gimpprint-dithers.7.in   [plain text]


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.\" Copyright (C) 2000 Roger Leigh <roger@whinlatter.uklinux.net>
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.TH GIMPPRINT-DITHERS 7 "@RELEASE_DATE@" "Version @GIMPPRINT_VERSION@" "Gimp-Print Manual Pages"
.SH NAME
gimpprint-dithers \- Gimp-Print dither algorithms
.SH DESCRIPTION
Gimp-Print includes several dither algorithms.  Dithering attempts to reproduce
various shades of gray (or all colors) 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.
Different dither algorithms are suited to different purposes, and some are
significantly faster than others.
.SH DITHER ALGORITHMS
.TS
li li
lb l.
Dither Algorithm	Description
_
Adaptive	Adaptive Hybrid
EvenTone	EvenTone screening (experimental)  
Ordered	Ordered 
Fast	Fast
VeryFast	Very Fast
Floyd	Hybrid Floyd-Steinberg
.TE
.PP
For the highest quality, we recommend use of \fIAdaptive Hybrid\fP dithering.
For continuous tone images, \fIOrdered\fP works just as well and is somewhat
faster.  Ordered dithering yields noticeably inferior results with text and
intricate line art, particularly at high resolutions.
.PP
\fIEvenTone\fP dithering is a relatively new screening technology developed by
Raph Levien.  It offers superior smoothness in highlights and midtones, 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.
.PP
\fIFast\fP 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 printers, the results should
be very similar to Ordered.
.PP
\fIVery Fast\fP 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.
.PP
\fIError diffusion\fP algorithms (\fIHybrid Floyd-Steinberg\fP 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 recommended.
.SH COPYRIGHT
Copyright \(co 2001 Michael Sweet (mike@easysw.com) and Robert Krawitz
(rlk@alum.mit.edu)
.PP
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.
.PP
This manual page was written by Roger Leigh (roger@whinlatter.uklinux.net)
.SH SEE ALSO
.BR gimpprint-color (7),
.BR gimpprint-imagetypes (7),
.BR gimpprint-inktypes (7),
.BR gimpprint-mediasizes (7),
.BR gimpprint-mediasources (7),
.BR gimpprint-mediatypes (7),
.BR gimpprint-models (7),
.BR gimpprint-resolutions (7).
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