An update to the follow-up. After re-doing the shoot (but with insignificant color-related changes), I've spent the past several hours testing all sorts of permutations of profile generation, using both my chart and a ColorChecker Passport (using all 50 patches, not just the classic 24), the 1.4.0 version of colprof and the one Graeme just posted a link to, adding and removing various patches, and various options to colprof. I made a spreadsheet of a bunch of relevant numerical data, and, in Photoshop, assigned each profile to the original TIFF and visually compared the results. There is one and only one factor that is consistent in improving profile quality, and it's a dramatic one. There is no question, period, full stop, but that adding the following to a .ti3 vastly improves the resulting profile: WHT 96.4220 100.0 82.5210 100.0 100.0 100.0 0.0 0.0 0.0 A significant improvement, but not quite as good, was instead adding a line to the .ti3 of the measurement of the ambient light (which happened to be: X=100.183453 Y=104.100151 Z=90.705105 / L=101.564204 a=-0.319798 b=-3.733409, a value curiously close to D50 white -- coincidence?). Removing the black trap made no visible difference in the results, and only made insignificant changes to the numbers. Adding an all-zero line to the .ti3 moved the black point to the neutral axis, but there wasn't any significant change (though there might be a hint of better detail). All of the preceding applies to LUT profiles. The ColorChecker did not produce an acceptable profile using a LUT. With the ColorChecker and a matrix / shaper profile, there was no visible difference with and without the fake D50 white sample. At a first glance, the results with the ColorChecker are not bad. However, the ColorChecker profile can't properly render the black trap in my chart no matter what I tried, and there are a number of color shifts throughout the range (though luminance is fairly consistent except for the shadows). Still, it might prove acceptable with a bit of manual tweaking under certain non-critical circumstances. Graeme, I think the new extrapolation code needs a bit of work. It didn't always render input white as output white, and there were times when it seemed like there might have been some inversion going on in the highlights. It did do quite swimmingly when fed a profile with an added D50 patch. Oh -- and you hinted at this, but there doesn't seem to be any difference between profiles with and without -u. I'll close with a few attachments: a JPEG with the same values as the original TIFF, tagged with the winning profile (added D50 and black patches, no options to colprof); synthetic versions of my chart and the ColorChecker Passport for visual reference; the two .ti3s (with the D50 white and black lines added at the bottom); and a LibreOffice spreadsheet with my results. Of course, I'm more than happy to supply any other files I have should anybody think them relevant. Cheers, b& P.S. I can't see any difference between either chart in the synthetic or photographed version when doing a blink comparison, which is exactly the end result I desired. b& P.P.S. I just did one more test, merging the ColorChecker Passport .ti3 into the .ti3 from my chart, with both D50 white and black patches. Visually, there was no change and the numbers were slightly worse. The yellow at L22 isn't quite as saturated, for example, but I think that's outside my monitor's gamut and I can't see the difference. It could also be Photoshop to blame. b&
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TrumpetChart!.ti3.D50white0black
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ColorChecker Passport.ti3.D50white0black
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Profile comparisons.ods
Description: application/vnd.oasis.opendocument.spreadsheet