If you have a Facebook account, or any kind of exposure to social media at all, or a television, you probably saw a lot of this dumb dress last week, as people lost their minds trying to deal with the question of whether it was white and gold or blue and black.
Spoiler, it was actually blue and black, although that didn’t stop people from perceiving it as either or even as switching back and forth between both. You probably even saw a “scientific” explanation of why some people see it one way and some see it the other, although it was probably wrong.
Here’s a real explanation from James Pomerantz, a professor of psychology at Rice University and an expert on visual perception. First, look at this picture, though.
Those squares marked A and B, focus on those. That’ll be important later.
“A couple of things are going on (with the dress), and not all of them involve how our eyes and brains see color,” Pomerantz said. “As people who have studied visual perception or photography or painting know, there is a problem that eyes and cameras struggle with called “white balance.” If you look at your camera closely, there may even be a white-balance control on it that makes this setting for you.”
As an example, Pomerantz says that if you take separate photos of a “white room illuminated with red light bulbs and one of a red room illuminated with white light bulbs” the photos would be reflecting the same kind of light and should look the same. But in practice, say if you stood in both of the rooms, you could most likely tell the difference because you could pick up clues from the environment as to what color of light was illuminating the room.
That brings us back to our picture.
“As hard as it may be to believe, the checkerboard square (actually a parallelogram at this angle) marked A is identical in brightness to the one marked B, even though B looks far lighter,” Pomerantz said. “The reason we see them as different is that we factor in the obvious shadow being cast by the cylinder, blocking the source of light pouring in from the upper right. Because B is in shadow, we must mentally (albeit unconsciously) correct for it being in the shadow. A camera doesn’t know about any shadow or any cylinder or any light streaming in from the upper right. All the camera knows is the brightness at each point (pixel) in the image, and so the camera sees A and B as identical.
“The checkerboard illusion involves just black and white, but the idea extends to the color of the dress,” he said. “The main point is that we can’t tell the difference between white and blue, or between black and gold, unless we have some independent information about the wavelengths of light illuminating the dress.”
The reason people see the dress as different colors, then, is that the photo doesn’t provide enough information to gauge the source of the illumination. So our minds make guesses on potentially faulty clues, like the shadows cast on it.
The dress picture is, if judged by an objective scientific instrument, blue and black.
“If you put a color meter up to the ‘white’ portion of the dress, you’ll see in the red, green and blue readings that there’s a bit more blue than red or green; in that sense the dress is blue. But it could have been white under blue illumination.”
But that’s not the case here. Instead the picture is right and it’s our brains that are unreliable.
“What’s correct is that the dress itself, which is for sale online, is actually blue,” he said. “That means that the lighting under which the photograph was taken must have been a fairly good white — that is, an even mixture of all wavelengths or colors — and thus a flat spectrum.”
[Source: Rice University]