> A white cat on a red background will come out Cyan because the wb corrects > out the excessive red. It shouldn't do if the algorithm is implemented correctly. The simplest Auto-WB method would be to look at the highest R, G and B values in the image, stick them together and call them White: if they ain't equal, adjust the ratio till it is. Sound too simple? Well, probably because it is. Of course, to work quite so simply none of the three channels could be saturated out - so you need some latitude to spare. But such an approach cannot be fooled by the white cat on red background because the red from the background - illumination being equal - CANNOT reflect more red light that the white. It looks red because it reflects proportionately less of the "green" and "blue" parts of the spectrum. Of course, when it could go screwy is when undocumented matrix processing comes into play. Make it complicated: get it wrong in unpredictable ways It could also go screwy if the background was illuminated more heavily. What you really need (IMO) is a good old fashioned Grey Card: point the camera at it with the lights in place, lock in the "observed" white balance and carry on. That's how they do it do I hear? Gotta be better than allowing processors to go wild on a frame to frame basis ;o)
