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 4.2.5                     24 Jan 2003             GIMPPRINT-DITHERS(7)