Re: [Gimp-print-devel] Epson 870 shot 2 (sorry)

[Robert L K. <rl...@al...>]

   Date: Sun, 21 May 2000 01:25:40 +0000
   From: Jean-Marc Verbavatz <ver...@if...>

   Again, I've put my files (print.h, print-escp2.c and print-dither.c) at
   "ftp://perse.saclay.cea.fr/pub/incoming/verbavatz" for testing and comments.
   They're based on the version of May 18th of gimp-print. Robert, I knew you
   couldn't help playing with dithering but I understand that :)

It appears to me that you've generalized the range stuff somewhat, so
a given value can be covered by multiple ranges.  Good.

I like it (at 1440x720 highest quality).  There are a few issues,
though:

1) There's still the yellow-green cast.

2) I think that the value you've assigned the light colors (lc and lm)
is too high.  This results in their receiving too much credit for ink
printed, which leads to an overly sharp transition between light and
dark.  I think that this is the source of the yellow cast, actually;
in midtone areas, not enough dark magenta and cyan is used, so the
yellow is too prominent.  My last try suggested that .22 was a good
ratio.

   I've compared the rendering with the current repository (from May 19th) and:

   - it looks a lot better to me as far as grain and dithering is concerned.

The problem I'm seeing there is that there are a lot of regions of
fine horizontal lines, like an ordered dither.  I haven't tracked down
where that's coming from.

   - the density is much lower. This is because my color values are
   quite different. I've tried to work out each of them separately so
   that they would give the same output (on my printer). I think the
   current repository yields a much lower gamma because values are
   decreasing (from darkest to lightest) much faster than what I've
   done. I believe we should just set a higher density for this
   printer instead.

Density and brightness/gamma are two different things.

   - I have, from what I've seen, a better balance between light and
   dark inks, at least at higher qualities, which should increase the
   lifetime of cartridges.

That's always good.

-- 
Robert Krawitz <rl...@al...>      http://www.tiac.net/users/rlk/

Tall Clubs International  --  http://www.tall.org/ or 1-888-IM-TALL-2
Member of the League for Programming Freedom -- mail lp...@uu...
Project lead for The Gimp Print --  http://gimp-print.sourceforge.net

"Linux doesn't dictate how I work, I dictate how Linux works."
--Eric Crampton