[argyllcms] Re: Black generation and black ink limiting

  • From: Nikolay Pokhilchenko <nikolay_po@xxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 30 Mar 2010 01:21:57 +0400

Fabrizio Levati wrote:

> Using always the same source data and -kp parameters and then adding a -L92, 
> I end up with roller coaster shaped curves as shown in the attached pictures. 
> Even if we are in the "far black" region I'm not so sure this kind of curve 
> won't have any consequence on the resulting separations.
> Graeme told me, during the FOGRA symposium, that maybe Argyll is not the best 
> choice if you need very smooth curves but actually, the smoothness is 
> acceptable if you don't use any black ink limit...
> What am I doing wrong?

It's hard to tell without having the chart data. The main reason is the device 
behavior at the gamut boundary, that is limited by ink limits. For certain 
device, the Argyll black curve "native" shape at the right edge of graph 
-kp_0_.3_.9_.9_.7_-l220_-L92.png isn't optimal at all. The black curve tends to 
go higher, than it allowed by -L92 limit. May be You choose inappropriate 
parameters for kp. So You should try to lower the right "aim point" for the 
black, for example "-kp 0 .3 .9 .86 .7 -l220 -L92". When the black curve will 
approach the right side not from the top, but from the bottom, the CMY "bump" 
may disappear, IMHO. Conversely, the improvement may happen by raising the 
right aim point for the black.
If it's impossible to achieve the smooth curves, may be the black generation 
algorithm shall be improved.

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