The „Human White Balance“ in the Brain
Human visual perception does not work like a technical measuring instrument that projects signals from the eyes on some kind of „monitor“ in the brain. The pictures we perceive are created in the brain and after the brain has compared the signals from the eyes with known patterns and colors.
This process is highly complex and not fully understood. But one aspect that is certain is that the color perception tends to be adjusted towards known pictures and therefore variations of color because of different lighting are partially or even completely compensated by the brain.
This is the reason why the the sample picture from the previous page, taken under candlelight appears more orange on the photo than in „real“.
Additionally the adjustment of color perception in the brain works differently for different areas of an image, that is something no digital camera can do so far.
Please see this snapshot from a skiing vacation (click for a larger view):
Watch how the snow on the right hand side, lit by sunlight, appears very neutral as a plain white – no problem for the automatic white balance of the camera.
The snow in other parts of the picture, more or less in the shade is not only darker but also colored blue. The human brain manages to give you the impression that the snow is white everywhere when you see such a scene in reality.
On a picture you can eliminate such color casts only in more complicated image processing, with a person deciding which parts of the image need which correction.