Image analysis – Image compression or coding – Quantization
Patent
1997-10-15
2000-02-15
Lee, Thomas D.
Image analysis
Image compression or coding
Quantization
382237, 358456, G06K 936, G06K 938, G06K 946
Patent
active
060261994
ABSTRACT:
The invention relates to the halftoning of grey values of pixels obtained by a photoelectric scanning of an image. The grey values of the pixels for processing are thresholded, the quantisation error which occurs in these circumstances being added to the grey value of an adjacent yet to be thresholded and situated in a first or second direction of the image. The selection of a pixel in the first or second direction is determined in these conditions by the differences in grey values of not more than two pixels arranged in both directions and situated in the vicinity of the thresholded pixel. The pixel is preferably selected in the direction in which the smallest difference in grey value is encountered, i.e. not in the direction of the grey value gradient but exactly perpendicularly to it. It has been found that the edge transitions can be reproduced most sharply in this way.
REFERENCES:
patent: 4876610 (1989-10-01), Ohsawa et al.
patent: 4878125 (1989-10-01), Katayama et al.
patent: 5140432 (1992-08-01), Chan
patent: 5363210 (1994-11-01), Sasaki et al.
patent: 5515456 (1996-05-01), Ballard
"Digital Halftoning" by Robert Ulichney, Chapter 8 of MIT Press, 1987, p. 238-279.
Fox et al., "Multiple Error correction Algorithm for Halfton, Continuous Tone and Text Reproduction," IBM Technical Disclosure Bulletin, vol. 23, No. 10 (Mar. 1981) pp. 4433-4435.
Eschbach et al., "Analytic Description of the 1-D Error Diffusion Technique for Halftoning," Optics Communications, vol. 52, No. 3 (Dec. 1, 1984) pp. 165-168.
Lee Thomas D.
Oce--Technologies B.V.
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