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EP0215229A2 Expired / Lapsed EP ⏱️ 0.0 years remaining

Method for compressing bi-level data

Assignee: International Business Machines Corp
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Filing: 1986-07-15
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Granted: —
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Expires: 2006-07-15
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Abstract

Abstract A method for arithmetically compressing bi-level data of an image samples history pels which are adjacent pels to a current pel to be processed and pels so separated from the adjacent pels as to adapt to a period of a dither matrix for a dither image. The sampled pels are deter­mined as to which of dither dominant image pattern or text-graphic dominant image pattern an image of the sampl­ed pels has, to generate the first signal representing that the image has the dither dominant image pattern, the second signal representing that the image has the text-­graphic dominant image pattern or the third signal re­presenting that the image is not classified as the both image patterns. The first, second and third signals are applied to an up-down counter which accumulates the occurrences of the signals to produce, when the accumu­lated value exceeds an upper threshold or a lower threshold, a control signal for selectively swiching access to the first and second statistic tables, which store, at each entry, the most probable symbol and the probability of less probable symbol for the image of the text-graphic image and the dither image, respectively.

Inventors

  • 👤 Business Machine International

Bibliographic Details

Application Number —
Jurisdiction EP
Data Source google_patents
Last Synchronized 2026-10-30 10:39
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/40; H04N1/40062; H04N1/41; H04N1/4105

Claims Analysis

Total Claims: 5
Claim 1
Independent Claim 204 words
A method for compressing a bi-level data stream, each data representing one pel of text/graphic image or dither image comprising steps of: sampling previously processed, adjacent pels to a current pel to be processed and pels so separated from said adjacent pels as to adapt to a period of a dither matrix for said dither image, determining bi-level data of said adjacent pels and said separated pels for identifying image represented by said adjacent pels and said separated pels as said text/graphic image or said dither image, selectively accessing one of first and second statistic table in accordance with said determi­nation by using said bi-level data of said adjacent pels and said separated pels as an address for said selected table, said first table at each entry storing most probable symbol and probability of less probable symbol for said bi-level data of said adjacent pels and said separated pels of said dither image, comparing bi-level data of said current pel with said most probable symbol in said addressed entry, producing coded data in accordance with said com­parison and said probability of less probable symbol in said addressed entry, modifying said most probable symbol and said proba­bility of less probable symbol in said addressed entry.
Claim 2
Independent Claim 204 words
A method for compressing a bi-level data stream, each data representing one pel of text/graphic image or dither image comprising steps of: sampling previously processed, adjacent pels to a current pel to be processed and pels so separated from said adjacent pels as to adapt to a period of a dither matrix for said dither image, determining bi-level data of said adjacent pels and said separated pels for identifying image represented by said adjacent pels and said separated pels as said text/graphic image or said dither image, selectively accessing one of first and second statistic table in accordance with said determi­nation by using said bi-level data of said adjacent pels and said separated pels as an address for said selected table, said first table at each entry storing most probable symbol and probability of less probable symbol for said bi-level data of said adjacent pels and said separated pels of said dither image, comparing bi-level data of said current pel with said most probable symbol in said addressed entry, producing coded data in accordance with said com­parison and said probability of less probable symbol in said addressed entry, modifying said most probable symbol and said proba­bility of less probable symbol in said addressed entry.
Claim 3
Dependent Claim 31 words
A method for compressing bi-level data stream as set forth in Claim 1, wherein said adjacent pels and said separated pels are distributed in a previous line and a current line.
Claim 4
Independent Claim 86 words
A method for compressing a bi-level data stream as set forth in Claims 1 or 2, wherein said image represented by said bi-level data of said adjacent pels and said separated pels is determined as to which of dither dominant image pattern or text/­graphic dominant image pattern said image has, in order to generate the first or second signal, said first signal representing that said image has said dither dominant image pattern, and said second signal representing that said image has said text/­graphic dominant image pattern.
Claim 5
Independent Claim 66 words
A method for compressing a bi-level data stream as set forth in Claims 1 to 3, wherein said first and second signals are accumulated in an updown counter which generates a first decision-signal when accu­mulated occurrences reach one threshold and a second decision-signal when said accumulated occurrences reach another threshold, and said decision-signals are used to selectively access one of said first and second statistic tables.

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