Optical Illusion: Black-and-White Photo 'Colored' by Your Brain

After going viral on Twitter and then Facebook, this new optical illusion has finally made its way to our feed. It challenges the human brain by using a black-and-white image as a base. Placing a grid of specific colors over the image triggers a kind of "color transfer" to the background. The creator calls it a "color assimilation grid", and it works with video as well. It will soon be part of stable releases of the GIMP image editor.

The Original Image

The image at the center of the illusion shows a group of girls holding a turtle, while a photographer tries to get a close-up shot. The photo, taken in July 2011 by "Chuwa (Francis)", appears to be in color at first glance. However, the secret lies in the grid overlay. Depending on your screen, the illusion may be more or less convincing, but once you load the image into an editor, the trick is exposed.

How the Grid Works

There is a colored grid over the image. When your eyes and brain process the combined content, they tend to "average" or "transfer" the colors onto the elements in the background, from skin to shirts. If this reminds you of the illusion with the balls that are all the same color, it's because these visual tricks often belong to the same family. So, where does this illusion come from?

The Creator and the Video

To answer that, we need to check the Patreon profile of Øyvind Kolås, a digital artist and one of the lead developers of GIMP. Kolås presents the illusion as a "color assimilation grid", and the best part is that it isn't limited to static images. He took a short scene from the Blender-made film "Spring" and published it on YouTube with the grid included.

Coming to GIMP

Furthermore, Kolås confirmed that the assimilation grid will be a feature in the next GIMP 2.10 release and the 3.0 development snapshot. If you compile GIMP from source, you can get it immediately. Kolås also experimented with dots, single-direction diagonals, and horizontal lines, but the grid is the pattern that best sustains the illusion.

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