The Dress explained

How a picture of a dress can highlight the fragility of our perception of the world

  • The dress colours on different backgrounds. Credit: xkcd

This morning, just like everyone else in the known universe, we at the Ri were bewitched by The Dress, as you can see: 

  • people discussing

    The Ri office in heated debate

    Credit: Olympia Brown

We just about managed to avoid coming to blows.

If you're one of the lucky few not to have already seen it, the picture shows a dress which some people swear blind is black and blue and others white and gold. Once the dust had settled, we thought we should probably try to get the bottom of what was going on, being the home of science communication and all.

So what is going on? How can people have such a profoundly different experience of the same thing? And why, for some people, does the dress suddenly change colour, and then stubbornly refuse to change back? Is everyone going crazy? 

The first thing to understand is that vision is more complicated than you might think and is about much more than what you’re eyes are doing. A huge amount of processing goes on in the visual cortex – the part of the brain responsible for building a visual model of the world around you.

Your eyes are relatively simple – they just (relatively) faithfully report to your brain how things look, but your brain has loftier ambitions – it doesn’t just want to know how things look, it wants to know how they really are.

One of the ways it does this is basically by doing a white-balance (adjusting for the colour of the illumination so that things look natural), just like a camera. Whenever you look at a scene, you make judgments about the colour and brightness of the ambient light, and you process all the colour information coming from your eyes based on these judgments. In effect you are subtracting the ambient colour in order to estimate the 'true' colour of the objects in the scene.

This gives rise to something called colour constancy. So for instance you see an orange as being orange-coloured whether under artificial lighting or daylight, even though the light from these sources is very different.

So to the dress…

The image is quite a challenging scene for your brain to make sense of – there aren’t really any obvious cues for how to correctly white-balance this image. The source of illumination is not really clear. The other important thing is that blue and gold are complementary colours – that means if you subtract gold from white you get a shade of blue, whereas if you subtract blue you get something like gold or yellow. I think this helps make it more of a binary illusion – you either see one thing or the other.

  • The colours in the dress at the top are actual colours from a screenshot of The Dress. The dresses at the bottom have had uniform but opposite colour corrections applied.

    Credit: Andy Marmery

  • dress colour

    The colours from the dress with different white balances. Credit: xkcd

Basically your brain has to take a bit of a punt, and some people who look at this subconsciously correct for blue and so see white and gold, whereas others correct for gold, and see quite a fairly dark blue and black. The reality is that, if you isolate the colours, it’s somewhere in between, a sort of dirty greyish blue, and quite a dark greenish brown.

I think what makes this such a powerful illusion, is that most people are right on the cusp of going one way or the other – and will often suddenly find that it’s completely changed, and they can’t make it go back – and then think they’re going insane!

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