The reason we need to adjust the colors reorded by the camera is because the scene we are photographing may be lit by different light sources and the variation in light sources may cause a color cast in the final image, the color cast which a light source may exhibit is determined by the color temperature of the light source. The unit of measurement for color temperature is Kelvin (K).
Various light sources are approximately categorised with color temperatures as follows:
- 1700-1900K, Match flame or candle light
- 3000K, Warm fluorescent light
- 3000-3300K, Incandescent light bulb
- 3200K, Sunrise or sunset
- 3400K, Photo flood light
- 4000K, Moon light
- 5500K, Sunny daylight around mid day
- 5500K, Electronic photo flash
- 6000K, Overcast sky
- 7000-8000K, Summer shade
The above diagram shows the effect of color temperature changes with differing colored light sources.
As the color temperature changes from daylight to the low end (candle light) the color cast will gradually move to a red cast and as the color temperature moves from daylight to the higher end the color cast will gradually move to a blue color cast.
The camera control for white balance to correct the color cast will need to be adjusted to match the color temperature of the light source illuminating the scene. Generally most cameras will control white balance automatically and some cameras will do this better than others. Many cameras will also have a manual control for white balance so that the user can select the actual color source illuminating the scene.
Generally a slight blue cast in a picture will give a cooler feeling to a picture and a slight red cast can give a warmer feeling to a picture. Some photographers may wish to give the image a slight cast in such a way that it enhances the image. The following images show the effect of three different camera settings of white balance and the resulting images. These images are taken in daylight with different in camera white balance settings.