Optical illusion turns blue demon into brunette

Picture uses the negative afterimage effect to magic a brunette into being

It looks like a blue demon. But concentrate, and then look away — and it becomes a much less terrifying brunette.

An optical illusion that changes after people stare at it and look away has taken off on the internet. And, like the dress, it appears that only some people can see the image.

Staring at the picture for about 15 seconds, and then turning to look at a white space, transforms it into something else entirely.

The effect comes from “negative afterimage”, which happens as a result of the way that eyes adapt to images. When the eyes see something — especially something bright — the eyes lose sensitivity, so that those overstimulated parts of the retina can come to resemble their own image.

The reason that the image appears in realistic colours is because the eye processes the image in three different channels: red and green, blue and yellow, and black and white. That means that if the eye is exposed to something very blue, its negative will look beige or yellow.

It’s unclear what makes some see the image and others not. Like The Dress, it may be that the effect is dependent on the make-up of people’s eyes, but it might also be to do with whether people blink enough or are able to keep their eyes still.

The same effect has been demonstrated in other, similar images, and can also be seen in pictures that use the opposite effect to form a positive afterimagine. One such famous picture appears to look like nothing at all —but after staring at it for a while and then looking at something bright, people can see the face of a person that some people say is Jesus.