[argyllcms] Re: Absolute colorimetric - dark saturated colours excessively light

Alastair M. Robinson wrote:
I was under the impression that the usual gamut-mapping strategy was to sacrifice saturation in order to preserve luminance; the opposite seems to be happening here.

Look at the plain paper version:
http://i14.photobucket.com/albums/a346/robinsonb5/IT8_Plain_Proof.jpg
Device black would be a closer visual match for columns 3 and 4 than what the profile has chosen! 
Hi Alastair,

my understanding is, that Argyll clips to the nearest color on the gamut hull. Are you absolutely sure that DeviceBlack is really closer? Have you verified this computationally?

Btw, Graeme, I've seen, that you have implemented, but not activated, CIECAM clipping in profile. Is there any reason for not activating it?
Here's another soft-proof using a profile generated by Profile Prism, using (IIRC) the Tesco paper:
http://i14.photobucket.com/albums/a346/robinsonb5/ProofPrism.jpg

It's not nearly such a good profile overall (because it's made using a scanner, not a colorimeter), but it does better than the Argyll profiles in columns 2-4.
I had inspected profiles generated by PP, and they seem perform a lightness compression, even for the colorimetric intents, which may be pleasing, but which is acatually not correct and does not comply with the ICC spec, IMO. The colorimetric intents are expected to reproduce all in-gamut colors colorimetrically correct, and to clip only out-of-gamut colors. If you look at profiles generated by other profiles (e.g. ProfileMaker), you'll see that they behave similar as Argyll for colorimetic intent. However, the ICC spec leaves open, _how_ out-of-gamut colors should be clipped, so this is implementation dependent. For a pleasing reproduction with gamut compression, actually perceptual intent is intended.

Regards,
Gerhard

All the best,
--
Alastair M. Robinson


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