How the Eye Sees Light (2)
Since the camera doesn't have a brain, it needs help to compensate for color temperature changes.
Filters
One thing a camera can do to compensate for changes in color temperature is to use filters. Most cameras have a built-in filter wheel. This is a device that will allow you to place one of several filters between the lens of the camera and the beam splitter. Most cameras are set up to operate with TV studio lights, which have a color temperature of 3200° K. If you go outdoors to shoot, you will change the filter wheel to compensate for the change of color temperature.
Black Balance
Changing the filter wheel is only the first step. Because clouds, shade, reflections, and other conditions all have an effect on color temperature, you will have to balance your camera every time you set it up in new lighting conditions, which is simply establishing the proper color combination for given lighting conditions. The first step is to black balance the camera. Black balance ensures that there is no color information and that each of the color channels is set at 7.5 (for NTSC, 0 for PAL). The next step is to white balance the camera.
White Balance
To white balance a camera, simply aim and focus it on a white card and push the white balance button. The electronic circuitry of the camera will then adjust its light reception so that the green CCD produces 59% of the picture, the red CCD produces 30%, and the blue CCD produces 11% (see previous discussion). Since the camera is now properly mixing the three primary colors, the rest of the color spectrum will be fine.
Color TV camera, showing location of filter wheel.