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Subject: Re: raw 3.1 professional custom profiles for highend digital cameras

The reference data values for the 24-patch color checker used in Tom Fors script were provided by me. They are averaged from spectral measurements from approximately 50 different physical samples of the Color Checker. The standard deviation is quite small, and is generally below the granularity that Photoshop's integer-based implementation of Lab allows. I've run experiments where I compared the results of the script with manual adjustments that take measurements of the specific ColorChecker being shot as their aim point, and I can tell you with a high degree of confidence that unless your Color Checker has been subjected to very unusual wear and tear, the reference data in the script is more than adequate.

The purpose of the script is quite limited. Its sole purpose is to adjust the R, G, and B primaries of the built-in Camera Raw matrix profiles to account for unit-to-unit variation in the cameras. (Depositing RGB filters a few microns thick onto a chip is an inherently variable process, and is responsible for much of the unit-to-unit variation.)

A single, static camera profile is, in my experience, useless for just about anything except the image of the target used to build the profile, and other images taken under identical lighting conditions. I certainly get more accurate color from Camera Raw than I do from a custom camera profile built using ProfileMaker Pro and the ColorChecker SG.

There's a fundamental mismatch between ICC profiling technology and digital capture. ICC colorimetry is output-referred. We need scene-referred colorimetry. The Camera Raw solution to this fundamental issue is, in my view, brilliant. For each supported camera, Camera Raw contains two matrix RGB profiles, one built under Illuminant A, the other under D65. (The profiles were built by Thomas Knoll using his own proprietary profiling tools, which I suspect are better than anything on the market if the CMYK profiles bundled with Photoshop are any indication.) The white balance controls interpolate between (and extrapolate beyond) these two profiles.

The two huge benefits of this approach are

1.) It works under all lighting conditions, which a single ICC profile does not.

2.) It preserves accurate relative hue and saturation while allowing me to impose my own tonality, which is a great deal more useful to most photographers than a single LUT-based profile that compresses the scene dynamic range into the output dynamic range the same way for all images, whether of a polar bear in the snow or a black cat in a coal cellar.

There are many raw converters that allow you to use a custom camera profile built by ProfileMaker or its competitors. If that's really what you want, I suggest you use one of those. But this is an approach that would cripple Camera Raw, and I would argue strenuously against it. I doubt that Thomas would go for it anyway, for all the aforementioned reasons.


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