When you look at a white sheet of paper in any light it always looks white. That’s because your brain automatically compensates for lighting irregularities. Regardless of the existing lighting conditions, unless you really think about it, white always appears white. Whether under candlelight or sunlight, fluorescent or tungsten lighting, sunset or noonday, a white sheet of paper will always appear white because our brain retains what color science refers to as “memory colors.”
Our brain compensates for almost every color of light, and delivers a believable impression of color neutrality. Memory colors are logged into our brain from childhood. Memory colors include: grass (green), sky (blue), paper (white), orange (orange), etc. No matter when we see these memory color items, our brain registers these colors and in a sense, overrides the actual color as rendered by existing light.
Unfortunately this is not true for (digital or film) cameras. To the camera, every slight variation in lighting changes the color and/or brightness of what we call “white.” The color of light is measured by a temperature system called Kelvin; named after the 19th century British physicist who introduced the measurement scale of temperature. The Kelvin system measures light temperature that range from 0 to 10,000, with white light (equivalent to sunlight at noon on a sunny day) measuring 6500°K.
This same white paper that our brain “sees” as white (regardless of the lighting condition) is almost always seen by digital cameras as slightly colored. This phenomenon is why most digital cameras and imaging software include “white balance” tools. An image’s gray/white balance is the single most critical issue in color image processing, and absolutely must be addressed before images can be printed correctly. The white balance tools in both camera and printers are covered in significant detail in my Correct Color book.
