METHOD FOR HIGH-QUALITY COMPRESSION OF BINARY TEXT IMAGES

The invention relates to a method for the compression and decompression of binary text 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: 1. Prefiltering to remove all black patches (e.g. by removing all black pixels, except where they belong to a large black segment. 2. Fast Evaluation of Compressibility by partitioning the images into mutually exclusive segments and applying different compression modes to each segment. 3. Connectivity-Oriented Subsampling to reduce the resolution in horizontal and vertical directions. The image is segmented into blocks, and a 1-pixel representation for each block is determined. 4. Lossless Compression and Decompression where the reduced file is compressed by conventional techniques. 5. Reconstruction by sequence reversal. Lossless decompression will retrieve the subsampled file, expansion of the subsampled file through replacement of each pixel by a block having equal value, postfiltering. r