Not the dress again — illusion from two identical images confuses the internet

By Posted on February 8, 2018 12:50 pm

Two roads diverged — and confused the internet (again). In a sequel to that blue-and-black-or-white-and-gold-dress and those green strawberries, another optical illusion is confusing the internet, and this time, not on color. This week, a Redditor shared a photo of what appears to be a road taken from two different perspectives. Big deal, right? Except the images are actually one and the same.

The post shows two images of a street side-by-side. The one on the right, however, appears to slant more towards the right. That’s problematic, because if you overlay the images with each other, it’s easy to see that both images are identical, pixel for pixel.

So why do the two roads look like they could be the opening of a Robert Frost poem? The answer probably has something to do with how our brains interpret lines in a two-dimensional image.

If you take just the photo by itself, the image depicts a concept that photographers call converging lines. If you stand in the middle of a straight, flat road and take a picture, the lines that make up the edge of the road in the distance will eventually appear to merge together. Our brains, however, know that those lines don’t actually touch, but that distance simply makes them appear to grow closer together. Instead of seeing converging lines, the brain sees depth. In the street image, we know that the van isn’t larger than the truck, we know that it’s just closer because those lines allow the brain to see the depth in the image.

That’s why converging lines are popular in photography, because that effect gives a two-dimensional image the appearance of depth. Converging lines give our brains clues of depth in the original scene, since the image is actually flat.

If the brain knows that converging lines don’t actually converge, then why do those identical photos look different? The answer is in the placement of the photos. View the same images one on top of the other instead of side-by-side, and they look like the same image. When the images are placed next to each other, however, the brain uses those same converging line clues to measure depth and assumes that the road on the right is actually forking off of the first road.

As another Reddit user points out, if you cover up the bottom half of the image, the top halves look identical. Move your hand to view the images in their entirety again, and those converging lines tell the brain that those roads are heading in different directions. Mind = Boggled.

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