An image of strawberries that creates an optical illusion has gone viral.
On Feb. 27, Japanese psychologist Akiyoshi Kitaoka uploaded an image of a plate of strawberries to his Twitter page. The image appears to be tinted blue.
As Kitaoka wrote in the caption, the "strawberries appear to be reddish, though the pixels are not."
It turns out that the photo -- and our misinterpretation of it -- an example of a neurological phenomenon known as color constancy.
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Color constancy is the process by which our brains automatically correct the color of objects that have been altered by different lighting conditions.
Bevil Conway of the National Eye Institute explained to Vice how it works.
"If you imagine walking around outside under a blue sky, that blueness is, in some sense, color-contaminating everything you see," she said. "If you take a red apple outside under a blue sky, there are more blue wavelengths entering your eye. If you take the apple inside under a fluorescent or incandescent light without that same bias, the pigments in the apple are exactly the same but because the spectral content of the light source is different, the spectrum entering your eye that's reflected off the object is different."
With respect to the strawberries in Kitaoka's picture, Conway said the blue filter itself is an illusion.
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"In this picture, someone has very cleverly manipulated the image so that the objects you're looking at are reflecting what would otherwise be achromatic or grayscale, but the light source that your brain interprets to be on the scene has got this blueish component," she explained.
"You brain says, 'The light source that I'm viewing these strawberries under has some blue component to it, so I'm going to subtract that automatically from every pixel.' And when you take grey pixels and subtract out this blue bias, you end up with red."
As Twitter user Carson Mell demonstrated, the "red" of the strawberries is a grayish-green color when presented against a plain white background. There's no red at all.
The episode is similar to one from 2015, when a woman posted an image of a dress to Tumblr and asked her followers what color it was. The photo quickly went viral, with some people saying it was gold and white while others swore that it was blue and black.
The dress's manufacturer eventually confirmed that it was blue and black, adding that it had decided to restock it due to all the attention it was receiving.
CNN's senior medical correspondent Elizabeth Cohen explained the science behind the controversy.
"It has to do with the tiny cones in the back of our eyeballs that perceive colors in a slightly different way depending upon our genes," she said. "The cones in our retinas -- the fine layer of nerve tissue that lines the back of our eyes -- detect the blue, green, and red in an image. The cones and your brain mix those colors to make other colors."