Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1989-06-02
1991-04-16
Britton, Howard W.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358135, H04N 713
Patent
active
050087479
DESCRIPTION:
BRIEF SUMMARY
This application is related to commonly assigned copending application Ser. No. 07/364,441 filed June 2, 1989 naming Messrs. Carr, Perini, O'Donnell and Leaning as inventors and claiming priority dates of Aug. 28 1987 and Oct. 19, 1987 via PCT/GB88/00709 filed Aug. 26 1988.
The present invention relates to coding of video signals, especially using conditional replenishment coding, where information is generally transmitted only in respect of elements of a frame of the picture which have changed relative to a previous frame; the transmitted data being used at a receiver to update a stored version of the picture.
Thus picture elements of each block of an image to be coded are compared with those of the corresponding block of a previously coded image to determine whether the block has changed between the two images; if so, picture element data are generated for output.
Such a system is described in international patent application published under no. WO86/03922, which also proposes that the block be compared with the corresponding block of an earlier (reference) image. If they are deemed to be the same, no picture data are generated--instead, a codeword is produced to indicate that the receiver is to obtain its data from a locally stored replica of the reference image.
According to one aspect of the present invention, there is provided a method of coding an image comprising, for each of a plurality of blocks of an image: block of a previously coded image to produce a matrix of values each indicating whether the corresponding element is, in accordance with a predetermined criterion, deemed to have changed between the two images; each of which identifies a region of the block as being deemed to have changed, and generating a codeword identifying that one matrix of the set; corresponding block of a reference image composed of blocks from at least one earlier frame to determine whether the block is, in accordance with a predetermined criterion, deemed to have changed between the two images; all the elements within the region are identified by comparison step (iii) as being unchanged relative to the reference image, whereupon a codeword indicating this is generated.
In another aspect, the invention provides an apparatus for coding an image comprising, picture elements of the block with those of the corresponding block of a previously coded image to produce a matrix of values each indicating whether the corresponding element is, in accordance with a predetermined criterion, deemed to have changed between the two images; matrices each of which identifies a region of the block as being deemed to have changed, and generate a codeword identifying that one matrix of the set; at least one earlier frame and means for comparing picture elements of the block with those of the corresponding block of the reference image to determine whether the block is, in accordance with a predetermined criterion, deemed to have changed between the two images; region, unless all the elements within the region are identified by the means for comparing as being unchanged relative to the reference image, whereupon a codeword indicating this is generated.
The matching step--often termed vector quantisation--of two-dimensional maps has been proposed previously for picture coding, for example in European patent application Ser. No. 0239076A, where blocks of transform coefficient blocks are classified.
The present invention, however, further exploits the vector quantisation, in that not only can the classification be used (if desired) to reduce the amount of information that has to be transmitted to indicate which elements have been coded for output, but also the number of occasions on which a "reference" codeword is instead generated are increased.
Some embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a block diagram of a coder according to one embodiment of the invention;
FIG. 2 shows a typical bit map produced by the change detector of the coder of FIG. 1;
FI
REFERENCES:
patent: 4369464 (1983-01-01), Temime
patent: 4542411 (1985-09-01), Imanaka et al.
patent: 4591909 (1986-05-01), Kuroda
patent: 4667233 (1987-05-01), Furukawa
patent: 4717957 (1988-01-01), Santamaki
patent: 4734767 (1988-03-01), Kaneko
Carr Michael D.
Leaning Anthony R.
British Telecommunications public limited company
Britton Howard W.
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