White Balance

Our eyes and brain work together to see the colors accurately, even though the light source may be very yellow (tungsten lamps) or even green (fluorescent H lamps). The cameras measure the type of color in the scene and balance it accordingly.

We measure color as a "temperature" when the William Kelvin heated a block of carbon. The block glowed in the heat, producing different colors at different temperatures. The carbon block produced first a red light that increased to bright yellow with rising temperature. Eventually the block produced a very bright blue-white glow at the highest temperature.

Also you can imagine an incandescent lamp with a dimmer. When you turn up the dimmer, the voltage increases and the lamp's light is warmer and warmer until it turns red. When the voltage increases, the filament gets hotter and glows more brightly with less red.

The white balance may be automatic or some pre-programmed parameters could be chosen (such as tungsten, fluorescent and even underwater or snow depending on the camera). In more advanced camera it is even possible to calibrate the camera manually. The compact cameras usually have a good white balance, although Canon dSLRs are famous for leaving the scene without adjusting the white balance too much, especially under tungsten lamps.

The three RGB (red, green, and blue) primary colors exist in the light source in varying proportions depending on the color temperature. When the color temperature is high, there is more blue. And when the color temperature is low, there is more red. To the human eye, a white object looks white regardless of the type of lighting. With a digital camera, the color temperature can be adjusted so the colors in the image look more natural. The subject's white color is used as the criteria for adjusting the other colors.

1700 K: Match flame
1850 K: Candle
2800 K: Tungsten lamp (incandescent lightbulb)
3350 K: Studio "CP" light
3400 K: Studio lamps, photofloods, etc...
4100 K: Moonlight
5000 K: Daylight
5500 K: Average daylight, electronic flash (can vary between manufacturers)
5770 K: Effective sun temperature
6420 K: Xenon arc lamp
6500 K: Daylight°
9300 K: TV screen (analog)

Canon cameras have different presets that adjust the color temperature depending on the K of the scene.

In some models there is a custom white balance function to calibrate the camera. There is also a white balance bracketing function.