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  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 ALSO
       gimpprint-color(7),     gimpprint-imagetypes(7),     gimp-
       print-inktypes(7),     gimpprint-mediasizes(7),      gimp-
       print-mediasources(7),    gimpprint-mediatypes(7),   gimp-
       print-models(7), gimpprint-resolutions(7).



Version 4.2.6              11 Jan 2004       GIMPPRINT-DITHERS(7)