gimpprint-dithers
GIMPPRINT-DITHERS(7) Gimp-Print Manual Pages GIMPPRINT-DITHERS(7)
NAME
gimpprint-dithers - Gimp-Print dither algorithms
DESCRIPTION
Gimp-Print includes several dither algorithms. Dithering attempts to
reproduce various shades of gray (or all colors) from only a few dif-
ferent inks (black, cyan, magenta, yellow, and sometimes light cyan and
light magenta). The dots can't vary in darkness or size (except for
certain special printers), and so we need to lay down a certain frac-
tion of dots to represent each distinct level. Different dither algo-
rithms are suited to different purposes, and some are significantly
faster than others.
DITHER ALGORITHMS
Dither Algorithm Description
-------------------------------------------------------
Adaptive Adaptive Hybrid
EvenTone EvenTone screening (experimental)
Ordered Ordered
Fast Fast
VeryFast Very Fast
Floyd Hybrid Floyd-Steinberg
For the highest quality, we recommend use of Adaptive Hybrid dithering.
For continuous tone images, Ordered works just as well and is somewhat
faster. Ordered dithering yields noticeably inferior results with text
and intricate line art, particularly at high resolutions.
EvenTone dithering is a relatively new screening technology developed
by Raph Levien. It offers superior smoothness in highlights and mid-
tones, and increased accuracy in shadows, resulting in significantly
improved results overall. The version of EvenTone dithering that we
are using is enhanced with some additional improvements we have made.
It currently only operates with CMYK (4, 6, or 7 color output) with RGB
input, and should be considered experimental. Note that it is patented
(see US patent 5917614), but it is licensed for use with GPL software.
See http://www.levien.com/patents.html for more information.
Fast dithering, which is a simplified version of ordered dither, is
significantly faster, but color accuracy is worse, particularly on six
color printers and printer using variable dot sizes. On simple four
color printers, the quality is quite reasonable, although color print-
ing will show more speckling in dark tones than Ordered dither. For
single dot size printers, printing grayscale, this algorithm yields
almost identical results to Ordered with some performance improvement.
On three color printers, the results should be very similar to Ordered.
Very Fast is even faster than Fast, with even more loss of quality. It
shows even more speckling, and the output is heavily patterned. On
laser printers, and possibly on certain kinds of text and line art,
Very Fast dithering may actually yield the best quality.
Error diffusion algorithms (Hybrid Floyd-Steinberg is such an algo-
rithm) perform very well at high densities, and are capable of render-
ing very fine detail well, but they tend to exhibit artifacts in the
form of "waves" or "worms" of dots which results in noticeable textur-
ing in pale areas. Furthermore, pale areas immediately adjacent to
white take a while to "build up" sufficient error to print at all.
This is sometimes called "tearing". Its use is not recommended.
COPYRIGHT
Copyright (C) 2001 Michael Sweet (mike@easysw.com) and Robert Krawitz
(rlk@alum.mit.edu)
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2 of the License, or (at your
option) any later version.
This manual page was written by Roger Leigh (roger@whinlat-
ter.uklinux.net)
SEE ALSO
gimpprint-color(7), gimpprint-imagetypes(7), gimpprint-inktypes(7),
gimpprint-mediasizes(7), gimpprint-mediasources(7), gimpprint-medi-
atypes(7), gimpprint-models(7), gimpprint-resolutions(7).
Version 4.2.4 25 Nov 2002 GIMPPRINT-DITHERS(7)
