Re: Darn you, stochastic dithering! I shall be avenged!

   From: "Andrew A. Gill" <superluser@xxxxxxxxxxxxxxx>
   Date: Tue, 20 Jul 2004 21:37:08 -0400 (EDT)

   Does anyone know how to turn off dithering with gimp-print 4.2.5
   and the pcl-900.ppd on an HP Deskjet 940C?

   I've got an image that I want to make photocopies of, so I
   pre-halftoned it, but whenever I try to print it, the output
   obviously has been stochastically dithered.  This dithering is
   very low-contrast, and will make it difficult to reproduce on
   low-quality copiers.  I have the following options in the PPD
   file, and they appear identical to the options that I get when I
   try to print in GIMP 2.0:

   Adaptive Hybrid
   Ordered
   Fast
   Very Fast
   Hybrid Floyd-Steinberg
   EvenTone

   There is no option for ``no dithering.''

You can probably do it by setting the density to 2.0 and making sure
that you're always sending either 0 or 255, but this won't entirely
work at high resolution (use Very Fast dithering).  You'll find it
easier in 5.0 beta; use Manual Control for image type and print
quality and Very Fast dithering.  You then have two choices: use Raw
color correction (which does no density correction) and send either 0
or 255 for each pixel, or use Threshold color correction and set
density very high (you can set density as high as 8.0 in 5.0).

If you think about it, "no dithering" doesn't really make much sense;
if you send levels other than 0 or 255, the driver has to dither it
somehow.  The real problem you're running into is the density
correction (to avoid over-inking the paper); that limits the maximum
level to something less than 100% coverage.  Raw color correction
bypasses this by not doing density correction at all.

Perhaps we could add a "Pre-dithered" color correction, which would
combine raw and threshold.
-- 
Robert Krawitz                                     <rlk@xxxxxxxxxxxx>

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

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


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