On Sep 18, 2015, at 12:25 PM, Spinnaker Photo Imaging Center <spinnakerphotoimagingcenter@dnmillerphoto.com> wrote:
Workflow is camera white balanced with what is supposed to be a white target on one side, and black, gray, and white on the other side.
While some white balance targets are more spectrally flat than others, nothing, not even Spectralon, is perfectly flat. Click-to-white-balance relies on a nonexistent physical property. If you know the camera's spectral response and the spectrum of the illuminant, you can predict the correct per-channel scaling factors for white balance without even taking a picture. If you photograph a sample with a known spectrum, you can compare the predicted and actual RGB values to automatically fine-tune the white balance. And if you have a number such samples -- such as with an entire ColorChecker -- you can average them for even greater precision. Of course, this same process will normalize exposure as well.
Comments are made that the x-rite CC is not the same as the pigments in the original art work. Therefore I wonder if this may be an issue?
They're not exactly the same, but, then again, there's variation across manufacturing batches, changes with time and exposure to the elements, and so on. For typical photographic purposes, the differences can typically be ignored. For critical work, you'll want to use your own measurements of your own chart. The original 8x10 cardboard ColorChecker is superb when you want a large, physically thin and flat reference, especially for normalizing white balance and exposure. The ColorChecker Passport is, hands down, the best chart for field use as well as the best small chart for profiling. The extra couple dozen patches on the new half both give you as big a gamut with as saturated colors as you're reasonably going to get with such a device as well as an excellent sampling of the neutral axis. The integrated case gives it as much durability as you can reasonably expect. I've dragged mine all over the Desert Southwest.... The two ColorCheckers serve different-but-overlapping purposes. If I could only have one, I'd easily go with the Passport. I have both and use both. I've made my own charts in the past. Were I continuing to use a profiling workflow based on reflective charts, I'd still use homebrew charts; you simply can't buy anything remotely in the same league as what you can make with a trip to the art store. But that workflow falls quite short of spectral modeling...and, as such, all I need charts for now are to fine-tune exposure and white balance. I can do that with a single patch better than you can with a click-to-white-balance, but it's just as easy to do it with an entire ColorChecker -- which gives negligibly fractional DE accuracy for colors near the neutral axis. Of course, the closer you get to the spectrum locus, other factors come into play.... Cheers, b&