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

Would AI not be able to crush this game?

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...

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.

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"

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.

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 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.

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.

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.

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 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.

I'm not sure this works if you have astigmatism

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.

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.

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!

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

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

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

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.

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.

Corporate needs you to find the differences between theses two images

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

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 :)

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

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.)

For some reason when attempting this my neck starts cramping

It's a sailboat!

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

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”.

TIL you can learn super powers on the internet

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.

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).

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.

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.

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

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

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

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

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

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

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

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

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!

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

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

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

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.

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

Easily defeated by arranging the images vertically.

Or at least, makes it a LITTLE bit harder.

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.

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

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

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.

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?

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.

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.

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

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

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 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.

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...

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

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!

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.

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]

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 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.

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 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...!

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

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

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.

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

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.

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 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.

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

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.

It's funny, it really works.

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

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.

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.

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.

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!

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 :/

A bunch of math is like this too.

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

This is literally a superpower

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.

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

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!

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

It's a sailboat

Fuck it does work...

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

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!

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

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.

When they snap together it feels soo good…

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/

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

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.

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.

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.

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!

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

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...

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.

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.

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.)

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.

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/

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.

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

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.

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.

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 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.

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.

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.

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 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.

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

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

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.

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?

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.

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.

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.

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.

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.

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.

Dammit!

I can't uncross, now!

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

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

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.

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.

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.

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.

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.

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.)

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

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

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.

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...

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

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

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.

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

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.

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".

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.

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.

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.

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.

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

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)

Is that the crossy-eye porn?

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.

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.

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.

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.

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.

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.

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.

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...

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.

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)

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

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.

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

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.

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

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.

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.

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.

That's the focus in front right?

What's the beyond?

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.

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

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

Np man. Gj.

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

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.

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.

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.

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?

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.

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

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."

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."

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

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.

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.

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.