[argyllcms] Re: ArgyllCMS V1.2.0 has been released

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 03 Aug 2010 23:17:13 +1000

Alastair M. Robinson wrote:

/path/to/1.2.0/bin/colprof -cmd -dpp -S <srgb> 120_md 
/path/to/1.2.0/bin/colprof -cmt
-dpp -S <srgb> 120_mt

Note the minimal difference between 120mt and 120md - and that 120md is 
marginally the
darker of the two.

Hi,
        I'm not sure precisely what the explanation is, but some experiments
using collink -ir rather than colprof perceptual lead me to (handwavingly) 
explain
it this way: The purpose of the perceptual or saturation gamut transform is to
basically morph the source gamut into the destination gamut. Changing the
viewing conditions changes the shape of the gamut, but a perfectly operating
gamut mapping will simply adapt to the different shape and map to the same
destination gamut. ie. the gamut mapping tends to cancel out changes
introduced by the change in the viewing conditions. My speculation would
therefore be that V1.2.0 shows less difference because the gamut mapping
is more accurate than V1.1.1 :-).
Of course any changes within the source gamut (rather than changes affecting
it's shape or volume) introduced by differing viewing conditions are probably
not counteracted by the gamut mapping, so some changes will still be evident.

[The collink -ir experiment confirmed that there is no change at all in
 the CIECAM02 behaviour between V1.1.1 and V1.2.0. The difference you notice
 must therefore be a property of the change in gamut mapping. ]

Apart from that the new mapping is impressive, and looks like it'll be well 
worth the
vastly increased calculation time!

Yes, the performance change is unfortunate, but my priority was to "do it 
right",
and worry about performance another time.

Graeme Gill.


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