Facsimile and static presentation processing – Facsimile – Recording apparatus
Patent
1985-04-12
1987-03-31
Capossela, Ronald C.
Facsimile and static presentation processing
Facsimile
Recording apparatus
358 75, 358 78, 358 80, 358284, H04N 140
Patent
active
046547215
ABSTRACT:
A system for producing improved halftone images from continuous tone input images, the pixels of which have been digitized as gray scale values, using a printer having the capability to print a set of output pel patterns producing a respective set of discrete gray scale values, is disclosed. Blocks of pel patterns with discrete gray scale values approximating the gray scale values of the input pixels are selected for printing, and the error in a first block due to the difference between the gray scale value associated with the block and the gray scale value of the corresponding input pixel, is determined. To diffuse this error it is distributed to at least two adjacent blocks using a random number generator to determine the distribution such that a random fraction of said error is distributed to one block and the remainder is distributed to the other block. This error diffusion process is carried through the adjacent blocks taking into account the error fraction already assigned. For edge enhancement the brightness gradient surrounding each input pixel is determined and a threshold value is set below which said gradient is classified as small and above which it is classified as large. When said gradient is small, the selected discrete pattern is printed for the pixel, and when said gradient is large, the pel pattern is altered and the block representing the pixel is printed biasing the pels therein toward the darker input pixels.
REFERENCES:
patent: 4315280 (1982-02-01), Tsuda
patent: 4430668 (1984-02-01), Miles, Jr.
patent: 4463374 (1984-07-01), Thompson
patent: 4464677 (1984-08-01), Kuhn et al.
patent: 4485408 (1984-11-01), Kamizyo et al.
patent: 4495522 (1985-01-01), Matsunawa et al.
Goertzel Gerald
Thompson Gerhard R.
Capossela Ronald C.
Dowd Thomas P.
International Business Machines - Corporation
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