What Is White Balance and How Does It Work

The problems photographers have with how the different colors of light affect their pictures have been with us ever since color photography was invented in the late nineteenth century. In traditional film photography, colored gels would be placed in front of lights, or filters would be put on or behind the camera lens, to try to bring all the various light sources into balance with each other. It was meticulous work, during which the photographer would take frequent meter readings to determine the precise color temperature of the light. Once proper color balance was attained, she could then push it toward one end of the spectrum or the other, as an artistic choice, such as giving a portrait a warm (rosy) glow.

One vexing problem was color consistency. Because color dyes used in film (for that matter, color dyes used in virtually every other material) are inherently unstable and virtually impossible to manufacture so that every production run will be exactly like the one before or after it, photographers never could depend on film to always react to light—and therefore reproduce color—in exactly the same way every time. This was true even when we bought only certain brands, speeds, and types of film. Like most other professional photographers, we bought our film in bulk quantities and stored what we didn't use immediately in the freezer, thus ensuring that each roll we shot was manufactured at the same time, using the same dye lots. When we finally ran out and had to buy more film, it was inevitably from another emulsion lot. This meant that we had to retest it, measuring color temperature and adding gels or filters, until we found the new batch's proper color balance. Precision color has never been for the faint of heart or shortcut takers.

The white balance tools of digital cameras (and their cousins, camcorders and digital camcorders) take much of the time and effort out of this painstaking process. To attain proper white balance, a digital camera analyzes a scene and attempts to determine what areas should be truly white. The operating theory is that if there is, for instance, a 5 percent green shift in the white areas, the rest of the picture probably has too much green in the same percentages. So, subtracting 5 percent of green from the entire picture would (so the logic goes) remove any color shift.

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