[argyllcms] Re: Colprof feature request: amount of blackpointhuecorrection control

Gerhard FЭrnkranz wrote:
> 
> -------- Original-Nachricht --------
> > Datum: Wed, 13 May 2009 09:48:10 +0400
> > Von: Nikolay Pokhilchenko <nikolay_po@xxxxxxx>
> > An: argyllcms@xxxxxxxxxxxxx
> > Betreff: [argyllcms] Re: Colprof feature request: amount of black 
> > pointhuecorrection control
> 
> > Gerhard, the xicclu uses "simple" gamut clipping by default.
> > When You try xicclu -b -s255 -fb -ir LSM2484.icc, the clipping
> > for relative intent will be by CAM Jab.
> 
> You're right, but I still find it interesting that nearest distance clipping 
> of "absolute black" in CIELAB versus CIECAM space makes so much difference 
> for this particular printer profile.
> 
> -Gerhard
> 
> -- 

No, Gerhard, it's obvious if You'll take a look at profile gamut in both 
spaces. Try this:

iccgamut -ir -pl LSM2484.icm
rename LSM2484.gam LSM2484-pl.gam
iccgamut -ir -pj LSM2484.icm
rename LSM2484.gam LSM2484-pj.gam
viewgam -cr -s -t0.5 LSM2484-pl.gam -cg -w -t0 LSM2484-pj.gam LAB_Jab.wrl
then see resulting Lab_Jab.wrl by VRML-viewer.

You'll see, that nearest to absolutely black point of Lab gamut will be at 
R=G=B=0, but nearest to true black Jab gamut point isn't RGB zero (for higher 
precision use -d4 or even -d3 key for iccgamut if  possible).

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