Colour – 6. Afterimages

In the next few posts I’d like to talk about colour interactions. This is an absolutely fascinating part of the colour theory.

First about the phenomenon of the afterimages:

An afterimage is a type of optical illusion in which an image continues to appear briefly even after exposure to the actual image has ended. We are not normally conscious of this phenomenon, but it is present whenever two shapes meet on a flat surface. To understand it more try the following experiments:

1.

Stare at the black circle for about 20 seconds, and then shift your gaze to the white area within the square, below the circle. The afterimage will appear as a very bright white circle of the same size as the black one. This optical phenomenon is called successive contrast. 

2.

Stare at the black circle again and repeat the first exercise but, this time, when you see the circular white afterimage, concentrate on its outer edge. The afterimage, the bright white circle, will be surrounded by a week but perceptible dark gray aura. (The afterimage of the afterimage.)

 3.

Now concentrate on the black circle and, without shifting your gaze notice the white halo flickering around its edge.

So on the border between two colours there are two afterimages at the same time.

On the darker side of the two squares there will be an even darker stripe of dark colour, on the lighter side an even lighter stripe of light colour. This phenomenon is called simultaneous contrast. (Picture below)

Let’s look at this again with different hues. If I replace the black circle above with a red one, its afterimage has a hue, a complementary to the red: a green one.

If the red circle is placed against an achromatic light gray, the afterimage that surrounds it will contain its complement (green) but will be lighter value than the gray background. Also inside the red circle there will be an afterimage, a thin ring of darker red. (The gray is achromatic, so it influences only the value of the red and not its hue.)

This phenomenon of afterimages play a very important role in colour interaction – which is where I’ll continue next time.