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 fraction of dots to represent each distinct level.  Different 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 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 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.

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@whinlatter.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)