As a child I became convinced that everyone was taking the piss out of me. Aged nearly forty, I stand by that!
I still can't see the damn things ;-)
Once you can do that it's as easy as moving your eyes down while maintaining your eye position (and if that really doesn't work you can try drawing two dark black lines down the image.)
Enjoy! Unless you can't get those dots to overlay in which case you at least then know why you were never able to do it :)
Basically, what I do is, imagine you are looking through the image and past it, like if you were looking through a tiled window and wanted to focus on the on something outside small. Then after refocusing your eyes (you can't blink or else it'll reset your eyes) keep doing it, it can take you ages, what you'll see are the tiles.
Also what helped me, is focusing on a single point and moving back and forth.
Do it again with two fingers in front of you, you should be able to see four fingers. Adapt how much you squint in order to see "three" fingers (i.e. two of them overlap). (Practice to perfectly control how much you squint: you should start at zero squinting and increase slightly until you achieve the overlapping.)
Once you can do that easily, replace your fingers by the SIRDS generated on that website. Instead of two fingers, you use two features on that image that you see are repeating. You choose two of them that are next to each other. You do exactly as with your finger: turn those two features in "three". Now I think this is the harder part: as you do that, you have to relax and let your view adapat so as the image becomes perfectly neat (not blurry at all).
EDIT: As a cue from another response, focusing on your own reflection works really well (even if the reflection is not super visible it works for me, although a smidge harder).
It might help to practice explicitly changing your focus from far to close and back to far (the back to far part is what you should pay attention to and practice). Do this practice with your monitor's edge (or the text at the very top of the monitor) and the paper. Get used to how the monitor looks when you're focused well behind it (your brain/eyes "naturally" want to shift to a close focus... this is likely a survivability trait... things close to your head are important/possibly dangerous... so overriding this takes careful practice/effort/concentration).
Try positioning the image at the top of your monitor (if you have a narrow bezel) and make sure the image is only about two thirds or one half visible (i.e. scrolled up a bit). Behind your monitor, a foot or two away, have something easy to look at (eg. blank piece of white paper). Pay attention to your peripheral vision... but don't change where you're looking... just be aware of what's in your peripheral vision, especially the weird color pattern. It should appear "weird" because it doesn't match your memory of the actual pattern... if you know what I mean. Still focusing on the paper, and paying attention to your peripheral vision, move your head up/down a little bit, try not to move your eyes... i.e. where you're focused should move up/down the same amount. You should notice the weirdness (in your peripheral vision) of the image increase/change. Now... if the paper is far enough behind your monitor... when you move your head down farther you should start to see "something". By focusing farther away the "something" should become much clearer. Gradual move your attention to the "something" (keep moving your head) and your focus should naturally move out and the items become clear (especially if you're moving your head... the background will move behind the items in the foreground).
Note for the image from the article the items are just a few narrow triangles, some close, some farther away, some overlapped.
Also... make sure your eyes are level with the image. Rotate your head a few degrees (10... maybe 15 or 20) and the image cannot be seen.
The first time you see one of these images you might be disappointed. They are just 3d shapes wrapped in a strange color pattern (the same pattern in the background and on all objects).
Is it a wave? A recursive wave? wtf, X
I'd suggest limiting vertical panels to 7 or so, which would make it easier to see in 3D on a small screen. That goes for any SIS, whether random or bitmap slice "surface". To my sensibilities, the random dot type, as opposed to a normal bitmap image slice used as the vertical panel, is much less visually interesting and gives the viewing eyes much less to grab onto.
IMO a carefully chosen bitmap thematically or visually coordinated with an elegant carefully drawn depth map creates a work of art that can be appreciated for its interesting shape and color even by viewers who can't grok the 3D effect.
Besides, looking at something beautiful can motivate people to keep trying to see the 3D part come into focus, and eventually some do succeed. When that happens it really is like "magic".
I've never been able to see one of these things on a screen until now. Now that I have, I really want too see an animated one.
The coolest thing so far is that you can click "redraw" and you'll cut to the next one and your eyes will already be focused for it.
There's pretty recent music video that's all autostereogram: https://www.youtube.com/watch?v=2AKtp3XHn38 The dots at the beginning are helpful.
I don't think MagicEye.js is fast enough to do a bunch of frames on the fly for some real-time animation, unfort. But if you already have the frames rendered you could stitch them together into a gif.
h key toggles the height map.
It uses a simplified version of the MagicEye.js algorithm which generates horizontally repeating patterns for hard height changes in the source image. That's why I went with a plasma in the end.
Source is available here: https://github.com/philippstucki/sird-plasma/blob/master/3dp...
To properly view them, you need to go wall-eyed, by focusing on something behind the screen. This is something that I have not been able to do yet.
It's a good technique if the repeating strips are really wide. On my screen at least, the strips here are pretty narrow, so it should be relatively easy to converge your eyes correctly.
Having said that, I don't know if this script is resolution independent, so it's possible that on some monitors the strips are a lot wider than they should be and that could be giving people more trouble.
Position yourself with something behind you (such as a window) that you can see reflected on the screen. Focus on the reflection so you are looking "through" the screen. Now re-focus on the screen, but not immediately! Hold your focus and let it "slip" as slowly as possible. At some point your eyes will converge at the right depth and you'll catch a glimpse of the shapes behind the screen. When you see the pattern starting to come into focus, lock your eyes onto it. The first few times you'll probably catch a glimpse but fail to lock on. Repeat until you get the hang of it.
Once you can see this, alternate between looking at your fingers and looking at the distance. Once you've got the mechanic down, you can start intentionally unfocusing without anything in the distance to look at, which is what it takes to see a magic eye.
I messed around with SIRDS quite a lot in the 90s. I found it hard to see them at first, but the reflection technique initially worked for me and after a while, I had no problem seeing them and even started seeing them by accident in wallpaper patterns and the like.
Another thing that makes a difference is the width of the strips used in the stereogram compared to your IPD. Depending on the width of these, it might be easier to sit closer to, or further away from the screen. Once you get the basic technique you can tolerate a wider range of widths, but at first it can be tricky. It might help to start really close to the screen and slowly move your head backwards as you try to focus.
edit: like myself.