Monday, March 3, 2008
We take a lot of things for granted in digital photography. Matrix metering, auto sharpening, programmed exposure mode, autofocus, we sometimes let the camera do all the thinking for us. Sometimes we let it do too much of the thinking.
I was at a photography seminar recently where the presenter discussed the woes of the auto white balance (AWB) setting on most digital cameras on the market. The setting, like the camera meter, tries to forces color ranges into a standard using an overall evaluation of the scene looking at dark, medium and light tones to gather its recommendation for a white balance to represent the colors as normally as it can. In theory it is a great system, I use it most of the time on assignment but it does have its flaws. It assumes that the scene has a neutral color to base the setting on. And in the real world that just doesn’t happen.
So want to do we do to gauge the proper color balance to render tones correctly? We can set the camera to one of the many presets: tungsten, fluorescent, shade, sunlight to name a few but even those lights vary from bulb to bulb and the sunlight quality changes by time of day. A more accurate way is to gather a custom color balance based on the light you are photographing under using a neutral target. Enter the Digital Calibration Target seen at the top of this posting.
Basically a small disk containing an18% gray middle, and an almost white and almost pure black this card can set your color balance dead on in seconds. To use it you set your camera to manual and take an exposure reading off the card filling the frame with the three bars. When you have the exposure you record an image and check for proper density using the histogram feature of the camera’s playback (you do use your histogram to check exposure don’t you?)
A proper exposure will have three almost completely vertical spikes representing shadows (the far left), midtones (center) and highlights (far right) of the image. You can adjust the exposure so the spikes do not enter touch the edges which is considered ‘clipping” tones.
Now comes the best part. In my Canon 40D I go to the menu and select set a custom white balance. I call up the image of the calibration target and use that image to set the balance. It takes longer to say it than do it and the results are natural color tones. The test I ran is under a harsh tungsten floor lamp whose warm tones shifted the white wall to yellow. Under the custom white balance all tones are natural and do not require post processing in Photoshop for color correction.
The targets aren’t cheap, the 6” mini target I used sells regularly for $75 for two to $129 for a 34’ target. The results are obvious and a good tool for anyone doing portrait work and serious fine art work under a variety of mixed light conditions.