color constancy

Somebody asked why digital cameras can’t accurately portray color, and I answered:

It’s not that digital cameras can’t portray color, it’s that images are different from scenes. Images can’t properly portray scene color. When you look at a scene, the colors that arrive at the back of your eyeball depend on the color of the visible objects and the color of the light falling on them. But for practical purposes you usually want to perceive the colors of objects (“color constancy”), so your visual system makes a mighty attempt to subtract out the color of the illumination. When you look at a paper photograph, the colors of the photographed scene are now represented as physical colors on the paper, and the illumination that your brain is subtracting out is the light falling on the paper. Due to color constancy the two situations, looking at a scene and looking at a photo, are intrinsically different, and you cannot say whether the colors in the photo are “accurate”. What the question even means is open to interpretation.

original version, November 2009
added here March 2011