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.

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

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.

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.

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!

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.

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.

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.

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.

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 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)

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.

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.

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.

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.

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

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

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.

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".

You might be too close to the screen.

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

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

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

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

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.

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.

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

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.

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

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.

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.

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.

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.

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.

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.

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.)

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

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.