GIMPPRINT-DITHERS(7) Gimp-Print Manual Pages GIMPPRINT-DITHERS(7)NAMEgimpprint-dithers - Gimp-Print dither algorithms
DESCRIPTION
Gimp-Print includes several dither algorithms. Dithering
attempts to reproduce various shades of gray (or all col-
ors) from only a few different 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
fraction of dots to represent each distinct level. Dif-
ferent dither algorithms 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 technol-
ogy developed by Raph Levien. It offers superior smooth-
ness in highlights and midtones, and increased accuracy in
shadows, resulting in significantly improved results over-
all. 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 informa-
tion.
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 printing
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 print-
ers, 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 algorithm) perform very well at high densities, and are
capable of rendering very fine detail well, but they tend
to exhibit artifacts in the form of "waves" or "worms" of
dots which results in noticeable texturing 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 recom-
mended.
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@whin-
latter.uklinux.net)
SEE ALSOgimpprint-color(7), gimpprint-imagetypes(7), gimpprint-
inktypes(7), gimpprint-mediasizes(7), gimpprint-media-
sources(7), gimpprint-mediatypes(7), gimpprint-models(7),
gimpprint-resolutions(7).
Version 4.2.5 24 Jan 2003 GIMPPRINT-DITHERS(7)
