Thursday, May 31, 2007
Calibrate Your Camera
To get complete predictability, consistency and control, it's important to calibrate your entire system. We used to do it with film, now we do it a little differently with digital gear.
If you're like most photographers, you've never considered that a digital camera could be calibrated in a similar manner to how you calibrated your film cameras. Now, as then, the process is all about determining how your camera will respond to a variety of lighting situations, so you can generate predictable and repeatable results.
Calibration of a capture system for a RAW file workflow involves these steps: Properly calibrate your monitor to evaluate images on the computer. Create a standard target that contains a gray reference, white and black points, as well as standard color patches.
Establish lighting that mimics conditions for your most common shooting conditions.
Shoot a range of exposures to determine your camera E.I. (exposure index) rating. Identify the best exposure using the most neutral setting in the RAW file software.
Determine the software settings that result in the best match to your target once the file is processed into the desired RGB workspace.
These steps use Adobe software, but the principles apply to any number of software products. I prefer Adobe's applications, as I find they're the most straightforward and detailed in their controls.
Standard Test Target
The most widely used target for color calibration is the Munsell ColorChecker by X-Rite. This target has been in widespread use for at least 50 years in the motion picture and television industries. An ideal test should include this target, a human subject (for real skin tone reference), a black trap, a diffused white highlight reference and some written reference for the exposure.
My test target uses a small cardboard box with a hole cut into it, revealing a black velvet-lined interior for the black trap. The white reference is Styrofoam lens-packing material. The curved form creates a soft ramp from near white to a "clipped to white" tone and allows me to see just how much detail is preserved in extreme highlights.
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