[Gimp-print-devel] Matrix results

[Thomas T. <tt...@bi...>]

Hi dither colleagues,

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.

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

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.

Testing with a greyscale (somewhat fuzzy, jpeg) image with some tiny
text shows that ordered leaves the text sharpest. Ordered also has
highest color noise however around the text edges.

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.

Some problems: color while using the 73 size matrix and adaptive hybrid
and hybrid FS looks out of register. Here it is caused by some dark on
the face pic, lips etc, areas being printed in orange, the cyan moved
away to around the edge of these features.

I just found out I did not use the matrix I wanted to use, but one that
has a bit too much clustering. Bear with me while I generate the correct
matrix and will test again. I doubt the difference will be great.

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'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.


Thomas