[argyllcms] Re: Difficulty shaping Black ink curve for CMYK profile
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Mon, 10 Dec 2018 12:32:40 +1100
Samuel Chia wrote:
Hi,
I've noticed that doing more severe concave curves tends to result in a kink
at the black
end point. This kink is always at the 90% point. Here is a link to the
screenshot of the
curve preview generated by xicclu.
https://drive.google.com/file/d/1UE-DaCallwUTQjVS-1qrV53NEyM3TuTa/view?usp=sharing
yes, the range of control is not idea, but the interactions of black level and
resulting ink combinations is not that intuitive, so it's a challenge to provide
controls that would be easy to use.
The graph you show looks pretty good as such things go. Are there actually any
visible artifacts in the printed result ?
Interestingly, the white end of the curve never develops any kinks regardless
of the stle
and stpo value for any shape parameter between 0.0 and 2.0. It only and
always affects the
black end.
Because that is where there is most choice about ink composition. There is no
choice
at white.
When reducing the concave-ness of the shape to ~0.8, the kink is virtually
gone. Perhaps
this curve's spline turning point is hardcoded and I'm wondering whether it
might be
possible to get a smooth gradual transition to dmax whilst enforcing a more
concave shape.
The curve is as plotted in the documentation. The interaction depends on the
characteristics of the printer though. Without having the profile to play with,
it's hard to make any suggestions. One thing you might try though, is slightly
reducing the maximum K value (-L parameter - i.e. try something between 90 and
100%).
Cheers,
Graeme Gill.
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