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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 system. United States Patent 1790723, issued 3 February 1931.〕 Ranger's invention permitted continuous tone photographs to be converted first into black and white, then transmitted to remote locations, which had a pen moving over a piece of paper. To render black, the pen was lowered to the paper; to produce white, the pen was raised. Shades of gray were rendered by intermittently raising and lowering the pen, depending upon the luminance of the gray desired. Ranger's invention used capacitors to store charges, and vacuum tube comparators to determine when the present luminance, plus any accumulated error, was above a threshold (causing the pen to be raised) or below (causing the pen to be lowered). In this sense, it was an analog version of error diffusion. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Error diffusion」の詳細全文を読む スポンサード リンク
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