专利名称：System for reproducing multi-level digital
images on a bi-level printer of fixed dot size
发明人：Gerald Goertzel,Gerhard R. Thompson申请号：US06/722898申请日：19850412公开号：US04654721A公开日：19870331
摘要：A system for producing improved halftone images from continuous tone inputimages, the pixels of which have been digitized as gray scale values, using a printer havingthe capability to print a set of output pel patterns producing a respective set of discretegray scale values, is disclosed. Blocks of pel patterns with discrete gray scale valuesapproximating the gray scale values of the input pixels are selected for printing, and theerror in a first block due to the difference between the gray scale value associated withthe block and the gray scale value of the corresponding input pixel, is determined. Todiffuse this error it is distributed to at least two adjacent blocks using a random numbergenerator to determine the distribution such that a random fraction of said error isdistributed to one block and the remainder is distributed to the other block. This errordiffusion process is carried through the adjacent blocks taking into account the errorfraction already assigned. For edge enhancement the brightness gradient surroundingeach input pixel is determined and a threshold value is set below which said gradient isclassified as small and above which it is classified as large. When said gradient is small, theselected discrete pattern is printed for the pixel, and when said gradient is large, the pelpattern is altered and the block representing the pixel is printed biasing the pels therein
toward the darker input pixels.
申请人：INTERNATIONAL BUSINESS MACHINES CORPORATION
代理人：Thomas P. Dowd
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