Hi Marti I saved the sRGB input profile and see I'ts labelled as V4.2. So, what's the logic followed by LCMS? Something like, if no Black Point is defined assume it's X=Y=Z = 0 and scale that to be L*=3. Otherwise scale the Black Point.
Is there a way to make LCMS2 behave like LCMS1 or will it always perform Black Point Compensation? The reason I ask is I intend to compare some LCMS transforms to current code that uses Apples ColorSync API. I do not think ColorSync is doing BPC. Best regards Mark On 06.06.2010, at 19:16, marti.ma...@littlecms.com wrote: > > Hi Mark, > > That's black point compensation, V4 perceptual and saturation > have non-zero black points. sRGB built-in is basically a V2 > profile, so for going from V2 black (which is zero) to v4 black > (which is about L*=3) we need some sort of scaling. > > Regards > Marti > > > Quoting Mark <d...@cine-scan.com>: > >> Hi Marti >> >> looking at the stages created for a sRGB -> XYZ transform I see 3 stages are >> generated >> - curve set stage for the gamma curves >> - matrix float stage converting device rgb to xyz (I see the matrix is >> scaled so by 1/MAX_ENCODEABLE_XYZ) >> - a second matrix including offset: >> Offset: 0.0016800256 0.0017365765 0.0014350219 >> Matrix: 0.9965152458 0.0000000000 0.0000000000 >> 0.0000000000 0.9965269000 0.0000000000 >> 0.0000000000 0.0000000000 0.9965207904 >> >> Can you tell me what the second matrix stage does? >> The matrix varies according to the intent passed creating the transform. The >> data above is for INTENT_PERCEPTUAL and INTENT_SATURATION (IIRC). >> INTENT_ABSOLUTE_COLORIMETRIC uses other values, without offset. >> INTENT_RELATIVE_COLORIMETRIC does not have this second matrix stage. >> >> Best regards >> Mark >> ------------------------------------------------------------------------------ >> ThinkGeek and WIRED's GeekDad team up for the Ultimate >> GeekDad Father's Day Giveaway. ONE MASSIVE PRIZE to the >> lucky parental unit. See the prize list and enter to win: >> http://p.sf.net/sfu/thinkgeek-promo >> _______________________________________________ >> Lcms-user mailing list >> Lcms-user@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/lcms-user >> > > ------------------------------------------------------------------------------ ThinkGeek and WIRED's GeekDad team up for the Ultimate GeekDad Father's Day Giveaway. ONE MASSIVE PRIZE to the lucky parental unit. See the prize list and enter to win: http://p.sf.net/sfu/thinkgeek-promo _______________________________________________ Lcms-user mailing list Lcms-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lcms-user
