|EvenTone||EvenTone screening (experimental) |
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 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.
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 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.
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 (email@example.com)