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Error Diffusion
Error diffusion is a type of halftoning in which the quantization residual is distributed to neighboring pixels that have not yet been processed. Its main use is to convert a multi-level image into a binary image, though it has other applications. Unlike many other halftoning methods, error diffusion is classified as an area operation, because what the algorithm does at one location influences what happens at other locations. This means buffering is required, and complicates parallel processing. Point operations, such as ordered dither, do not have these complications. Error diffusion has the tendency to enhance edges in an image. This can make text in images more readable than in other halftoning techniques. Early history Richard Howland Ranger received United States patent 1790723 for his invention, "Facsimile system." The patent, which issued in 1931, describes a system for transmitting images over telephone or telegraph lines, or by radio.Richard Howland Ranger, Facsimile ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Halftone
Halftone is the reprographic technique that simulates continuous-tone imagery through the use of dots, varying either in size or in spacing, thus generating a gradient-like effect.Campbell, Alastair. The Designer's Lexicon. ©2000 Chronicle, San Francisco. "Halftone" can also be used to refer specifically to the image that is produced by this process. Where continuous-tone imagery contains an infinite range of colors or greys, the halftone process reduces visual reproductions to an image that is printed with only one color of ink, in dots of differing size ( pulse-width modulation) or spacing (frequency modulation) or both. This reproduction relies on a basic optical illusion: when the halftone dots are small, the human eye interprets the patterned areas as if they were smooth tones. At a microscopic level, developed black-and-white photographic film also consists of only two colors, and not an infinite range of continuous tones. For details, see film grain. Just as color ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
