EP0339589A2
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EP
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Orthogonal transform coding system for image data
Assignee: Sharp Corp
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Filing: 1989-04-25
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Granted: —
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Expires: 2009-04-25
Abstract
Abstract An orthogonal transform coding system for images which orthogonally transforms image data to spatial frequencies and divides the domain of the spatial frequencies into low and high frequency domains using a plurality of domain patterns prepared in advance. This system quantizes and encodes the high and low frequency domains of the orthogonally transformed data by different methods. Coding of the data in the low frequency domain is performed based on bits which are allocated to those data in accordance with their energies. The data in the high frequency domain are decomposed into bit planes and run-length coding is performed for each bit plane, whereby a small number of bits are allocated to those data in the low frequency domain in the coding and an efficient coding of images is accomplished.
Inventors
- 👤 Tomoko Aono
- 👤 Masao Izumi
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-29 10:08
CPC Classifications
H; H04; H04N; H04N19/00; H04N19/90; H04N19/94; H04N19/10; H04N19/134; H04N19/136; H04N19/14; H04N19/169; H04N19/184; H04N19/30; H04N19/37; H04N19/60
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
256 words
An orthogonal transform coding system for image data, which comprises steps of: orthogonally transforming image data from space coordinates to spatial frequencies; preparing a plurality of domain patterns each of which has low and high frequency domains therein and is used for dividing a spatial frequency domain of orthogonally transformed image data into a low frequency domain and a high frequency domain according to a threshold; summing absolute values of the orthogonally transformed data belonging to the low frequency domain of each of said domain patterns; specifying the low frequency domain of a domain pattern in which the sum of the absolute values is the largest as a low frequency domain of the orthogonally transformed image data and specifying the high frequency domain of the same domain pattern as a high frequency domain of the orthogonally transformed image data; encoding the orthogonally transformed data in the low frequency domain by dividing the low frequency domain into a plurality of blocks and calculating respective mean values of the orthogonally transformed data in the blocks so as to allocate a large number of bits to a block which has a mean value larger than a specified value and a small number of bits to a block which has a mean value smaller than the specified value; and encoding the orthogonally transformed data in the high frequency domain in a manner different from that for encoding the orthogonally transformed data in the low frequency domain so as to allocate a small number of bits to the high frequency domain.
Claim 2
Dependent Claim
256 words
An orthogonal transform coding system for image data, which comprises steps of: orthogonally transforming image data from space coordinates to spatial frequencies; preparing a plurality of domain patterns each of which has low and high frequency domains therein and is used for dividing a spatial frequency domain of orthogonally transformed image data into a low frequency domain and a high frequency domain according to a threshold; summing absolute values of the orthogonally transformed data belonging to the low frequency domain of each of said domain patterns; specifying the low frequency domain of a domain pattern in which the sum of the absolute values is the largest as a low frequency domain of the orthogonally transformed image data and specifying the high frequency domain of the same domain pattern as a high frequency domain of the orthogonally transformed image data; encoding the orthogonally transformed data in the low frequency domain by dividing the low frequency domain into a plurality of blocks and calculating respective mean values of the orthogonally transformed data in the blocks so as to allocate a large number of bits to a block which has a mean value larger than a specified value and a small number of bits to a block which has a mean value smaller than the specified value; and encoding the orthogonally transformed data in the high frequency domain in a manner different from that for encoding the orthogonally transformed data in the low frequency domain so as to allocate a small number of bits to the high frequency domain.
Claim 3
Dependent Claim
42 words
The orthogonal transform coding system as claimed in Claim 1, wherein the step of encoding the orthogonally transformed data in the high frequency domain includes steps of decomposing these data into bit planes and performing run length coding for each bit plane.
Claim 4
Dependent Claim
112 words
The orthogonal transform coding system as claimed in Claim 1, wherein the step of encoding the orthogonally transformed data in the high frequency domain includes steps of dividing the high frequency domain into a plurality of blocks and comparing data patterns of the orthogonally transformed data in the respective blocks with a limited number of representative data patterns that are stored in a memory so as to select representative patterns which are the closest to the respective data patterns of the orthogonally transformed image data with respect to each of the blocks so as to encode the high frequency domain of the orthogonally transformed data according to indexes representing selected representative patterns.
Claim 5
Dependent Claim
21 words
The orthogonal transform coding system as claimed in Claim 1, wherein a discrete cosine transform is used as an orthogonal transform.
References Cited (Backward Citations)
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