27 February 2015 will forever be known as the day of #TheDress. Specifically, this one:
That’s a photo taken at a wedding, and Caitlin McNeill and her friends realised that they couldn’t agree on what colour it was. Which freaked them out. And then the rest of the internet.
So what’s going on? A million blogs are giving you answers. Here are mine.
First, we have to understand the incredible job that the brain has to do to figure out what the colours are of objects around us. Light varies in wavelengths, and we all know from rainbows that those wavelengths appear as different colours. A red car is red because its surface reflects lots of long wavelengths (that appear red) and absorbs all the other ones. Except, that’s not exactly true.
The trouble is that the amount of “redness” reflecting off the car will vary tremendously as the amount and type of light changes. So as the sun moves from dawn to midday to dusk (to incandescent bulb) the wavelengths reflected from objects would change drastically. So everything would change colour all the time.
But it doesn’t. Most of the time, things seem to have the same colour. This not because the light is constant; instead, it’s because your brain is really good at figuring out what the original colour was. So how does it do it?
The basic answer is that your brain is not just looking at how much redness is coming from the car; it is also looking at how much redness is coming from everything else in the scene. The “red” thing doesn’t have to have lots of red light coming from it; it just needs to have more red light than anything else in the display. So to change the colour an object appears to have, you don’t need to change anything about the object, you just need to change the context.
If that didn’t make any sense, look at this from Beau Lotto:
You can find the interactive demonstration here. The middle squares of the top and front surfaces look different (brown and orange respectively). But in fact they are identical, as you can see in the demo when you mask everything else. They look different in the main image because of the very different surrounding colours.
So what does this have to do with the dress? Well, it is not at all surprising that the dress appears to have different colours under different circumstances, since colour is so based upon context and the context could change.
But what is more interesting is that two people can look at the same image and disagree. Normally our perceptual systems will agree. But not always. Here is a classic perceptual ambiguity:
The Necker Cube (this one downloaded from Wikipedia) looks like a cube sitting on the ground. But wait… maybe it is floating in midair and we’re looking from underneath? In fact, there are two possible interpretations, and you can see both, but you can only see one at a time.
That seems to be occurring with The Dress. My guess is that different people are perceptually organizing the photograph in different ways, and once you see it one way it is hard to reorganize it and see the other colours. At this stage I don’t think we have a great explanation for why some people see one and other people see the other… but let me know what you think! I’ll update the post as smart people come up with answers!
UPDATE: My friend Derek Arnold pointed out on ABC radio that the ambiguity comes from whether your brain thinks the colour of the dress comes from the light or the dress itself. That is, if you see it as gold and white, you think the gold colour comes from the dress. But if you see it as blue and black, you think any gold in the picture is coming from the light (and therefore is not part of the dress).