[argyllcms] Re: camera profiling with newest version of Argyll

  • From: Ben Goren <ben@xxxxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 27 Aug 2015 16:47:34 -0700

On Aug 27, 2015, at 4:20 PM, Chad Johnson <chad.chadjohnson@xxxxxxxxx> wrote:

How are you converting from XYZ to RGB?

The calculator on Bruce Lindbloom's site:


That depends upon the illuminant, no?

Yes, but D50 is used as the illuminant for almost everything in colorimetry,
including PCS calculations. If a reflective surface clips with D50, it can only
be because of fluorescence. An object with uniformly flat 100% reflectivity
will have R=G=B=100%.

Just to be clear I am not setting the WB from that patch. Or any patch for
that matter -- it's set from shooting a gray card and then I check it against
one of the grey patches on the Color Checker.

Then I really have to wonder what's going on...because that file has neutral
RGB values for something that's decidedly not neutral.

Part of the complication could again lie in the fluorescent light you're using;
the plot you posted, if I remember right, showed it was strongly filtered in
the UV (as one would expect). That means that there'll be an especially strong
metameric shift with that patch -- it'll be much bluer when viewed in daylight
than with your fluorescent light. How all that would come out in the wash...I
wouldn't want to guess without running numbers.


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