Optical illusion: Seeing color in a black-and-white image

Originally published at: https://boingboing.net/2020/08/27/optical-illusion-seeing-color.html


One of my favorite visual effects is the McCollough Effect. I should preface this by saying that the effects can be long-lived (days or months), so read up on it before you try it.

If you train your eyes on images with horizontal and vertical black lines split by contrasting colors (say red vertical lines and green horizontal lines), then for some amount of time afterward, series of black and white lines will look like they have a bit of a neon glow around them, in the color opposite what you trained them with.

Unlike the video’s effect, you don’t have to stare at just one place in order to get the effect. You can let your eyes wander, so long as the training images fill as much of your field of vision as you’re trying to affect, and you can (and should) go back and forth between the two training images. The longer you train, the longer the effect persists - I once made training images that filled my whole monitor and spent a half-hour lunch looking at them. I could see a faint glow on high-contrast vertical and horizontal lines for 2-3 days afterward. I could see hints of it in the special testing image for much longer.

From what I read years ago, it was suspected that this effect is from part of the way the brain normalizes your vision, like the effects in the video with color standardization. The vision center of the brain apparently knows that there is not supposed to be a correlation between edges and colors. By training in such an environment, the brain thinks something is off and tries to correct for it. When the training stimulus is removed, this compensation causes the opposite color to be seen.

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I love optical illusions. When the whole dress thing happened, I was jazzed because a bunch of people, after they were done arguing which was right, had the opportunity to learn a little about our visual system and how it interprets color. I’m sure not as many people took that opportunity as I would have hoped, but still.

Also, examples like this, that show how easily our eyes (and by extension, our brains) can be fooled, should instantly discredit anyone who ascribes to the sophistic “trust your own eyes” philosophy that led to stuff like flat-earthers.


If you don’t already know the artist I would strongly suggest checking out the work of James Turrell. Images of his work don’t work in books etc. but having seen them in situ they are profound.

A similar thing happens when the brain interprets audio input. How can you hear the root note of a timpani or double base through tiny air motions from headphones - low frequency waves on a bass are the length of a small room? The brain interprets the harmonic content in the upper ranges that the small speakers can reproduce and interpolates the fundamental note.

Audio visual perception is an amazing study.

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There is a Turrell installation hidden in Las Vegas that I’ve tried to see a couple of times, but couldn’t get the timing to work out. His work is definitely on my list of things to experience!

And yes, sound is so subjective. Audio perception is fascinating

One of my favorite is a black and white spinning disk, which tricks the mind into seeing colors where there are none. Not sure how the link video will show due to scan rates, but in real life the mind is convinced there are colors.


This is what I thought the post was going to be about from the short title.

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