The world isn't black and white, but this photograph is. That looks like a color photo, but what are you gonna believe — us or your lying eyes? To be clear, there is a modicum of color, but as Digital Spy described, it isn't coming from the photo itself, but rather a series of colored parallel lines overlaying the picture. Posted to Twitter in 2019 by artist Øyvind Kolås, this image demonstrates the von Bezold spreading effect, commonly referred to as color assimilation.
This illusion isn't new. Colour: How to Use Colour in Art and Design explains that in the 19th century, rug designer Wilhelm von Bezold realized "he could alter the entire appearance of his rug designs by simply changing a single color." Specifically, when he applied an even distribution of "black or white or a pure hue (at full intensity)," the rug's other colors would appear more similar to the new hue. Similarly, the black and white photo appears to have the colors of the lines placed over it.
Per the Journal of Vision, this is the opposite of what happens in simultaneous contrast, which causes colors to appear less similar to their surroundings. Research suggests that having "uniform" surroundings promotes contrast while stripes elicit assimilation. Moreover, stripe thickness makes a difference, with wider lines causing contrasts.
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