October 2004 HelpLine
* Understanding White Balance Can Help
You Better Deal With Color In Your Photos
Since this issue is our annual how-to guide, I thought I'd discuss the subject of letters that I receive on a regular basis-white balance. Many readers new to digital have become confused when dealing with white-balance settings on their cameras. If you understand how to use white balance, it can be a helpful tool in capturing better images.
Any explanation of white balance has to start with a discussion of color temperature, which is an attribute of light and is a way of quantifying light's overall, basic color.
The actual term "color temperature" is borrowed from physics, where color temperature relates to the spectrum of light that's radiated from a theoretical object called a black body. As you heat this object, the color that it emits changes. Terms like "red-hot" and "white-hot" are a manifestation of this principle. As an example, if you heat a piece of metal, first it becomes dark red. As it becomes hotter, it turns yellow. Finally, as it's hotter still, it turns bluish white.
The actual color temperature is measured in degrees Kelvin (K). Low temperatures make for warmer light; high temperatures make for cold light.
You also can think of color temperature as the ratio of blue light to red light. When more blue is present, the color temperature is higher; when more red is present, the temperature is lower. For the scientifically minded, the Kelvin scale starts at absolute zero—the temperature at which all classical molecular activity ceases. Zero Kelvin equals minus 273.16 degrees Celsius.