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Comment by mountain_peak | Hacker News Reader

When my kids were younger, they used to subscribe to a children's magazine that featured a monthly "spot the difference" puzzle. They were amazed when I used to glance at the image and rattle off the one obscure difference they missed.

My trick was based on "magic eye" images I used to enjoy. When I saw the side-by-side drawings used by the puzzle, I wondered what would happen if I "fuzzed" my eyes as if I was looking at a magic eye photo. To my surprise, all of the items that were different between the two images "vibrated" or "shimmered", while the rest of image stayed steady. I repeatedly fuzzed and focused to spot all the differences in a matter of seconds.

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Yep, I do this too. One thing that's cool is viewing stereograms that have differing colors. Some people apparently can see new colors via this method that is not simply a mix of the two colors.

If this made anyone else curious, I found https://m.youtube.com/watch?v=cQCsDfEqr9o from a post with a ‘blellow’ stereogram https://www.reddit.com/r/MagicEye/s/pd2FtY5PnY

There’s some skeptical commentary in the thread as wel.

If I look at that dead center then I get a gradient between the two colors. If I look left or right I get predominantly that color.

Sometimes an inverse gradient will appear and/or it'll shimmer, but I wouldn't say that it's at any time a "new" color.

In in astronomy, they used to use a similar technique to 'spot the difference' between photographs of the night sky to find moving objects. They used a special stereo microscope that would place one image in front of each eye. The images were of the same part of the night sky, but separated by time. I saw one recently at the Palomar Observatory. Here is a more elaborate one from the National Air and Space museum: https://airandspace.si.edu/collection-objects/microscope-ast...

I use this for diffing on a PC, such as when you have a hex editor open that doesn't have a built in diffing feature.

I find a good technique is to load hex dumps in vimdiff.

I even use this technique to find difference of two strings like encoded text, one printed above the other.

Highlights for Children?

Indeed! Great magazine...

I also recall playing a black-and-white space game (top-down scroller) for the original Macintosh where the instructions asked you to tape a piece of cardboard to the middle of the display such that each eye had a separate image of the split screen, which ended up providing a 3D effect without special glasses. I can't seem to recall what the game was, but I could play without the cardboard using the same vision technique (the 3D effect was very pronounced when playing in a dark room).

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