[argyllcms] Re: Scaled Rec709 TRC question

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sun, 20 Feb 2011 21:15:00 +1100

János, Tóth F. wrote:
I managed to apply CIECAM02 transform on the colors. (This is very slow when
compared to the standard color transfer but that is another problem...)

You wouldn't use the CIECAM02 code on pixels. Use it to setup a fast

Now, how should I set up the CIECAM02 view condition parameters (for lcms)
to match with ArgyllCMS (as close as possible)?

I currently set these values for the source:
vc1.Yb = 20;
vc1.La = 100;
vc1.surround = 1;

The dispcal has a variety of source conditions that depends on the
assumed/guessed source viewing conditions.

Rec709 and SMPTE240M are assumed to be bright studio situations
of 1000 Lux == 318 cd/m^2.

I used the same values for all the three ambient light presets except
the vc2.surround which is 2,3,4 for Bright,Dim,Dark

I set the Adapting/Surround Luminance to 20% of the ambient luminance,
with the Luminance of white in the Viewing/Scene/Image field set to the
luminance of the display.

See dispcal.c about line 3732.

I think they should be 1,2,3 and I should change the Yb and/or La values.
(The lcms documentation is very close-mouthed about CIECAM02. It doesn't
even explains what these parameters means and I could find as many symbols
as many times I used google to find some informations about this...)

I've put some notes in the Argyll CIECAM02 implementation. See

There is also an illustration in the tutorial I did for
the FOGRA Colour Management Symposium 2010:
Page 49.

Graeme Gill.

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