EP0411232B1
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Method for high-quality compression by binary text images
Assignee: International Business Machines Corp
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Filing: 1989-10-10
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Granted: 1995-12-27
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Expires: 2009-10-10
Abstract
No abstract record available.
Inventors
- 👤 Dan Shmuel Dr. Chevion
- 👤 Ehud Dov Dr. Karnin
- 👤 Eugeniusz Dr. Walach
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 11:22
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/41; H04N1/411; G; G06; G06T; G06T9/00
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
121 words
Method for high-quality compression of binary text images for storage and possible future processing including transmission over data links, involving the scanning thereof on the record carrier on which they are presented in a pixel-by-pixel raster scan and deriving a string of digital data from the scanner output, and partitioning said image into segments, characterized by the steps of determining the degree of compressibility of a segment by taking into consideration the number of uninterruped runs of '1' or '0' within said segment and assigning according to said degree of compressibility one of at least two different compression ratios, one of which being lossy, to the data of said segment and compressing said data in accordance with said one compression ratio.
Claim 2
Dependent Claim
37 words
Method in accordance with claim 1, characterized in that the average length of said number of uninterrupted runs of "1" or "0" in one segment is determined to determine the degree of compressibility of said one segment.
Claim 3
Dependent Claim
137 words
Method in accordance with any of claim 1 or 2, characterized in that at the start of each segment, two registers for storing a first and a second number (m, n) are cleared, that all lengths (w) of uninterrupted runs of "0" or "1" are determined, that if a length (w) is larger than a predetermined length value (w t ), it is ignored. otherwise, the first number (n) is incremented by 1, and the second number (m) by w, and that at the end of the segment the feasibility of compression is determined by checking whether n is lower than a predetermined first threshold (n t ), or whether the ratio m/n exceeds a predetermined second threshold ([m/n] t ), in which cases lossy compression is performed while in all other cases lossless compression is performed.
Claim 4
Dependent Claim
38 words
Method in accordance with claim 3, characterized in that the said predetermined length value (w t ) is 12, that said first threshold (n t ) is 5, and that said second threshold ([m/n] t ) is 4.
Claim 5
Dependent Claim
123 words
Method in accordance with any of claim 1 or 2, characterized in that for each segment the number (m) of nonzero bytes containing at least one "1" respectively is counted and each such byte is translated into a binary number which - equals 1 if the byte under consideration contains a small black or white interval, that is, that byte does not equal either 00000000 or 11111111 and the first bit of the byte equals the last one, and which - equals 0 in all other cases, that the number (n) of pairs of consecutive "1"-s is counted, and that lossy compression is performed if n is smaller than a predetermined threshold and/or if n is smaller than a predetermined fraction of m.
Claim 6
Dependent Claim
19 words
Method in accordance with claim 5, characterized in that the threshold is 3, and that fraction equals 5 %.
Claim 7
Dependent Claim
74 words
Method in accordance with any the preceding claims, characterized in that said step of determining the degree of compressibility of the individual features of the original image is preceded by a prefiltering step involving the filtering of the scan data prior to compression through forced changing of all isolated "1" pixels as well as all horizontal and vertical sequences of "1" pixels to "0" if the said sequences are shorter than a predetermined length.
Claim 8
Dependent Claim
18 words
Method in accordance with claim 7, characterized in that the said predetermined length is set to three pixels.
Claim 9
Dependent Claim
29 words
Method in accordance with any of the preceding claims, characterized in that the segments are defined by partitioning the entire image area into mutually exclusive segments of uniform size.
Claim 10
Dependent Claim
31 words
Method in accordance with claim 9, characterized in that the mutually exclusive segments each correspond to a line or to two consecutive lines of scan of the original binary text image.
Claim 11
Dependent Claim
90 words
Method in accordance with any of the preceding claims, characterized in that the lossy compression involves steps of defining 2 × 2 blocks of pixels, and developing for each such block a i-bit representation by assigning a "0"-value to all blocks having less than two black pixels, and a "1"-value to all blocks having more than two black pixels, and by assigning a "0"-value to all blocks having exactly two black pixels, provided such an assignment does not break a connection between two lines and does not distort line curvature.
References Cited (Backward Citations)
No citation records indexed.
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