Wednesday, June 27, 2007
Double-Processing White Balance
Whether your goal is perfect neutrality or creating an effect, you can use this technique to refine the colors in your images
Not all white lights are the same. Differences in white light are commonly described by their color temperatures (rated in Kelvin). The lower the number, the warmer the light; the higher the number, the cooler the light. Light temperature has a significant effect on exposure, calibration, printing and display.
The human eye uses the color of white as a reference for all other colors. Assigning white balance accurately is essential to accurate color reproduction. You can only reproduce color accurately if you assign white balance accurately. Once white balance is set, all colors are more accurately reproduced.
While the ability to assign white balance accurately is a useful option to maintain at all times, there will be occasions when you prefer to set white balance expressively. For better or for worse, you can change the mood of an image dramatically by subjectively assigning white balance.
Before digital capture, photographers' options for setting white balance at the point of capture lay in their choice of film, concentrating on camera color filtration and, to a limited degree, development. With digital capture, photographers can set white balance more precisely or expressively, before or after capture, for all images made under a specific light temperature or for individual images, and modify those results indefinitely. The tools are so precise and powerful, it's likely you'll modify your photographic practices to take advantage of these tremendous advances.
Quick Tip >> In Adobe Photoshop Lightroom, the Develop panels can be expanded in size. Doing this enables greater precision when making adjustments.
Setting White Balance In-Camera
Digital cameras allow you to set white balance at the point of capture. They provide a variety of default white balance settings. The Canon EOS system, which I use, typically includes 10: Auto (3000K-7000K), Custom (2000K-10000K), Color Temperature (2800K-10000K), PC-1-3 (personal settings), Tungsten (3200K), White Flourescent (4000K), Daylight (5200K), Flash (6000K), Shade (7000K) and Cloudy (8000K). Kelvins here are approximations.
Auto white balance sets white balance automatically; it works well for a majority of situations. (Camera meter readings may be inaccurate, especially in environments containing multiple light sources of varying types. If you use a studio strobe system, it's likely that a digital camera's auto white balance reading will be influenced by accompanying tungsten modeling lights.) Custom white balance allows users to use an exposure of a white object to create a custom white point setting. You can set white balance numerically. You even can program digital cameras to bracket white balance.