04.03.2006 12:00 AM
Color Balancing Your Camera
While it would be nice if a video camera could be calibrated at the factory to always reproduce color exactly as it appears to the human eye, that’s not going to happen. There are two color-balance problems that even the most sophisticated camera cannot automatically overcome: One is that the color of the light under which images are captured varies according to time of day, sun or shade, the type of bulbs used in electrical fixtures, as well as a number of other lesser factors. The other is that a powerful computer known as the human brain automatically compensates for these variations so that the eye sees the same color under a variety of lighting conditions. This is something the camera simply cannot do.
The white balance control allows videographers to get the same consistency in color reproduction from their video cameras as they do with their eyes. Understanding how your camera's white balance circuit works is the key to avoiding orange faces and blue landscapes.
All cameras, including those with only a single imaging chip, use a combination of three-color channels when processing an image. The intensity or output level of the signal for each channel corresponds to the amount of red, green or blue in the subject. The key to consistent color is to understand that, as far as the camera is concerned, white occurs only when the levels of all three channels are exactly the same.
When you press the white-balance button on a camera, you are instructing the camera to examine the level of the brightest part of the scene, which is presumed to be white, and turn the output of the red and blue channels up or down until they are the same as the green. This is somewhat akin to adjusting the balance control on your home audio system so the music is centered about you even if you are not sitting in the center of the room. Point the camera at a white card, press the button, and you’re all set. Or are you? In the next Sharpshooters’ Tip we’ll explore how to avoid some common white balancing errors.