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EP0066697A1
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A method and system for compressing grey scale image data
Assignee: International Business Machines Corp
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Filing: 1982-04-21
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Granted: —
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Expires: 2002-04-21
Abstract
Abstract The present invention relates to a method and system for compacting grey-scale image data. The system permits the use of a «zero bit» per pel mode for the data transmission (1 «error bit» per pel actually transmitted) and provides for the automatic detection of the particular variable length compression code utilized for transmitting the quantized error (Ey) for a particular pel. Utilizing the concepts of the present invention compression rates of approximately 1.5 bits have been obtained. The system comprises, first prediction means (28) for predicting the grey scale value of a current pel which is to be transmitted, utilizing the values of previously transmitted pels, second prediction means (26) for predicting the code which should suffice for transmitting the quantized error for correcting the predicted pel grey scale value to approximately the true value of said pel, means for determining the code which is actually needed to encode the quantized error, means (30) for producing a first special purpose code bit when the predicted range of codes for encoding the quantized error is sufficient and a different bit when it is insufficient, and means (30) for generating a first quantized error code when the predicted range of codes is sufficient and a second code when it is insufficient.
Inventors
- 👤 Dimitris Anastassiou
- 👤 Joan Laverne Mitchell
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-05 12:16
CPC Classifications
H; H03; H03M; H03M7/00; H03M7/30; H03M7/40; H03M7/4006; H04; H04N; H04N19/00; H04N19/10; H04N19/102; H04N19/124; H04N19/50; H04N19/13; H04N19/60; H04N19/90; H04N19/91
Claims Analysis
Total Claims: 21
Claim 1
Independent Claim
135 words
A method for compressing grey scale image data characterised in that the method comprises the steps of predicting (28) the grey scale value of a current pel which is to be processed, utilizing the grey scale values of previously processed pels, predicting (26) the number of bits which should suffice for encoding the quantized error for correcting the predicted grey scale pel value to approximately the true value of the current pel, determining the minimum number of bits which are actually needed to encode the quantized error, producing (30) a first, special purpose code bit when the predicted number of bits for encoding the quantized error is sufficient and a different bit when it is insufficient, and generating (30) a code word for indicating the required quantization value for modification of the predicted pel value.
Claim 2
Independent Claim
135 words
A method for compressing grey scale image data characterised in that the method comprises the steps of predicting (28) the grey scale value of a current pel which is to be processed, utilizing the grey scale values of previously processed pels, predicting (26) the number of bits which should suffice for encoding the quantized error for correcting the predicted grey scale pel value to approximately the true value of the current pel, determining the minimum number of bits which are actually needed to encode the quantized error, producing (30) a first, special purpose code bit when the predicted number of bits for encoding the quantized error is sufficient and a different bit when it is insufficient, and generating (30) a code word for indicating the required quantization value for modification of the predicted pel value.
Claim 3
Dependent Claim
42 words
A method as claimed in Claim 1, including determining that no quantization of the predicted grey scale value is necessary and producing said first special purpose code bit in response thereto and producing no quantized error code indication of a quantization correction.
Claim 4
Dependent Claim
26 words
A method as claimed in Claim 2, including further compacting the resultant code stream by arithmetically encoding said special purpose bits and the quantized error bits.
Claim 5
Dependent Claim
31 words
A method as claimed in Claim 3, including arithmetically coding the special purpose bits using a first probability model and arithmetically coding any quantized error bits using a second probability model.
Claim 6
Dependent Claim
44 words
A method as claimed in Claim 4, including coding said special purpose bits utilizing an adaptive probability determination involving determining the MODE related to the particular special purpose bit and the total image history up to that point where the same MODE was used.
Claim 7
Dependent Claim
141 words
A data compression system for compressing grey scale image data characterised in that the system comprises first prediction means (28) for predicting the grey scale value of a current pel which is to be processed, utilizing the values of previously processed pels, second prediction means (26) for predicting the code which should suffice for transmitting the quantized error for correcting the predicted pel grey scale value to approximately the true value of the current pel, means for determining the code which is actually needed to encode the quantized error, means (30) for producing a first special purpose code bit when the predicted range of codes for encoding the quantized error is sufficient and a different bit when it is insufficient, and means (30) for generating a code word for indicating the required quantization value for modification of the predicted pel value.
Claim 8
Dependent Claim
141 words
A data compression system for compressing grey scale image data characterised in that the system comprises first prediction means (28) for predicting the grey scale value of a current pel which is to be processed, utilizing the values of previously processed pels, second prediction means (26) for predicting the code which should suffice for transmitting the quantized error for correcting the predicted pel grey scale value to approximately the true value of the current pel, means for determining the code which is actually needed to encode the quantized error, means (30) for producing a first special purpose code bit when the predicted range of codes for encoding the quantized error is sufficient and a different bit when it is insufficient, and means (30) for generating a code word for indicating the required quantization value for modification of the predicted pel value.
Claim 9
Dependent Claim
51 words
A system as claimed in Claim 6, wherein said second prediction means includes means for determining what quantized error is necessary to map to the required quantization value of a predetermined quantization characteristic in order to generate the best possible coded approximation of the grey scale value of the current pel.
Claim 10
Dependent Claim
41 words
A system as claimed in Claim 6 or 7, wherein said means for predicting the grey scale value of the pel including means for storing the generated grey scale values for a plurality of predetermined history pels produced by the system.
Claim 11
Dependent Claim
40 words
A system as claimed in Claim 8, wherein said means for predicting the code which should suffice for generating the quantized error includes means for storing the quantized error which was actually generated for said plurality of pre-determined history pels.
Claim 12
Dependent Claim
47 words
A system as claimed in Claim 9, wherein said means further includes microprocessor means for selecting the largest of the quantized error signals of said history pels and an indication of the range of codes which should suffice for encoding the quantized error for the current pel.
Claim 13
Dependent Claim
94 words
A system as claimed in Claim 1, in combination with a system for decompressing data comprising means for decompressing said compressed code comprising a first and second prediction means substantially identical to those in said compression means, means responsive to the output of said first and second prediction means for decoding the quantized error from the compressed message stream, means for producing other required quantization value from the decoded quantized error and, means for generating the decompressed grey scale value Y from the output of said first prediction means and the derived quantization value.
Claim 14
Dependent Claim
38 words
A system as claimed in Claim 11, said means for predicting the grey scale value of the pel including means for storing the generated grey scale values for a plurality of predetermined history pels produced by the system.
Claim 15
Dependent Claim
42 words
A system as claimed in Claim 12, wherein said second prediction means for predicting the code which should suffice for generating the quantized error includes means for storing the quantized error which was actually generated for said plurality of pre-determined history pels.
Claim 16
Dependent Claim
82 words
A system as claimed in Claim 13, wherein said second prediction means includes means for predicting the number of code bits for generating the proper quantized error code for the current pel, means for determining the actual number of bits necessary to generate the proper quantized error code and, means for predicting said first special purpose bit when the predicted number of bits is adequate to encode the proper quantized error whereby a continuously adaptable fixed length quantized error code is produced.
Claim 17
Dependent Claim
32 words
A system as claimed in Claim 14, wherein said means for operating said second quantized error code includes means for generating a variable length compression code representative of the required quantized error.
Claim 18
Dependent Claim
52 words
A system as claimed in Claim 15, wherein said second prediction means further includes microprocessor means for selecting the largest of the quantized error signals of said history pels and for determining as a function thereof the number of bits which should suffice for encoding the quantized error for the current pel.
Claim 19
Dependent Claim
28 words
A system as claimed in Claim 16, including means for arithmetically coding and decoding the resultant message comprising the special purpose bits, and bits coding the quantized error.
Claim 20
Dependent Claim
39 words
A system as claimed in Claim 17, wherein said arithmetic coding and decoding means utilizes a first probability model for coding and decoding the special purpose bits and a second model for coding and decoding the quantized error bits.
Claim 21
Dependent Claim
39 words
A system as claimed in Claim 18, wherein said means for arithmetic coding and decoding includes means for maintaining for a particular image, the MODE history statistics for each MODE and for determining the MODE for a current pel.
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