The perceived color of an object is affected by the color of the lighting under which it is viewed. The human brain is capable of detecting and compensating for such changes in perceived color. As a result, a white object will appear white to humans whether it is viewed in sunlight, under overcast skies, or under incandescent or fluorescent lighting indoors. To achieve a similar effect, a digital camera must emulate the human brain and adjust colors accordingly to the lighting, so that colors that appear white when viewed directly also appear white in the final photograph. This adjustment process is known as “White Balance”.Most video systems employ a “white balance” feature to help overcome color problems created by adverse lighting conditions. The color balance assumes that under normal conditions, if a white object can be made to appear white, the remaining colors will also be accurate. However, if the original lighting is not close to the proper color temperature (typically daylight), the “white balance” may reproduce white at the expense of other hues.Most digital cameras feature automatic white balance, which means the camera analyzes the overall color of the image and calculates the best-fit white balance. However, these systems can be easily fooled, especially when taking a photograph dominated by a single color, such as green. Modern “prosumer” digital cameras also allow “white preset”, which involves measuring the white point from a white sheet of paper or card (or a nearby wall). The camera then records that temperature and uses it to correct all subsequent images until the setting is reset.
