Re: [Gimp-print-devel] Halftoning algorithms

[Karl H. K. <kh...@kh...>]

Raph Levien <ra...@ac...> said: 
[ ... ]
> Yep, that's the same me. I'm not working on the gcmm code any more
> because Graeme Gill's libicc is a lot farther along and would appear
to
> kick ass.

I've looked at this as well, and at a bunch of other projects all
trying to do the same stuff. Talk about reinventing the color wheel
again and again and again ... Maybe it's about time to get all the
people working on CM stuff together at one virtual table.

> 
> Of course I've thought about using ICC to do the RGB->CMYK. Let me
> present a few arguments against that:
> 
> 1. The patent situation with ICC is murky at best. EFI owns a large
> stable of patents on "color management" and is eagerly enforcing
them.

That's probably the biggest issue. I am no IP lawyer (and I have
not even seen one on TV :-) so this is probably also the biggest
obsticle.

> 
> 2. There are no free tools for creating ICC profiles. Creating good
ICC
> profiles is hard.

Actually there are. See the end of this message.

[ ... ]
> 
> 4. ICC is not very robust. If you carefully create a profile for a
> printer, then move that profile to a different unit of the same
model,
> or change paper, you basically get the positive effects of the new
> printer plus the negative effects of the corrections for the old
one.
> Thus, it's quite easy to misapply ICC and get poor results.

I know. And that's why I propose a closed loop approach.

You mention the Kodak Q60 target, which is a bit expensive for
just home users. You can get an affortable IT8 targets from 
Wolf Faust: http://www.targets.coloraid.de/ 

Also, there is a free (as in beer) profile editor available at
http://www.abaforum.es/martim/bird/index.htm - unfortunately
it's just for Windows, and so far I was not able to start it under
Wine.

I exchanged some emails with Wolf Faust. He wrote a complete
color management system for the Amiga. This is also free as in beer.
He is working on making it platform independant, but does not have a
lot of time to work on it. So for the same reasons as you, he's 
looking for somebody who could support the development of this free
system. I don't know yet if he's aware of the patent issues.

Another free (now as in speech) ICC based system is at
http://www.abaforum.es/martim/lcms.htm (LGPL). Again, this is just
Windows software and at this time it can only run on x86 processors
because of assembler routines to implement some fixed point math
routines.

What I envision is a closed loop system that does not require a lot 
of tweaking and no expensive tools: You put a standard IT8/7 target 
on your scanner and produce a color correction for you scanner (that's
probably a RGB->sRGB correction just so that the image looks nice on
the screen). Then you print this image without any color correction
(all sliders on default position) using the ink you have installed,
with the paper you usually use, ... This will of course not look
anything like the original. So you put this printout on your scanner
and scan it using the already established scanner correction. Then
some magic occurs and generates the color correction for your 
printer. You do the same once more with the printer correction in
place, do some fine tuning and from there on they lived happily ever
after...

I think all the levers and knobs make the software too complicated 
to the casual user who nevertheless wants some quality output. We
should however leave all these controls in the software so that the
expert user still can have full control over every aspect of the
printout.

How does this sound?

Karl Heinz