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.
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. ;-)
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.
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.
Workaccount2 ·6 days ago
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.
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iforgotpassword ·6 days ago
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nayuki ·6 days ago
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.
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the__alchemist ·6 days ago
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.
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robotguy ·6 days ago
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