[argyllcms] Re: sRGB.icm changed in Argyllcms 1.6.1

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 31 Dec 2013 13:38:50 +1100

Elle Stone wrote:
> The XYZ values in the Argyllcms profiles sRGB.icm changed in Argyllcms 1.6.1, 
> compared to
> 1.6.0 and previous versions of Argyllcms.


Yes, I switched to working from the sRGB specification x,y values rather
than the pre-computed matrix values given in the sRGB ICC profile paper,
to bring it into line with the way all the other reference profiles
are created, and (hopefully) improve it's conformance to the spec.,
which I think is achieved.

> The Argyllcms 1.6.0 and previous sRGB.icm profiles are color-balanced to the 
> 6 decimal
> places that xicclu displays:
> /usr/local/argyll/argyll160/ref $ xicclu -pl -s255 -v0 sRGB.icm
> 255 255 255
> 100.000000 0.000000 0.000000

Hmm. I'm thinking that this may have been accidental, or perhaps the
pre-computed values had been tweaked slightly.

> The version from 1.6.1 and 1.6.2 isn't color-balanced to 6 decimal places:
> /usr/local/argyll/argyll161/ref $ xicclu -pl -s255 -v0 sRGB.icm
> 255 255 255
> 100.000000 0.000000 0.001233

This is a result of quantization the primary XYZ values into the ICC 15.16
fixed point format.

I will changed the code to minimize the error in the sum of the quantized
primary values, which should reduce the white point error at a cost of
increasing the primaries errors slightly.

The resulting sRGB profile is here <http://www.argyllcms.com/sRGB.icm>

Graeme Gill.

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