公开(公告)号：CA2122170A1

公开(公告)日：1995-01-09

申请号：CA2122170

申请日：1994-04-26

Applicant: IBM

Inventor： HASSNER MARTIN A ,  KARNIN EHUD D ,  SCHWIEGELSHOHN UWE ,  TAMURA TETSUYA

IPC: G06F5/00 ,  G06T9/00 ,  H03M7/30 ,  H04B1/66

Abstract: COMBINATION PARALLEL/SERIAL EXECUTION OF SEQUENTIAL ALGORITHM FOR DATA COMPRESSION/DECOMPRESSION An apparatus and method for executing a sequential data compression algorithm that is especially suitable for use where data compression is required in a device (as distinguished from host) controller. A history buffer compresses an array of i identical horizontal slice units. Each slice unit stores j symbols to define j separate blocks in which the symbols in each slice unit are separated by exactly i symbols. Symbols in a string of i incoming symbols are compared by i comparators in parallel with symbols previously stored in the slice units to identify matching sequences of symbols. A control unit controls execution of the sequential algorithm to condition the comparators to scan symbols in parallel but in each of the blocks sequentially and cause matching sequences and nonmatching sequences of symbols to be stored in the array. The parameters i and j are selected to limit the number of comparators required to achieve a desired degree of efficiency in executing the algorithm based upon a trade-off of algorithm execution speed versus hardware cost. A priority encoder calculates from signals output by the slice units each j,i address in which a matching sequence is identified, but it outputs the address of only one (such as the smallest) of these addresses.

公开(公告)号：CA2019133C

公开(公告)日：1995-05-30

申请号：CA2019133

申请日：1990-06-15

Applicant: IBM

Inventor： CHEVION DAN S ,  KARNIN EHUD D ,  WALACH EUGENIUSZ

IPC: G06T9/00 ,  H04N1/411 ,  H04N1/413

Abstract: 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 the following 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; and (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).

公开(公告)号：CA2019134A1

公开(公告)日：1991-02-04

申请号：CA2019134

申请日：1990-06-15

Applicant: IBM

Inventor： CHEVION DAN S ,  KARNIN EHUD D ,  WALACH EUGENIUSZ

IPC: G06T9/00 ,  H04N1/411