Method for high-quality compression of binary text images

Facsimile and static presentation processing – Facsimile – Reduced time or bandwidth for static image communication

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358462, 358467, H04N 140

Patent

active

052047563

ABSTRACT:
The invention relates to a method for the compression and decompression of binary test images. The method distinguishes between large low-frequency areas and small high-frequency areas in the original frame. For the low-frequency areas, a scheme for lossy compression is used, whereas for the high-frequency areas, a scheme permitting lossless compression is applied. The compression/decompression process involves five stages; namely prefiltering to remove all black patches (e.g. by removing all black pixels, except where they belong to a large black segment), fast evaluation of compressibility by partitioning the images into mutually exclusive segments and applying different compression modes to each segment, connectivity-oriented subsampling to reduce the reslolution in horizontal and vertical directions which cause the image to be segmented into blocks and a 1-pixel representation for each block is determined, lossless compression and decompression where the reduced file is compressed by conventional techniques, and reconstruction by sequence reversal so that lossless decompression will retrieve the subsampled file, expansion of the subsampled file through replacement of each pixel by a block having equal value and postfiltering.

REFERENCES:
patent: 3700797 (1972-10-01), Wernikoff
patent: 4229768 (1980-10-01), Kurahayashi et al.
patent: 4290084 (1981-09-01), Minshull et al.
patent: 4542411 (1985-09-01), Imanaka et al.
IBM Technical Disclosure Bulletin; vol. 20, No. 12 May 1978; "Optical Scanning of Continuous-Tone and Line Documents With Spectial Frequency Separation for Improved Data Handling and Compactor"; pp. 5416-5421.
IBM Tech. Disc. Bull.; vol. 24, No. 9 Feb. 1982; "High Performance Exact Gray-Scale Compression Technique"; pp. 4513-4516.
8th Int. Conf. on Pattern Recog. Proceedings IEEE New York, N.Y., vol. 1, Oct. '86 Paris, France pp. 916-918.

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