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Wow, this is great!

I want to put some of them in my UIs.

These are all super dark, for some reason.
This is cool, but more as a demonstration of interesting CSS techniques than optical illusions in my opinion.

Also, interestingly, I seem to be able to force myself to "see through" all of these illusions except for induced gradients, which I can't stop seeing unless I cover part of the screen.

33 - color fan: There is another interesting optical illusion here: The fan seems to rotate faster when not directly looking at it.
These "dots appearing only while (not) focused" are known as "extinction illusions", namely

    "25 - Appearing Dots"
is "McAnany's type" [1], and

    "26 - Disappearing Dots"
is known as "Ninio's type" [2], according Akiyoshi Kitaoka's materials. (I have recreated them too few years ago [3][4], before getting to the source.)

[1] https://www.psy.ritsumei.ac.jp/akitaoka/kieru3e.html#:~:text...

[2] https://www.psy.ritsumei.ac.jp/akitaoka/kieru3e.html#:~:text...

[3] https://codepen.io/myf/full/XjdmJy ( scintillation warning)

[4] https://codepen.io/myf/full/jMqoMW ( scintillation warning)

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Heh, I used to do these in Excel.
They could make capchas out of these.
"Please select the dancers spinning to the right"
What would be most interesting is using optical illusions to help decode how brain visual processing is done.
This coca cola illusion is my favourite one https://gagadget.com/en/446542-a-photo-of-a-coca-cola-can-th...

Coca cola appears red when no red at all is used in whole image

This is a great illusion, though I often see that people try to explain this (and a similar image of strawberries) as "our brain knows this object is supposed to be red so it fills in red", which is not what's happening - it's based on color contrast like many other optical illusions
The background on the can is a very light red. I know from painting murals that a light color close up looks darker from some distance.
I thought this was going to go the other way.

Worked on a project that wanted to make everything a different grayscale color. It was out of control already when someone one day complained that two pieces of text were a different color.

They weren’t. They were identical. But they were on two different background colors which make the optical illusion that they weren’t. And I reminded them for the twentieth time that we were using too goddamned much gray.

On #4 (White's Illusion) it looks like for me that the gray bar that is surrounded by black is brighter than the one surrounded by white instead of darker :#