[argyllcms] Why colprof doesn't generate identity profile for synthetic image?

  • From: Mikhail Matrosov <mikhail.matrosov@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 28 Aug 2012 18:40:16 +0400

I have a synthetic image of the ColorChecker (see the attachment, or here
"Derived from GretagMacbeth L*a*b* D50 data, sRGB":
All colors are exactly the same as specified in ColorChecker.cie file,
after conversion from Lab to sRGB using Bradford adaptation from D50 to D65.

I have this synthetic chart in ColorChart.tif. I run the following:

scanin.exe -dioap ColorChecker.tif ColorChecker.cht ColorChecker.cie

I see that all the patches are located properly on diag.tif. I then run:

colprof.exe -v -y -qh -bn -ax -U 1.0952  ColorChecker

It says that peak error is less than 0.01 deltaE. I apply the profile using
tifficc.exe and the result file differs from the source no more than on 1-2
RGB points. But when I apply the same profile to the image with all RGB
colors, I see significant difference, about 10-15 RGB points.

Why? What arguments should I use with colprof to obtain an identity
profile? I don't want my profile to spoil a "perfect camera". How to
achieve that?

Best regards, Mikhail Matrosov

Attachment: ColorCheckerMini_sRGB_from_Lab_D50.png
Description: PNG image

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