where the descriptions end so I can resume reading from there. Well, it turns out what they said was true for them, but is not true for people like me, who can't visualize to save their life.

Well, except in dreams. Which makes the whole thing even more fascinating.

> Some recent example of things I shared:

Interesting. I somehow managed to never learn either, so thanks! Ironically, I realize now I've probably seen people do the jacket swing trick hundreds of times, and yet it never registered in my mind as a distinct technique, much less one that I could learn.

EDIT:

One such skill I didn't pick up until my wife taught me, and that I know many (most?) people don't know, is how to correctly pour liquids out of rectangular containers with off-centre openings. Think a milk box, or 5L jug, or fuel canister. Turns out, you shouldn't flip them to give the liquid the shortest path to destination, but the opposite - have it flow alongside the entire top edge of the container. This gives you steadier flow, and you'll spill less. I still find it counterintuitive, but it works.

--

[0] - Fun fact: that makes "undressing someone with your eyes" a literal ability for them too.

> Specifically, the ones rich in descriptions of scenery. (...) skimming to find where the descriptions end so I can resume reading from there.

I've always been good at conjuring images in my mind, but I also skip the drawn out visual descriptions.

I could never enjoy Lord of the Rings due to Tolkien's love of describing trees (of the wooden and familial kinds)

>> Well, it turns out what they said was true for them, but is not true for people like me, who can't visualize to save their life.

I used to be exactly like this - I could not visualize anything. Which was very perplexing for young me - I was astonishingly good at math (winning some country level math competitions even) but could not get past some arbitrary but somehow low level geometry problems. Then it struck me - I could not see the solutions in my head, only on paper, which drastically limited my search space.

But latley after years od doing other thing (including more artsy stuff like drawing) I discovered that I was wrong - its it possible to learn, its just that some people gets this faster and with little effort. For me it was just a other few thousend hours of doing staff that accidentally expanded my visualization ability and then "miracle" happend.

The same was with my supposed tone deafness - guess what, I only believed my self info being tone deaf (real tone deafness is very bery rare). I just was lazy in this departament (in building my ability to perceive tones).

Good old vdiff: https://catb.org/jargon/html/V/vdiff.html

Visual diff. The operation of finding differences between two files by eyeball search. The term optical diff has also been reported, and is sometimes more specifically used for the act of superimposing two nearly identical printouts on one another and holding them up to a light to spot differences. Though this method is poor for detecting omissions in the ‘rear’ file, it can also be used with printouts of graphics, a claim few if any diff programs can make. See diff.

An interesting variant of the vdiff technique usable by anyone who has sufficient control over the parallax of their eyeballs (e.g. those who can easily view random-dot stereograms), is to hold up two paper printouts and go cross-eyed to superimpose them. This invokes deep, fast, built-in image comparison wetware (the same machinery responsible for depth perception) and differences stand out almost immediately. This technique is good for finding edits in graphical images, or for comparing an image with a compressed version to spot artifacts.

Cool site that I often use with this trick to impress some friends: https://www.spotthedifference.com/practice.asp?m=2&l=4

For anyone who wants to learn this, try this way using your finger as a helper.

Put the images in front of your eyes.

Bring your finger between your face and the image at almost middle of the distance.

Now look at your finger.

Move your finger back and forth and notice the background (where your picture is)

While doing this, notice that at a particular distance, the images in background will perfectly overlap each other.

That's your moment.

Pull out your finger and look at that image.

--

It worked on everyone I have tried to teach. You may always need help of your finger or a tip of a pencil or whatever. But it's lot easier to get those images to merge this way.

My eyes seem to immediately refocus as soon as my finger moves away no matter how many times I try this. Before I move my finger away, everything in my peripheral vision is too blurry to be useful.

I've always been able to merge pictures by focusing into the distance, and I thought that's how everyone did it. So I found confusing all the talk of crossing eyes. I tried your instructions and, within 30 seconds, was able to see the cat image by crossing my eyes.

The cross eyed method seems more amenable to different image sizes. With my regular method, I can't merge images if they're too large (unless I step back).

Does this only work on desktop? I am trying this on mobile and the images never overlap. Wondering if maybe my viewport is too smal

Wait, that's not crossing your eyes, it's uncrossing them. Ordinarily if you look at something nearby, your eyes aim at a common spot. But when viewing a stereogram, you need to convince your eyes to aim at a spot more distant than the subject.

This is easy with practice, however IMHO it helps to be significantly nearsighted. Then you simply take off your glasses, and can look at something nearby with infinity focus, which is naturally associated with uncrossed eyes.

I don't know whether it's possible to train yourself to diverge your gaze, i.e. stereoscopically see images that are separated more than your pupil distance. Certainly I can't do that.

For spot-the-difference, crossing your eyes is more effective and easier to "dial in" than uncrossing them. You're essentially making each eye look at the opposite image. If you try uncrossing, then you need to make sure the images are at the exact correct distance to cause them to overlap with that technique, because you can only uncross your eyes enough to look straight ahead.

Looking uncrossed at the images in the article on my phone, I can easily achieve the effect uninterrupted between fully stretched arms and about half that.

Sure, but that's the limit. I didn't say it was impossible, just that crossing your eyes basically works all the way up to your nose.

Is that true? It seems that our eyes are mechanically capable of looking in divergent directions, what's the reason that we're not able to "uncross" them beyond looking straight ahead? (Edit: Anecdotally I can confirm for myself that I'm not able to do it, so wondering if there's anyone that can.)

From a control system standpoint, if you have one control that rotates both eyes the same number of degrees left or right to determine gaze direction and another to rotate both eyes the same (positive) number of degrees inward to control fixation distance, you can't specify the left eye rotated left of center and the right eye right, even if each eye physically can rotate that way. Not sure if that's how eyes actually work though.

It’s a good thing that properly designed stereograms take this into account and don’t require you to uncross your eyes past that point.

That's because you have to find the distance between your eyes and the stereogram to make it work. Crossing your eyes is easier because your eyes can turn inwards far more than they can turn outwards, so it works at more distances.

See my other comment about cross view vs parallel view, looks like you can do one vs the other and the author can do the opposite.

Wow. Thanks to MarkusWandel I discovered I can focus images while crossing my eyes and finally understood your comment. I've always done the "uncrossing" since I was a kid.

While intuitive, I’m not so sure. I look at the center line and slowly cross my eyes until the 3rd image slides into place and then I get focus lock. At no time do I feel my eyes uncross and go the other way. Hmm!

Both work equally well if you just want to spot differences. Cross-eyed view is somewhat easier to do, since people naturally cross their eyes when looking at something close to their face, but there is no natural reason for one’s eyes to diverge. But cross-eyed view also gives a subjectively smaller image, and is also not the usual way autostereograms are made to be seen.

> but there is no natural reason for one’s eyes to diverge.

When you’ve finished looking at something close to your face and your eyes need to uncross. So you do that eye movement while still holding the image close to your face. Note you are looking “past” where the image is. As long as the image is closer than your infinity focal view you can do this, it doesn’t have to be close to your face necessarily, Magic Eye posters on walls do work.

Front page of HN. Funny to imagine thousands of people sitting in the office crossing their eyes at their computer screen right now.

All it did was hurt my eyes. I'll opt out of playing, superpower be damned.

I think the key is not "going cross-eyed" as much as it is relaxing your focus until the images merge. If you intentionally cross your eyes, it hurts. If you de-focus/relax your eyes until the images merge, it doesn't hurt.

That's more for traditional "magic eye" pattern stereograms where you want to relax your eyes to look off into the middle distance behind the subject instead of intensely focusing on something unnaturally close to your face.

For whatever reason this is what worked for me to replicate what the author was describing.

Relaxing focus for me doesn't cause merging or cross-eyed effects, it causes my vision to go too blurry to do anything lol

i had the same thing where best i could get when i relaxed was a narrow merge, and when i crossed my focus was too close to my face to be helpful, plus strain.

sudden clicked after fully crossing 5 or 6 times and then relaxing and was able to hold the "3rd image" very easily. felt like magic, even hardest difficulty was obvious

For me it just does not work right now. Maybe I have bad eyesight, I wear glasses and am past 40. I believe I was able to do this trick in past though. At the very least on psychedelics (various kinds). This also made me able to relax my eyes more, wheras I normally have too much pressure on them according to optician.

Weird timing. I dunno why this works but I've been using it to see mice.

You see, I noticed that I have a mouse problem in my garage. I figure if I've seen one mouse, there are probably more. So, I stood on some stairs in my garage and crossed my eyes to sort of blur the scene. It allowed me to catch movement more quickly and I was quickly watching multiple mice run around the edges of the area.

That seems like not the same thing though, right? You're not doing a diff on two images, you're just losing resolution so you can direct more attention to movement.

I think it's because our peripheral vision is able to observe movements faster.

Hmm. I noticed in lectures, if I stilled my eyes, most of the field of view would grey out, except for areas of motion (eg a lecturer's head or writing arm) which appeared normal. After motion stopped in an area, it would slowly grey out. When a motion started, its area would snap to normal, making it easy to spot onsets of motion. Eventually my eyes would twitch, and the whole field would refresh.

I first read about this back in the 1980s, in an issue of Science Digest. Couldn't find a link or reference on short notice, but here's something from the American Academy of Ophthalmology that explains the phenomenon, with an experiment to see the blood vessels in your eye:

https://www.aao.org/eye-health/tips-prevention/experiment-se...

Apparently, the brain tends to ignore visual stimuli that don't change over a short period of time, which allows you see "around" the blood vessels passing through the middle of your eye. By closing your eye, and moving a penlight around against your eyelid, you can make the vessels cast a shifting shadow on your retina that makes them visible.

The reason you usually see everything out in front of you is that various actions cause your eye to shift about just a little, just enough to cause the image on your retina to shift about enough for the brain to notice.

I've done this in the past with bugs in the grass. If I stare at a fixed point, I start seeing each individual bug moving through the grass, whereas normally they would be really hard to spot among all the fine details of the ground and grass blades.

I have a true vision-based super power.

my vision is so bad with nearsightedness that when I take corrective lenses off, I can focus on an ipad mini screen within 10" of my face and perceptually it is the same as focusing on a distant movie theater screen. No straining, eyes totally relaxed.

With the lights off, it's better than being in a theater. I tried an ipad pro in the Apple store and it felt like I had my own personal unfairly huge IMAX screen.

Unlike when focusing on a movie screen, your eyes have to turn inward to direct the pupils to converge at the physically near iPad. This can cause muscular eye strain (it does for me).

You can get clever and order a prismatic prescription that bends light out, so your eyes don't have to turn inward. I tried it too, but it gave me nausea.

I have really bad vision too (my prescription is left: -8.00, right: -7.50). Tried this out, and yeah, really works! And realized, you need the best resolution screen possible, because you can see every detail. Not sure how much I'll use this is the future, but good to know it's always an option!

Natures own VR goggles.

An alternative technique called “divergence” [1] (pulling your eyes apart) is significantly less straining on your eyes than crossing them (“convergence” [2]) while being equally as effective spotting differences, even on video. It’s also what your eyes naturally do when you watch stereoscopic 3D with tinted glasses—the stereoscopic images are pulled out (divergence) not pushed in (convergence/cross-eyed). I’ve been doing this since I childhood. If you get good at it, you can watch side-by-side 3D videos in 3D with just your naked eye (e.g. VR)! I believe there’s a reddit covering the more prurient variety of that.

[1] https://en.wikipedia.org/wiki/Vergence#Divergence

[2] https://en.wikipedia.org/wiki/Vergence#Convergence

This is what I do, the only issue is that I don't have nearly as much "range" with divergence as I do with convergence, so I have to make the pictures as small as possible when using it to line up two images (as opposed to autostereograms, which usually have a much smaller divergence offset).

Do you have a training method for divergence?

Similar to the finger moving closer and closer to the upper nose technique, for convergence.

It's a little more abstract since you don't have handy moving-reference-object like your finger, but: Place the picture in front of something deep, like a long hallway. Look off at something in the distance behind the picture, like the end of the hallway. Notice how the edge of the picture is a double image. Focus on gradually resolving the edge of the picture down from double-image to single-image, and then do the reverse by looking down the hallway again and seeing the picture go back into double-vision. Just keep practicing that until you get the feel for controlling your depth perception and then try holding the same depth of the hallway while you turn your gaze to the picture and try the same action with your eyes.

Damn! After reading this I was surprised by the fact that this sounded very familiar.

I actually "practiced" a lot like this because I was always amused to notice how we could basically "see through" objects with this double-image thingy (see experiment below).

So I decided to film myself... and I was actually already doing a divergence! Not convergence!

Thanks a lot for your comment which made me realize that.

Experiment:

1. place your phone (handy size/shape for the experiment) in front of one eye (X), at about 20cm.

2. close the other eye (Y) and look at your phone

3. Open Y and look straight without focusing on the phone. By blinking Y, the double-image should appear/disappear, as if it was unveiling what's behind your phone.

4. By closing X and with Y open, looking at your phone, you should see it displaced from where it was when X was open and Y was closed. The size of this displacement is equal to the size of the double-image transparent part.

I didn't know this had a name or was considered a skill. I've done this since the 90's when those magic eye books became popular.

I even managed "impossible mode" in 2 or 3 seconds.

Who's been doing this since they we're maybe 7 years old :)

Checking in!

I’m frequently baffled by how unaware most people seem to be about the absolute basics of how their eyes work. Like, people don’t even seem to be aware of how their stereo perception is largely made from two images, or any of the implications that has. I actively think about the two images maybe dozens of times per day.

Chill out, that's a bit of hyperbole isn't it? This is just a trick for doing a spot the difference puzzle. It's not exactly a daily task most people are thinking about.

Most people at least understand that stereographic vision has something to do with 3D perception because we've all closed 1 eye before.

It’s a useful way to compare visual things, which comes up in all kinds of contexts other than these puzzles.

I figured everyone because I had a puzzle book that instructed readers to do this.

We've had these stereoscopic books with hidden images and I never saw any. So I've been failing at this since 7 years old – does that count?

Yup I used to do this with tile floors as a child.

If you can easily cross / unfocus your eyes, it also allows you to see 3D images easily. Try:

https://www.reddit.com/r/ParallelView/

https://www.reddit.com/r/CrossView/

I've heard about this before, but I've never actually managed to do it until just now. I needed to sort of "tune the parameters" a lot so that my eyes were crossed but also focused, since I've had a lot of trouble actually getting them in focus when I'm doing it, and the effect isn't as pronounced as I expected it to be

I think you're still not doing it quite right. The effect is really quite obvious and pronounced.

It took me some attempts but I agree, it's very obvious, the 2nd image made it glaringly obvious after I managed it well on the 1st one.

My eyes get very watery after just a few seconds though, curious to hear from others how common this side-effect is.

I've used this to quickly read through a few hundred page documents given to us only as a scanned pdf which was too low quality to run ocr (at the time) on. The sleazy counter party was very upset when I came back with notes on them not adding the changes we asked for on the drafts they sent back within minutes of them sending them back.

I can’t parse your second sentence.

Uncross your eyes! :-)

(They're saying that the person who send the contract was trying to trick them, and that they were upset when the trick was caught.)

a counterparty is the other person you're signing a contract with who sometimes lies to you and says they changed things when they didn't

It was the grammar I had trouble with, not the vocabulary. A comma before “within” would have helped a bit.

Oh wow you can also use this for contract diffing when signing in person!

Every Asshole knows this trick for targeting spacecraft

https://youtu.be/XGdjKvivJA8?si=lRrfl6rHzAsE7nEO

I've got -7.5 myopia/nearsightedness in both eyes, with astigmatism. As a result, my eyes can easily go out of focus to do Magic Eye or this type of thing. The bonus superpower is, if I take my contacts out and get really close up on something, it's like I'm looking through a microscope; if I happen to have glasses on, sometimes I can also catch the light and focus in just the right way to further magnify what I'm seeing already zoomed in. In those instances I see whatever's reflecting through the glasses, so mostly eyelashes and skin/pores, but it's fascinating nonetheless. Can't see a damn thing beyond the tip of my nose without corrective lenses though LOL

Same vision, and I found it hard to do at first- but super cool when the image appeared crystal clear!

You can use this same technique to view glasses-less 3D (stereoscopic) images. It's also fairly easy to create your own. Take two photos but offset the camera lens by approximately eye-width. Open the image editor of your choice and place the images side-by-side. View the composite image cross-eyed and you are now viewing a 3D scene.

Also worth noting there are 2 versions of this kind of cross-eyed focus depending on whether your eyes are focusing on a point in front of or behind the actual image. This determines which side the left and right eye images should go on in the composite. I find it easier to focus on a point in front of the images but IME most examples online are for focusing on a point behind the image.

that's why they mirror one of the images in "find the differences" in puzzle competitions, e.g. USPC https://wpc.puzzles.com/uspc2024/

reminds me of convolution operation.

The stars puzzle helped me find a speck of dirt on my phone screen.

The funny thing about the stars image is this is a common way to find asteroids, comets. It's not limited to just those. Only instead of a bunch of cross eyed astronomers, they overlay and align the images and do subtraction/difference filtering to see what's left. For comets/asteroids, the dot of interest will move between frames. Even just playing back the aligned images as a timelapse can reveal motion.

Also handy for identifying dead pixels!

It blows my mind that every human doesn't know this. I figured it out as a child. The easiest way to prevent this is to have one of the two images be slightly tilted. I can rotate my eyes but it's much harder than crossing them.

As I understand it, Magic Eye stereoscopic images were originally developed by brain scientists studying how we see in 3D (i.e., how the brain processes 2 eye inputs into a 3D image).

There were two competing theories:

1. The brain first does a recognition pass (that's a house, that's a person, etc.) and compares the two eyes to see which objects have moved.

2. The brain compares the two eye inputs first, at the "pixel" level and figures out which pattern of pixels has moved, then afterwards, applies recognition to the resulting 3D image.

Magic Eye would only work if #2 is the correct theory (because in Magic Eye, there is nothing to recognize until AFTER you convert to 3D).

Add some trigonometry, and this superpower has historical military applications:

  https://en.wikipedia.org/wiki/Stereoscopic_rangefinder
  https://www.youtube.com/watch?v=cbXyAzGtIX8

I didn't spend the time reading the comments to see if this has been said already, but crossing your eyes works but learning to diverge your eyes is better in some situations. It's easier to learn to cross because you can just look at your nose, and you can bring together two images that are further away by crossing than by diverging. But diverging is the way we are normally (when looking across the room say instead of at a book in front of us) so it's more comfortable.

Interesting, what kind of situations does it come in handy?

For whatever reason, it was far easier to do this on my phone than on my laptop, even after trying to fiddle with various combinations of zooming in/out and adjusting my distance to the screen. In some cases, it can also be easier to do without glasses (if you customarily wear them) as it makes the defocusing easier.

The effect itself is basically similar to the Magic Eye stereograms (https://en.wikipedia.org/wiki/Magic_Eye) which by themselves are pretty neat; your brain can rapidly detect subtle offsets in random patterns to reconstruct depth cues. In the case of “spot the differences”, the shimmering is due to the irreconcilable disparity between left and right images, which manifests visually as a glaringly obvious “unphysical” apparition - e.g. flickering between the left/right images, or appearing to be out-of-plane with the rest of the picture.

The specific term for the shimmering mechanism is https://en.wikipedia.org/wiki/Binocular_rivalry

Yes that top reddit comment is right. Years ago those magic eye pictures came out and at first I struggled to see the 3d pictures. Eventually it became trivial. Then somewhere I noticed it worked really well for those spot the difference puzzles. They often come on kids menus at some restaurants. I could spot all ten differences in seconds and my kids would be amazed. I finally tried to teach them but they found it hard to do. But ya in reality what this girl did was super easy and not challenging in the slightest. When you do it and cross your eyes inwards you cross your eyes until the pictures line up in the middle. The majority of the picture will be clear but any spots that are different will seem blurry. The trick is just not focus on anything in particular and just cross images until they clear up. Then make note of where it seems blurry. Cool trick but definitely ruined spot the difference puzzles for me.

What's astounding about this is simply the staggering amount of visual processing your brain is capable of doing in parallel.

We know the direction a sound comes from due to milliseconds of difference of the soundwave arriving in one eardrum and then the other...

Exactly, and it is some form of computing power we normally do not have voluntary access to.

To really blow peoples' minds use both hands to tap the differences, keeping the left hand for the left image and the right hand for the right image!

From your POV the images are merged so your hands will look like they're tapping a single image, but from the audience's point of view you look like a savant with multi-attention!

That's amazing! Within 40 seconds I overlapped the two hard mode images and saw 8 shimmering objects set within a clear picture. It took me a little longer (maybe a minute), but the two impossible mode pictures snapped together and I saw a single shimmering star within an otherwise crystal clear photograph!

You can make the impossible picture (the others too) easier by slightly moving your head back and forth while superimposing the images. The difference will move more than the rest of the image.

I cannot do this by crossing my eyes (focusing on a point between you and the image), I have a hard time getting the cross to stay consistent and it never really "locks in" for me. Instead of crossing my eyes, I unfocus them, effectively look through the image. Once I get the repeating part to overlap cleanly, after a second or two, my pupils adjust their focus and the image fades from blurry to clear in a really satisfying way and kind of "locks in" in a way that takes little to no effort to maintain. With a bit of practice, I can even move my eyes around and look at different parts of the two overlayed images without distrupting the effect at all.

I don't know if it's just my brain working differently or if a there is some confusion in the discussion between crossing your eyes and focusing through an item.

I've been doing this since I was a kid as well. When I was younger some restaurants would have video monitors with games on them, and one of them was spot the difference. I essentially maxed out the score and still held the highest score when I came back in town years later. I wonder if its still around...

Well this is interesting. I was able to find the impossible one within 2 seconds without crossing my eyes. The easy one took about 5 seconds, 3 seconds for hard. I've always been hyper-vigilant with patterns (to a fault), so not sure if that's playing into this.

Is that what other folks are experiencing also? I see most comments are trying it with their eyes crossed, but what about without?

EDIT: ok I just watched the video. No eyes crossed. For the balloons one I beat out the girl in the video by 2-3 seconds. For the birds about the same. The skittles one tripped me up, couldn't find it. The other few I found around the same time, the lights at the end I didn't find in time either. It seems I'm quicker when there's not too many colors involved. Still that's spooky.

I use this for quick comparison of minor differences in code / data (e.g. tables, DNA sequences). Variations in indentation are highlighted also, by standing out of the plane.

It's good to hear reports of successful viewing. I've got a 3d / stereogram photo gallery app on the back burner; sounds like a reasonable number of people would be able to view it. There are plenty of guides on how to learn this; some are linked here https://www.reddit.com/r/CrossView/wiki/index/. You-tube used to have support for this; there are still videos tagged yt3d - just regular videos now, not interlaced.

I wonder if this would be a legitimate form of code diff visualization with VR glasses, just show the A and B for each eye

I use this technique to get web layouts pixel-perfect with the mockup, just put both windows next to one another and superimpose them with your eyes. Works great. There are tools that do this by overlaying an image with 50% alpha but it doesn't work as well.

Last year when there was a bunch of fuss about Kate Middleton not having made any public appearances there was a minor flap where people claimed that a photo she'd released was just an edit of an earlier photo.

There was a tweet presenting two photos, one old and one purporting to be new, where she was holding strikingly similar poses. The claim was that the new one was just an edit of the older one. I used this technique and immediately the minor differences stuck out like a sore thumb- her hand was rotated more in one, her hair was laid differently, etc.

By the way... There is a nice old good article about making real time stereograms.

https://developer.nvidia.com/gpugems/gpugems/part-vi-beyond-...

Many decades ago, during my time as a NASA Space Shuttle engineer, a co-worker couldn't locate a rogue unbalanced parenthesis in a complex program listing, in the days when computers, instead of identifying a particular syntax error, would print lame error messages like "Something went wrong." Worse, we wrote programs by punching 80-column cards -- no syntax highlighting, no color monitors.

My co-worker printed two paper listings, one with the error, one without, and asked me to count parentheses as he was doing, over a dozen pages. But because I knew this "superpower" trick, I laid out pairs of pages and crossed my eyes. A few seconds later I found and circled the error.

"Ta-daa!" I said. He never forgave me.

I find it very easy to overlap images, I think because of the eye exercises I had to do as kid.

I don't recall what these exercises were for, but there were two:

1. Stare at this image of two incomplete cats, and merge them together into a single complete cat: https://www.google.com/search?q=eye+muscle+cat+card

2. This strip of cardboard has a number line on it. Put one end half way down your nose, perpendicular to your face. You will see two lines. Merge them at their furthest point, then merge the next nearest point, repeat. (I think this is called the 'Brock String Exercise', but can't find an image similar to the one I recall.)

When I was little I was doing this on carpet patterns because they suddenly become 3D. It was very fun. But I never realized it could be used for this purpose.

There is also one other similar funny ability I have: Vibrating my eyes. I can willingly vibrate my eyes. I don't think it's any useful ability as I just see shaky when I do it but it's fun to do in front of people. It scares some of them. There is actually a community about it in Reddit: https://www.reddit.com/r/Eyeshakers/

This did not work for me. I was able to invoke a middle image, but there was no shimmering. After I found the difference the old-fashioned way, I realized that the middle image showed the distinguishing feature as it is on my non-dominant side.

Nice to see someone discover this! I've always been partial to spot the differences and crossview images - I am able to cross each eye independently of one another, which makes overlapping these sorts of images very easy. For example, I could cross my right eye, while my left stays perfectly still. This causes instant double vision, and relaxing how crossed the eye is lets me line the images up very quickly. It's fun to do in places with a repetitive wall texture, too - seeing something in real life while adding a faux 3D effect on top of it is kind of trippy. Probably my most useless skill, but a fun one regardless.

I am so remarkably one-eye dominant (my left) that the first image just looks like the right cat to me about 98% of the time. Every once in a bit I'll see the flicker, but even then it's faint and hard to notice.

Jokes on you, my eyes don't work together so I can only see out of one at a time!

Jokes on me - because I learned that today that this is not normal. Now I wonder what other people see...

There's dozens of us!

Thanks to this article I have successfully taken a two-hour break from HN and my computer screen, on behalf of the massive headache I acquired at the same time as the aforementioned superpower.

More things you can use this for:

”Are these two things the same size?”

”Are these things that are supposed to be evenly spaced actually evenly spaced?”

”Are all these things straight/at the same angle?”

”Is the wallpaper pattern aligned everywhere?”

”Is that surface using a repeating texture?”

I may originally have stumbled across this trick looking at repetitive patterns. I distinctly recall automobile upholstery (with a regular recurring ventilation pattern). In particular, abberations in the pattern (dirt, missed holes, etc.) stood out.

Similarly, acoustic ceiling tiles, repeating patterns on wallpaper, rugs, or draperies, building faces, etc.

This may be a superpower to some, or a supertorment to those with OCD ;-)

I have strabismus and have always been good at these games. I wonder if it helps me for similar reasons? The examples on his page were pretty easy for me, though the universe one took maybe 45 seconds.

Funny. I also have strabismus and I've never, ever been able to see those hidden picture games or these things even once.

I never developed stereoscopic depth perception, which I assume is related.

Same here, i've always wondered what other people see. An optometrist once said that I see everything as if viewing a tv screen through my eyes, but having no point of reference it looks normal to me. I am pretty bad at parallel parking though, perhaps that's my lack of 'native' depth perception.

The Toyota Bird's Eye View/BMW Surround View/etc makes it much, much easier.

yea same boat. I've always wondered what normal depth perception looks like. On the plus side, it is fun to challenge people to wear an eye patch and play table tennis or some other activity and see how bad they are when they haven't developed monocular depth perception cues.

Instead of crossing your eyes and attempting to focus, what can really help relax your ocular muscles is to do the opposite: look "past" the images into the distance until the images overlap.

I taught myself how to free-view stereo side-by-side images on my phone but after I did so I found that I would get strong stereo impressions involuntarily just looking at certain repeating patterns in normal circumstances like watching TV with side-by-side images or when looking at patterned wallpaper.

My visual system is pretty weird in general so I don’t know how common an experience this is with others. It’s not bothersome at all because I know what it is but it was a little startling the first few times.

This same technique can be used for a 3D effect: https://old.reddit.com/r/CrossView/

Any recommendations for when you can't get the images to quite overlap? I feel like I can get 75% of the way there, but then they start going the other direction. I can do magic eye easily.

Use your browser to zoom out and make the images slightly smaller

this made all the difference in the world.

Wow that's interesting — trying to cross my eyes produces hellish jitter.

I suspect it's because my left eye is slighty lazy.

But I was able to superimpose the right cat picture onto the left one (it's a lot harder for the more complex sky resort picture). It's pretty eerie, the right picture just slides right up the left one (I did need to figure out the right distance for it).

It doesn't help me pick out the differences though, I mostly only see the right picture, and if try to focus my left eye, the right picture slides out. Still, intersting.

I have no idea how that is supposed to work. If I cross my eyes I see 3 images and the middle one is a superposition of the two but I don't see any part standing out.

It's subtle. You need to make sure the center image is very well in focus first. Then, the "shimmer" appears but it's not really a shimmer so much as a (fairly mild) perceived depth/edge "artifact". It seems to glow but i think this is more to do with it looking a bit like glowy edge based artifacts from 3d movies w/ 3d glasses.

Open the image in the Gimp. Duplicate layer adjust opacity then drag it sideways until they line up. Toggle layer visibility.....

Wait, why isn't there a service for this? Or is there?

Set layer mode to "difference" and everything that overlaps exactly fades to black.

On a stereo image sliding the top image is very interesting as areas at different distances fade at different positions.

Here is an example video I made many years ago with the colors inverted as well for visibility: https://youtu.be/k2-ZZz5rwQE?si=UaKcidDRbNZOftbd

I'm amazed that there's so many comments and yet not a single one is pointing out that the coffee bean is missing from the _right_ side of the image. Not the left.

Incredible! This technique is also used for the 3d visualization of protein structures, it was called "cross viewing": https://imgur.com/cross-views-are-commonly-used-to-view-prot...

You cross your eyes to get the two images to line up, hold it there and then try to adjust the focus of your eyes. It's a neat skill to have.

I found the toolbars and stuff around the edge of the image made it difficult for me to lock onto the crossview image in your example; surrounding it with more blank background makes it easier for me: https://imgur.com/a/NizzRgo

The superpower being writing clickbait titles for trivial posts

I remember doing this as a child on our TV that had a picture-in-picture setting. I would set the same channel twice and cross my eyes pretending that it was 3d TV.

How does that work when the two images are different sizes and overlapping? Did your PiP mode have a split screen option? The ones I've seen only allowed moving where the insert was placed (which corner), but it was always a PiP and never a split screen.

Yes, it had a split screen option where the two images were the same size and side by side. Can't recall what kind of TV it was... perhaps a Sony?

Wow! It really works. The missing bean "pops" out at you. The hardest part is getting your brain to focus on the cross-eyed virtual center image.

You can also use this to display 3-D images. You have a stereographic projection of your image (like those kids' view-masters) and then just cross the eyes and look at the middle image. Only since the 2 images are slightly different, you can have the middle image be 3-D. It takes a bit of practice though and causes eye strain (at least for me)

It's not a great way of showing the image, but it'll do in a pinch.

de-clickbaited: to spot minor differences between two images, view them like stereograms

Autostereogramming it doesn't help me lol

If it's perfect, the overlapping regions just merge in color, i.e. the cat's paw becomes off-white. If it's not perfect, I still have to attend to which parts are popping in and out. In both cases I still have to compare the merged view to the left and right hand sides.

Although it is very nice for illustrating each eye's contributions to the merged view. Just not an attention-saver.

I found it almost instantly, which was by dumb luck.

But in the following few moments, seeing two nearly identical photos side by side soon made me think of stereograms, since I'm into them, and have shot a few in my lifetime.

I then used my eyes to overlap the images.

In binocular overlapped view, the difference loudly draws attention to itself, because it flickers between the two eyes.

It's almost as if there were a blinking LED saying "here it is!"

There's a video game of this called QuickSpot. Back in 2008, this was one of my favorite games for the Nintendo DS. It trains the ability to spot little differences quickly. Sadly, outside of winning a barely known video game, it's not a super useful skill.

https://en.wikipedia.org/wiki/QuickSpot

Back when I studied media and communications, around when the first avatar movie created a hype for 3D movies. Me and a couple of friends decided to try and make a 3D movie for class. We made a custom camera rig out of metal brackets and edited the movies cross eyed since we had no actual way of editing in 3D, worked like a charm, altho, it was really hard to get the 3D right.

Doesn't work if you have lazy-eye, unfortunately! I generally just see whatever my stronger eye sees. It might be a good exercise to improve my weaker eye's sight, though.

I've done this on these game machines 30 years ago when I was 10. I'm baffled that there are still people who have to figure this out.

“Impossible mode” was the easiest for me - took a few seconds. Probably due to the aspect ratio and the size of the images on my phone screen.

Dammit!

I can't uncross, now!

https://www.youtube.com/watch?v=qaz2hxZLycY

I have been doing this forever, if you get the high score over a certain threshold you can get a free game (400,000?)

I would usually get accused of memorizing all the pictures.

You will get bored or a headache before you stop getting free games using this technique.

You can get stifled by the older machines with faded CRT screens. The newer LCD (that's how old these games are...) are usually better to play on.

This blog post was nostalgic. Growing up in TamilNadu India, a Tamil weekly magazine called Anandha Vikatan use to have one page of stereogram where an object will be hidden in it. I found it so exciting to do the eye crossing trick to find the image pop up, made me feel great as a kid when my family could not find the image :) fun times

i didn't use the trick, or read what it was until after i tried for myself. it took me about 7 seconds at a conservative overestimate...

then again, i did outperform my entire national cohort at school in almost every subject by a wide margin... an outlier.

the trick however is very clever, but it wont work in more complicated scenarios where attention to detail matters.

EDIT: after doing the first one near the top i tried the rest. with a bit of warm up its very fast. no tricks needed. maybe a relic of playing these games when younger and having a "once in a generation" level of learning power coupled with training it when very young when learning speed is multiplied by a huge scale factor. i had to zoom the last one, but the other two were incredibly fast, close to immediate. sub second.

EDIT2: the warm up was doing the first image once after reading the first few sentences.

EDIT3: this is not a superpower.

This whole time it's been a Magic Eye problem? Geeeeez. This would've won me so many random challenges over the years.

What an unexpected and fun read to find on HN.

Bonus tip: while focused on the overlapping image in the middle, jiggle your screen, and the diff will move around while the rest remains static. This helped me solve the impossible challenge instantly.

I'd love to learn more about the underlying mechanism here. Anyone can point me in the right direction?

Am I weird for almost immediately spotting the missing bean as soon as the image showed up? It certainly would've taken me longer to adjust my eyes for the cross-eyed trick.

Even the impossible one was harder when trying to use the cross-eyed trick than just visually comparing the two by quickly moving my eyes back and forth.

I've always thought that ability to unfocus the eyes might be related to mental focus. If you have difficulty staying on topic, or a diagnosis of ADD/ADHD or whatever {I'm not equate these} AND find it really hard to do magic eye images... Then please take part in my 'totally scientific study'TM.

Upvotes, I agree, I have mental focus issues and can't do magic eye (upvote)

I have mental focus problems, magic eye is easy for me. (downvote)

Downvotes, I disagree (downvote)

{I should have done an actual survey, sorry; felt cute might delete.}

The most mind-bending example of the magic eye effect I've found is people using it in videos.

Of course, the internet being what it is, someone made a version of Bad Apple with it: https://www.youtube.com/watch?v=RLuGJGyCS90

A ton of comments in here saying this is easy/old hat for them.

Well I'll be the one to say this blew my mind. somehow creating the third middle image, being able to relax my eyes and even scan around this composite image actually made me giggle out loud on my laptop, a very rare occurrence. Thank you to the author.

I that not the entire point with those "find the difference" pictures? To teach kids how to do just this ?

I can get the overlap to lock in, but the simmering effect is weak and difficult to pick out. Probably still faster than exhaustive search, but I don't feel like I'm at superpower level. Maybe my brain favors one eye more than the other? I know I have different glasses prescriptions for each eye.

It tried just after waking up, using my phone's screen, and it worked immediately. Not exactly a pleasant thing to do, but it does work as described.

One of the coolest "immediate novelty" things I've read in a while

Sent it to my whole family

The way your mind locks in and focuses on the middle one seems a testament to the brain processing behind vision we take for granted

Almost certainly a lot of the people saying they are ”crossing” their eyes are actually ”uncrossing” their eyes; focusing the eyes straighter than what would normally happen on the surface where the image is laid out.

This is also how the legendary ”Magic Eye” books were supposed to be viewed. Not by crossing the eyes.

This is effectively how Pluto was discovered (not cross-eyed, but with a tool to help): https://airandspace.si.edu/stories/editorial/finding-pluto-b...

Using this trick, I wrote a program for 3d plot visualization in the 80-s. It computed two projections of the plot, as if looked by left and right eye, and printed them side to side on the thermal printer. If you looked hard enough, you can bring the two pictures together and see a 3d picture!

I used to use that trick with some arcade game that was popular in bars in 00s Spain. People were just impressed!

Is the technique to this exactly the same as the technique to view a 3d stereogram image?

I was able to get a 3rd image to be clearly visible in the middle doing this, on the 2nd image I could definitely seem some spots appear that lead me straight to 3 of them but didn't work for me on the other 2 images.

The left-right full-image stereograms... but those are less common than the pattern-based "magic eye" stereograms. Those are the reverse of this - in the linked image and the left-right full-image stereograms, they're done by crossing your eyes to a point closer to your eyes than the original image.

The pattern-based "magic eye" stereograms are done by looking through the image to focus on a point deeper into the screen further from your eyes.

The latter I think are less painful because they use the more natural depth-perception distances of your eyes instead of using what feels like more unnatural positions, but that might be my bias because I'm a bit farsighted. Maybe they're just more common because they're visually inscrutable at first and so you get the "reveal" of the 3D contour from a single large image instead of two already-visible small ones.

I've been using this to do quick source code diffs for years. I started back on the days of printouts.

The first (easy mode) image worked like magic - I crossed eyes, let them rest and the differences shimmered in a very static 3rd/middle image. Couldn't for the life of me rest my eyes on 2nd and 3rd though. [edit - tried to zoom out, worked on 2nd image too]

I spent weeks doing this, looking at stereoscopic (?) images of protein structures, while a grad student in molecular biophysics. I got so that I could see the overlapped images pretty much instantly. But I'm having a hard time getting it now, even on the easy one.

I tried crossing my eyes, but it’s not working for me; I keep seeing things blurry. Maybe I’m doing it wrong. However, I solved the first two puzzles. For the last one, I just guessed randomly. My guess wasn’t exactly correct, but it was close, just a little distance away.

One thing I noticed: because you're tricking your eyes into thinking they're observing at a different distance, your brain doesn't seem to correctly account for head tilt (my theory of the diagnosis). Anyway, I think you're head must be exactly level with the image or you'll get double-vision/blur

It’s way trickier if you have astigmatism

There are some great examples and detailed explanations IMO of this general phenomenon in the book "How the Mind Works" by Stephen Pinker. It essentially discusses how your brain is doing statistical work to build the 3D model from these 2 stereoscopic images.

I recently learned about this from one of my favourite German podcasts: https://freakshow.fm/fs286-zurueck-zur-vision (Starting at 2:50h)

I picked this up during the magic eye craze of the 90s, and I will never not find it hilarious how people get shocked at my ability to find the differences. I always share the skill too, it’s one of those things people find impossible until they get it and it’s easy.

Doesn't work for me. Just like stereograms. I just don't know how to "tell" my eyes to cross. Maybe similar to how I didn't figure out until I was 20-something how finger snipping works. Maybe by the time I'm 50 I can cross my eyes...!

You dont 'tell' your eyes to cross, you just look closer or further away. Try looking at the image at normal distance, whilst imaginging that you are looking into the distance at a beautiful view or at the horizon on an ocean. It is this difference in distance focusing which causes the illusion.

Actually, given enough practice, you can literally just get your eyes to do it. I started doing magic eye puzzles as a kid and loved it, so just eventually learned how to control my eyes in that way. Even today, if I see any repeating pattern, or even anything vaguely similarly shaped, I can’t help but do it

When they snap together it feels soo good…

Well actually, I've been telling my eyes to cross since I was a child. I can't describe it, it's like tensing a muscle in the eyes or something and you can control the angle with the tension.

I can even rotate my eyes! Did you know we have muscles for that? I trained it in the mirror - try tilting your head and look at your eyes REALLY closely: they rotate a bit to cancel out the tilt.

Whenever I try to do this, the most I get is that the two images touch. The cats in the example are holding paws, but they never overlap. I've been trying to make this work since the old magic images from the 90s, but I've never managed it. I wonder if there isn a hardware limitation related to my eye configuration.

To do it with crossed-eye view, try looking at your finger and slowly moving the finger closer to your eyes until you see a third image come into view in between the two on the screen. At some point your brain will/might let you focus on that image.

The never work for me because my eyes don't work well together. Just not team players. I'm almost always looking through just one or the other, annoyingly usually the one that would least be preferable.

This trick had been used in practice to detect fake banknotes and coins, with a device like a two-sided periscope. It allowed a bank worker to put a real coin on one side and the tested sample on the other, so that any differences can be immediately apparent.

Neat. If this isn't working for you, try on mobile. It's easier if the images are small.

You can also just back away from the screen. For the 3rd one I had to back up about 6 feet from my monitor before it clicked into place, once it is in focus you can move closer to see the difference better.

This helped, thanks.

Amazing! Tiny bit of feedback, it might help to add to the article that there's 1 difference to spot in impossible mode (the other two difficulties say there's 3 and 8 diffs respectively, which is useful to know when attempting).

I always feel like I'll permanently see cross eyed if I keep doing that. It doesn't help that I was accidentally hit in the head by my double's partner racket in tennis and spent like a minute or two walking around seeing double. Not fun.

Claims have been made (outside the medical mainstream) that regularly practicing crossing your eyes helps stave off presbyopia. One does get better at seeing stereograms with practice, so it seems like it at least improves some type of muscle control.

Okay, but my eyes hurt now.

uh dunno.

25y ago, i was working behind a 30" tube monitor (a ~35kg hog), with 1 inch thick frontglass.. and one day, one of my eyes started to focus on the (closer)outside of the glass, the other on the (farther)inside of the glass. Could not shake that with closing/blinking. Worse, later, when i got into the car, the closer eye focused on the windshield - instead on the landscape ahead.

Took 1 week of everyday 1-2 hours staring far away at the ocean, to revive. AND removal of the monitor :/

I couldn't do the cross-eyed thing, but it took me maybe 20 seconds to spot the difference just by looking at sections of the images. But I'm not sure that would have worked had the missing bean been buried in the denser part of the photo.

My Piano teacher used to have this book on her coffee table with images like this. You could blur and cross your eyes, and the image would combine to become 3D.

But I never knew this technique could be used to spot the difference between images. Very cool discovery!

This is how I help my family when they're stuck on "spot the difference" steam games. It also takes literally any fun out of them, the actual game has to come from not (just) spotting differences, because that task is trivial.

It's funny, it really works.

Was also able to spot the difference on the coffee beans image: https://i.imgur.com/0TcWvWJ.png

Learned it from Magic Eye books too! But using it for spot-the-difference is way more practical - saves so much time compared to staring at two pictures. Kind of feels like having X-ray vision for finding differences

Very cool. After a minute I was able to focus on the false “third” image of the overlap of each side, but I couldn’t notice any difference. It did appear to be closer to me than the screen though.

I can't seem to do this, it seems impossible for me to cross my eyes. Hmmm.

I appreciate the sentiment but "overlay the images by crossing your eyes" receiving that kind of incredulous reaction is really funny and kind of sad for me. I hope it's just amateur editorializing.

This is called 'vdiff' in the Jargon File: https://jargonfile.johnswitzerland.com/vdiff.html

This is also how I used to do Magic Eye images when I was a kid. Although the stereoscopic image was inverted on the z axis, it was a lot easier than to cross eyes by looking further out into the distance

I've used this method as a diff tool for years. Be it code or product comparison, like CPU specs, or these "spot the difference" images, crossing the eyes can be really useful.

Wow so cool! It really just bounces out. I used to love those Magic Eye books. There's something meditative and calming about that sort of focus. This post was really cool!

Fascinating!

I was able to grab focus for the first image. Found it hard for the second and third image. I focused on the first one and then scrolled down to the second and third - that made it easier for me.

my grandmother used to tell me if i went cross-eyed too much, they'd get stuck like that. it took me until a google search at age 15 to see that was an old wives' tale...

After a short period of training, I got to the point where I can see the third image which I can focus on. However, the differences are very subtile and don't stick out at all :/

Try the second test image (the one labelled "Hard", with the snow). That one was far easier for me than the first (the cat one).

Indeed, that did the trick. Thanks!

Some repeating tile patterns like stripes will cause my eyes to do this automatically and it's really weird and annoying because everything else gets blurry. Fun trick though.

Remember the old magic eye posters? Like the static you'd see on an old untuened TV, in monochrome (but some odd colour like puce, cyan or bile)

"It's a schooner"

Validates a claim in the predictive processing paradigm. The diff between actual and expected is what matters to error correction. That's where all the relevant information is.

Feel like people who are old enough to remember that 6 week period in the 90's where those Magic Eye 3d Stereogram pictures were everywhere have a big advantage here.

I instantly knew as soon as I saw the image. It's the Magic Eye trick. The same one you use to view stereoscopic images. The differences will just flicker.

That's so cool, thanks for sharing this. I managed to do all of them, in the impossible one I identified correctly the area, but couldn't pinpoint the difference.

You can also now free-view stereo image pairs. Congratulations.

I feel old knowing https://en.wikipedia.org/wiki/Magic_Eye

This does not work even in the slightest. When I cross my eyes, the image becomes wayyyy too blurry and its hard to keep it in the center for more than a second

It works for me like every tenth time I cross my eyes to look at a "spot the difference" picture. I don't know how it works for people instantly.

That's how I used to help my grandmother when I was a little child. She always used to remark that the last one (5th) was the most difficult to find.

Funny. I crossed my eyes and found the difference before reading the article.

Somehow expect most people to know this, but I guess that's not the case.

I was hoping to get a new superpower today, but when I was young I was cross eyed. I got this corrected through surgery and can no longer cross my eyes.

i certainly used this trick back in my college days, prompted by a similar technique for "seeing" 3d stereoscopes on a computer monitor. I feel like i learned it somewhere on Eric Weisstein's Mathworld because the 3d objects viwer app let you split the image into two stereo images. Unfortunately java applets have been banished from the internet landscape.

What has happened to me? How am I able to create a combined image and have it be -stable-? This totally works. I’ve been mutated.

It just feels like I'm going to harm something if I leave them crossed more than a split second and I stop.

This trick is interesting to me as someone who mixes records. I (and mixers in general) have a lot of different tricks for making mono audio objects in the mix feel stereo or have a sense of width or depth.

Examples include:

1. Delaying the left or right channel by a few ms (Haas effect).

2. De-tuning one of the channels by a few cents

3. Boosting an EQ band on one channel, with a complimentary cut on the opposite channel.

...and many more.

These are usually very subtle changes that our stereoscopic ears have no problem detecting.

In any case, when we need to do some forensic searching for possible differences between two near-identical channels we'll invert the polarity on one channel and then sum them. The resulting delta sticks out like a sore thumb and highlights even then tiniest differences between the files.

So it's fascinating to discover that we can easily do something similar with our eyes to find the differences.

I'm not sure this works if you have astigmatism

Having similar acuity in both eyes made a huge difference for me. I'm somewhat astigmatic but was able to do this eye "uncrossing" trick just fine. I had a significant loss of acuity in one eye and that's what left me unable to do this (or to watch 3D movies).

I have a small astigmatism (and wear glasses) and I was able to do it, but I feel like if I did any more today I'd have a headache.

I did until it was corrected with LASIK a year ago, and I could still do magic eyes, both with and and without my glasses on.

Stereograms have been used in structural biology publications for many decades now. Google 'stereogram structural biology'

I used to play this game with a friend when we were at the pub, once we start struggling spotting the differences we know we’re drunk

I can produce the third image by crossing my eyes, but one eye dominates and all I see is a cat with three stripes on its head. :(

I’ve tried this in the past without luck, but suddenly I can do it now after reading about the subtle “shimmer” effect. Very cool!

Those kinds of puzzles are part of the CCAT test (annoying test for "cognitive aptitude") and I used this trick.

As a kid I learned to see stereograms in 3D by crossing my eyes. Exact same technique. Comes in handy for Mars images today.

That's fun, it worked for me as well. I could spot the difference in all images, including the 'impossible mode'.

I've never been able to 'lock' the two images together like this with my eyes focus. That was incredible.

Please stop using that RSS icon on your "Subscribe" button if you don't intend to provide an RSS feed.

I knew some people who used it to compare aerial photos (though generally a special device with mirrors was used).

> though generally a special device with mirrors was used

Maybe this: https://en.wikipedia.org/wiki/Blink_comparator

No, a modification of this: https://en.wikipedia.org/wiki/Stereoscope

half-off-topic..

i have ~1 diopter shortsightness. Was less before, slowly going up. So screens are getting blurrier. Have glasses but still try avoid using them.

If i put the (flat edged) TV remote control at about 10cm from my face so it horizontally shadows lower half of both eyes, i see perfectly (without any glasses).

go figure..

Semester 1 when getting a BFA in painting the prof told us to do this to help tighten composition

As someone with a lazy eye it's kind of hilarious to me that this isn't common knowledge.

I can do the 3d images in kids books but cannot make it work for spotting the difference

human stereo vision processing has incredibly sophisticated noise filtering capabilities that are still hard to replicate in software. The shimmering effect people report is essentially your visual cortex highlighting areas where the stereo correspondence fails.

Am I the only one who cant do that? Or does me having aphantasia has anything to do with it?

It would be pretty weird for aphantasia to have something to do with it, it's pretty much using the same technique one can use for cheap 3D effect with 2 videos from cameras slightly apart, it has everything to do with our bifocal abilities and not much else as far as I can tell.

I found two differences in the last picture. Turns out the second was dust on my monitor. XD

I was really good at the random dot stereograms. This is a really cool recasting of that skillset.

I think thats the best part of this skill. Everyone did 'Magic Eye' images as a kid, but to be able to take that useless skill and apply it to something more useful and interesting is really cool.

Wait, this is news? that's how I always solved those puzzles, I thought everyone did that

Dumb question: How do I cross my eyes? can someone explain this method in detail?

Every 80’s kid knows this trick from those old books where you cross your eyes to reveal images.

I was able to do it for the first time after reading this webpage with the technique, cool!

As usual, this doesn't work for me because I don't have stereoscopic vision.

I've been doing this for years and always considered it my secret little hack!

Great read. Not sure it was worth being stuck cross-eyed for the evening, though.

Image worked but when I tried with text it did not work. Is there some trick to it?

related: if you have a side-by-side 3d image/video you can do the crosseye to see it in 3D without any special display/glasses.

it's just that your eyes are gonna be tired after a movie session.

This is exactly the same skill needed to see 3d pictures (aka autostereograms).

Easily defeated by arranging the images vertically.

Or at least, makes it a LITTLE bit harder.

I can overlap. But still need to match overlap with anyone.anyway interesting

I've discovered I can't cross my eyes. Any techniques ?

1. Get a bit closer to the screen so you can see both images clearly.

2. Now, cross your eyes and aim to overlap both images.

3. Draw the rest of the fucking owl.

Seriously. Ever since my physics teacher in high school tried to get the class interested in stereograms, everyone and every article I see talking about it treat "crossing your eyes" as an atomic, trivial step. It isn't. I for one have no first clue how to do it, it's not a distinct operation I know how to perform. Perhaps this is because I am nearsighted and wear glasses.

Still, I wish articles like these focused on explaining how to do the whole cross-eye thing, because once you master that, everything else becomes instantly self-apparent and doesn't need further explanation (I know because I did manage to accidentally cross my eyes once or twice while looking at a stereogram, so I know how the effect looks like).

EDIT: FWIW, I compensate by using another trick for diffing documents with Mark I Eyeball - get them printed on separate pieces of paper, put one on top of the other, and hold in front of you with some bright light behind you (Sun, or your phone's flashlight, will do). Not as good as crossing your eyes, but something I can reliably do.

Corporate needs you to find the differences between theses two images

Learned this at a young age with the Highlights magazines at the dentist.

This is a game mechanic in one of the trials in Ace Attorney Chronicles.

using the same trick, watch this video: https://www.youtube.com/watch?v=zBa-bCxsZDk

You can also use this method to watch 3d movies without vr googles.

This is incredible! Works unbelievably well. Thanks for sharing!

Wow. That’s insane! With the trick I can somehow solve them all!

Who's been doing this since they were maybe 7 years old :)

This makes my eyes hurt.

And it's also not really a usefull life or even primitive skill, just a byproduct of our double eyeballs, which are meant for redundancy and depth measuring.

Pass.

(Although it was cool to do it once and see the third image in the middle.)

Very cool. Even the impossible mode one was relatively easy!

For some reason when attempting this my neck starts cramping

It's a sailboat!

Hah, Kevin Smith caught some flak for that one:

" Someone called out Kevin Smith for this on one of his podcasts. According to Smith, on the day of filming, he asked if the picture really was a sailboat, and the prop master said no. When Smith started questioning this, the prop master said that a) it flashes on the screen too quickly for anyone in the theatre to notice, and b) VHS was too low-resolution for people to freeze-frame it to try it at home. So Smith let it slide.

Smith summed up, "Now, thanks to Blu-Ray, I get people pointing this out to me all the time!" "

https://www.reddit.com/r/MovieDetails/comments/9lf52b/in_the...

Hah, old trick, I read pull requests this way for years

TIL you can learn super powers on the internet

Super cool. It works for me. I love magic eye stuff.

yep it’s just like those magic eye pictures that were big in the 90s, once you learn how to see those instantly you can do this trick also

Wonderful! with your write-up, I was able to “see”.

Woah that is amazing how quickly I was able to apply this.

So cool!

This is the coolest thing I have seen on here!!

all i managed to do was make myself very dizzy

Wife was not impressed. That hit home haha.

This is literally a superpower

A bunch of math is like this too.

I can't believe this has 1587 points (already). Has no one here grown up with those Magic Eye books?

dang it i just did this on a zoom meeting. hopefully no one saw me trying to cross my eyes

Damn, it works exactly that well.

ITT: everyone telling us their stories about how great they are at stereograms. We get it, you're all super special.

Do people not know about this?

This is exactly why I read HN

The "impossible mode" example of a starfield is literally how astronomers have found new bodies (planets, asteroids, comets, supernovae, etc.) since the invention of photography.

Typically this utilised a negative photographic plate (so that bright objects appeared as dark against a light background making their presence easier to detect for our visual system), and the plates were rapidly flipped. The object which moved or suddenly appeared and disappeared was the new element.

This works for nearby moving objects (planets, asteroids, comets) which would track against the stellar background, or distant variable ones (supernovae, variable stars, pulsars) which would appear and disappear (or brighten and fade) over time.

Now of course this is automated and direct sensor readings can be interpreted, but the childs' game was at one time Best Scientific Practice.

Described here, "How are asteroids discovered?" <https://catalina.lpl.arizona.edu/faq/how-are-asteroids-disco...>.

There are archives of these astronomical plates, and there are projects which utilise older observations so recorded to make new discoveries even now (or in the recent past). I'd first learned of this visiting the Lick Observatory on Mt. Hamilton near San Jose some years back. Key was that old plates were used to compare current observations using the same 'scope, an otherwise now-archaic instrument but not without its advantages. As I recall, the astronomer doing the study was the same one who'd made the original plates many decades earlier, and was doing this as his own retirement project. There's a description of similar work (including Lick observations) here:

"Astronomy's Photographic Glass Plates: Demonstrating Value Through Use Cases"

<https://journals.library.ualberta.ca/istl/index.php/istl/art...>

On plate archives:

"Preserving an Astronomical Legacy"

<https://skyandtelescope.org/astronomy-news/preserving-an-ast...>

"APPLAUSE: Archives of Photographic PLates for Astronomical USE"

<https://www.plate-archive.org/applause/info/>

(dylan604 noted this use case earlier: <https://news.ycombinator.com/item?id=42657956>)

A parallel processor is you!

This is just incredible!

Wow! That was amazing!

It's a sailboat

okay, this is so cool. thank you for the new superpower!

Fuck it does work...

I cannot believe this is unknown to so many people that it's news

I cannot believe (well, I can!) that 10,000 by xkcd is unknown to so many people that it's going to be news to them when they look it up.

Not working for me

Wow, I didn’t know I could do that!!

I’m not sure how this new learned trick, can apply to other stuff… but I’m happy I tried it and it did amazed me haha thanks for the share dude!

1 hour from my tests, my eyes still hurt though!!!

Come on, I've been doing this since I was like 4 years old, this can't be news for anyone, Am i right???

Yes, I didn’t think people would be so amazed by it either. Like it’s mind-blowing that this works or has been thought of. But we first did it once as well, some people just discover it late in life I guess (or not at all).

Thanks! now I have a migraine

and now my eyes are stuck this way forever

I came into this rolling my eyes thinking he acquired some ability to learn and be humble or some programming or management topic... the typical bs you see on hacker news.

Boy was I wrong. This is an actual super power.

A new way of doing git diff, leave both versions of the code side by side and cross your eyes.

New business idea: git diff, but it uses Mechanical Turk to hire an army of cross-eyed diff spotters.

There is a wonderful stable diffusion prompt here.

I sure didn't expect there to be a plausibly work-related angle when I came to this thread

It sounds like you mock, but: you can do this, or near enough, and you can do it already, and it works really well!

0. Pick suitable tool. Firefox works. Notepad++ works. GIMP works. Emacs, not so much, but if you use Emacs, you know that you can fix this

1. Load file A into a tab

2. Load file B into a tab

3. Close all other tabs

4. Hold down the tab switch shortcut key and note the result

For images this is actually pretty decent and I've used it a lot. Good for figuring out what the differences actually are when your image-based tests fail, and similarly after making a speculative change. Let your eyes do the difference operation for you. That's what they're there for.

For text: you'd be better served by some other kind of tool. But text is just an image with letters in it, so the same principle applies. It does work!

(I've previously read a blog post, link to which I of course now can't find, about how old-style Photoshop undo was designed with this sort of thing in mind. Instead of working through the operation queue like normal people, it simply switched repeatedly between previous state and current state - the idea being that you'd make a change that you weren't certain of, then press the key repeatedly to see before and after. No need to think. Thinking isn't appropriate here anyway. Just let your eyes look at what they're seeing.)

Somewhat related, but I've been using the Semantic Diff extension in VSCode, works better than standard git diff.

My thoughts exactly. Could be done with a git diff in a VR headset

If you’re already spending the computing effort to create the VR image…

/s

[dead]

tldr: blogger learns how to cross his eyes for fun and "profit".

Would AI not be able to crush this game?

`memcmp` would be able to crush this game, but the fun is in doing it as a human!

15 lines of Python would be able to crush this game. But that's not the point.

Easy, fellas. . .