[argyllcms] Re: request colprof black generation
- From: Martin Weberg <martin.weberg@xxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Mon, 18 Jan 2010 08:14:12 +0100
Thanks, Graeme for digging into this. It will make CMYK-profiling
easier reducing guesswork and iterations.
2010/1/18 Graeme Gill <graeme@xxxxxxxxxxxxx>:
> I think this is more of a bug than expected behavior. The
> curve smoothing filter isn't being forced to transition to the
> start level at white, and the filter may be overly broad.
> Without the smoothing filter you will get an unwelcome
> transition as the black suddenly to kick in though.
Yes, alright.
> After much hacking to do the filtering another way, as well
> as reducing the width of the filter, I get the following:
>
> 90.000000 0.000000 0.000000 [Lab] -> Lut -> 0.113345 0.082260 0.088403
> 0.019597 [CMYK]
>
> but this is right at the transition point, so with smoothing it is
> expected that it not be zero.
K=1.96% much better. However, in my liking, smoothing would start at
the transition point not before.
> 98.000000 0.000000 0.000000 [Lab] -> Lut -> 0.023747 0.016865 0.018471
> 0.001763 [CMYK]
Ok, less "smoothing width".
> A workaround might be to move the start transition up a bit more (say 0.15),
> and reduce the curve shape slightly to compensate.
Yes.
> That seems to be a function of the -L98. Try -L96 for instance,
> and it flattens out (I would guess this is due to the fwd cLUT cell
> based interpolation of the ink limit values introducing an
> inaccuracy, or some other unknown bug). It's nothing to do with the
> target black curve shape though.
Yes, I tried -L95 and enle=.95 before and the curve was ok and thought
the issue I had was gone. Then I tried 98...
Even if -kp was perfect I think the features I suggested would become
nice alternatives. Inputting a function or sequence, like -kf resp.
-ks, K generation would almost be in the hands of the user (depending
on node frequency in -ks). Still, there would have to be some
limitations I guess. Resulting K should not override output
neutrality.
Martin Weberg
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