Re: [Gimp-print-devel] Matrix results

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

   Date: Thu, 27 Apr 2000 21:56:07 +0200
   From: Thomas Tonino <tt...@bi...>

   I just put a 73 size matrix in gimp-print in place of the 23 matrix in
   the cvs version. To enable it I replaced all occurrences of DITHERPOINT
   with DITHERPOINT(d, x, y, 4) or similar. Where two DITHERPOINT macros
   were used with a xor, I took one out.

That's an ugly hack, actually, and I think it causes problems.

   Results: my printer prints darker than yesterday (that was with 3.1.3).

I presume you updated MATRIX4_SIZE appropriately?

   Ordered dither does bad for very dark neutral tones. The result is
   splotchy for dark blue/grey, but is fine for dark green. Seems to be a
   problem with black.

I noticed that too.  Dark tans did even worse, with nasty green
splotches.  I don't understand that at all; I would expect ordered
dither to do very well on such regions, and I certainly wouldn't
expect splotches.

   Both ordered and random FS and adaptive random look very sharp. Hybrid
   FS and adaptive hybrid look definitely out of focus. This is all in the
   Photo setting, 720 softweave, Stylus COlor 600, by the way.

Hybrid has some real problems that I don't understand.  I would expect
it to be like random FS, except with better frequency behavior.  But
that isn't the case.

   The results look promising. I wonder where the error diffusion artifacts
   come from. Error diffusion looks so clean, but code turns so complex as
   soon as you make it do the things you want. It does look like a case of
   overflow however.

I believe that.  There are a number of places in the code where things
get awfully close to 2^32, and it's possible that I missed something.
Long long arithmetic is much slower, though...

   I'll try again tomorrow. Then I'll benchmark againt the same CVS version
   that I will be patching. Does anyone have suggestiond for which settings
   to use: My current preference is 720 softweave, Photo, and then use
   Ordered dither and compare to FS Random (favourite it seems). Maybe
   comparing to Hybrid FS or Adaptive Hybrid (hmmm, confusing names :() is
   also a good idea.

I suggest using 1440 highest quality.  720 softweave is fast, but it
shows a lot of banding.  We need 720 to work well (and 360, for that
matter), but for absolute highest quality there's no substitute for
1440.

BTW, how do people feel about random FS vs. adaptive random?  The
adaptive behavior ought to reduce the artifacts in pale regions.

-- 
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