Dither Filters

This is version 1.8 of my Photoshop Dither Filter package, a collection of two filters for Adobe Photoshop that dither color or grayscale images to black and white so that they can be printed on a bilevel device, such as a laser printer. When printing to a laser printer, the dithering algorithms in these filters may be superior to the halftoning algorithms that are built into Photoshop. Why is that? Laser printers suffer from a problem called dot gain: isolated black pixels on the printed page are larger than they "should" be. In fact, a certain amount of dot gain is unavoidable: since the dots that a laser printer makes are round, each dot has to overlap slightly with its neighbors so that the laser printer can produce a solid black. What this means is that most laser printer output is slightly darker than it should be. In practice, most laser printers produce dots which are somewhat larger than this minimum necessary dot size, making the problem even worse. The two filters in the Photoshop Dither Filter package compensate for dot gain when they halftone an image. For more information see the enclosed README file or the web page, http://pertsserver.cs.uiuc.edu/~hull/halftone/ This version fixes a bug in VGDither, and adds some minor new features. The files in this archive were checked for viruses with Disinfectant 3.6. The file belongs in gst/grf/pshp/dither-filter-18.hqx and replaces dither-filter-16.hqx which is already there. The package is freeware.