Hi Michel. If you use icctrans in such way, you are converting from sRGB (v4) to the internal sRGB (v2), and a RGB value of (0, 0, 0) is correctly converted to (0, 0, 0).
You may way to inspect the PCS. icctrans shows teh v2 PCS when using -v But then there are important differences between V2 and V4. If you choose the output profile as a V2 identity, you got: icctrans -t0 -i sRGB_v4_ICC_preference.icc -o*Lab Enter values, 'q' to quit R (0..255)? 0 G (0..255)? 0 B (0..255)? 0 L*=0.0000 a*=0.0000 b*=0.0000 If you use a V4 Lab identity: icctrans -t0 -i sRGB_v4_ICC_preference.icc -o*Lab4 Enter values, 'q' to quit R (0..255)? 0 G (0..255)? 0 B (0..255)? 0 L*=3.1112 a*=0.0000 b*=0.0000 Is that the effect you were expecting? Otherwise a RGB of (30, 30, 30) is converted by PhotoshopCS4 to Lab=(11, 0, 0) which is the same as lcms did. Regards Marti Quoting Michal Soltys <sol...@ziu.info>: > Hello list.. > > > If I understand v4 specs (and related documents) correctly, perceptual > intent in v4 profiles should re-render to PRMG (at profile build time, > so generated LUTs take into account intermediate reference gamut), or at > the very least scale white and black points to PRM's white and black > (and then "cooked" to D50 illuminant, as in relative colorimetric approach). > > But, for example if I execute (with v4 profile downloaded from > http://www.color.org/srgbprofiles.xalter): > > icctrans -v -w -t0 -i sRGB_v4_ICC_preference.icc > > Then for RGB=0,0,0 - the PCS values are all 0 (and considering PRMG's > black point - they shouldn't be ?). > > I also tested the above with -t1, and I'm not really sure what to make > out of both PCS and destination profile values: > > icctrans -v -w -t1 -i sRGB_v4_ICC_preference.icc > > R=29.21 G=29.28 B=29.23 > X=1.2054 Y=1.2512 Z=1.0315 > L*=10.9191 a*=-0.0312 b*=0.0117 > > L* looks rather extensive for a PCS value, and RGB in destination > (internal sRGB) profile seems to follow it. On the other hand - XYZ > values seem perfectly fine. > > Anyway - some hints of what I'm missing or misunderstanding would be > welcome (icctrans from lcms 1.18a). > > > > ------------------------------------------------------------------------------ > Register Now for Creativity and Technology (CaT), June 3rd, NYC. CaT > is a gathering of tech-side developers & brand creativity professionals. Meet > the minds behind Google Creative Lab, Visual Complexity, Processing, & > iPhoneDevCamp asthey present alongside digital heavyweights like Barbarian > Group, R/GA, & Big Spaceship. http://www.creativitycat.com > _______________________________________________ > Lcms-user mailing list > Lcms-user@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/lcms-user > ------------------------------------------------------------------------------ Register Now for Creativity and Technology (CaT), June 3rd, NYC. CaT is a gathering of tech-side developers & brand creativity professionals. Meet the minds behind Google Creative Lab, Visual Complexity, Processing, & iPhoneDevCamp asthey present alongside digital heavyweights like Barbarian Group, R/GA, & Big Spaceship. http://www.creativitycat.com _______________________________________________ Lcms-user mailing list Lcms-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lcms-user
