[argyllcms] Re: White Point

  • From: Hening Bettermann <hein@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sat, 7 Nov 2015 20:28:17 +0100


I have now made target shots with a teflon tape and a black trap. But I can't
figure out how to choose the best-exposed shot.

I use Iridient Developer as the raw processor and PhotoLine for editing. I can
not see how to set the black and white points in Iridient. So I would set these
points in PhotoLine. It allows me to set the readout of the eye dropper to %,
0-255 byte or floating point.

In floating point, the Teflon tape reads 1.000-1.000-1.000. (As does the
whitest patch of the left/upper part of the ColorCheckerPassport; but RawDigger
shows higher values for the Teflon than for the Passport patch). My black trap
reads 0.001. (the black of the Passport, patch D6 in the part which
corresponds to the traditional ColorChecker, reads 0.034-0.035).

The values for the Teflon and the Passport white patch might indicate that the
shot is overexposed. And indeed both Iridient and PhotoLine say so, on a 0.1%
basis. However, RawDigger says otherwise. ??

The Teflon tape shows a gradient in lightness. If I go to the lowest part,
which also is shown as not-clipped in Iridient and PhotoLine, I get different
sets of values. If I choose one of those, where the channel with the highest
value (Blue) is highest, I get values like these:
RGB 0.937-0.979-0.997
I guess I should rather use these to modify the .cie file?

Or need I find a shot that shows NO clipped highlights in Iridient and
PhotoLine? If I do so, the Teflon shows values like 0.670-0.705-0.710. That
seems disappointingly low to me. I can get them a little higher,
0.741-0.777-0.788, but then they are "specular" highlights, where the tape is
bended, so not so diffuse. Also, in this shot, the black trap reads 0.000 x3.
So the blacks are probably clipped.

So which shot should I choose for the profile?

Thank you for your help!

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