[argyllcms] Re: How does the targen do the black generation withpre-conditioning profile?
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 22 Aug 2008 16:30:02 +1000
Nikolay Pokhilchenko wrote:
Graeme Gill wrote: There is no black generation for the targets. They explore
the CMYK
space - ie. it's a 4 dimensional characterization of the device. Black
generation is
done in the profile creation of the B2A tables.
But how does the targen do the patch distribution, for example with both -c and
-I
keys?
There are a variety of different distributions, that's really the point
of a lot of those options. There is a brief description in the documentaton:
<http://www.argyllcms.com/doc/targen.html#f>. The -c parameter is used for
some of the distributions, and not for others. The way -I is handled depends
on the type of distribution, some being able to work within the device gamut
naturally, and some needing to used cruder methods such a rejection testing.
It seems to me, targen computes grid for device space in Lab(?), then lookups
the
CMYK value in B2A table from given pre-profile. It is right?
No, it depends on the distribution chosen. For the -m points, the grid is in
device space (ie. a 4 dimensional hyper-cube grid for CMYK).
When I want to generate
ADDITIONAL qualifying chart, I'd like get patches closer to desired black
generation
method. I don't interesting in whole 4-dimensional supplementary
characterization,
because many of full-4D patches almost useless, since I already take shape for
black
generation.
I don't think there's an easy way to do that, although if you went to
enough trouble you might manage it. For instance, one way might be
to create an sRGB -> output device link using -G with saturation intent,
generate test points in RGB space, then map them to the output CMYK
using icclu. Those points could then be edited into the .ti1 file.
Of course, it's reasonable when black generation chosen will not be changed
aftertime, including device link. May be it worth to add one more targen feature:
"Use
pre-conditioning profile black generation" with standard for black generation
parameter
set, i.e. -k, -K, -L? That feature will allow to get more precision profiles by
the
less overall patch count.
Maybe, although there are some other features in a similar vein I'd add first,
such as being able to target test points at a particular L*a*b*, say the grey
axis. Additionally, I think it would be better to add full two pass N channel
separation support, which could be used for CMYK, and would achieve the
same result with a lot broader application.
Graeme Gill.
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