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
358105, 358135, H04N 713
Patent
active
050087487
DESCRIPTION:
BRIEF SUMMARY
This application is related to copending commonly assigned application Ser. No. 07/364,442 filed June 2, 1989 to Messrs. Carr and Leaning and claiming priority of Oct. 10, 1987 via PCT/GB No. 88/00871 filed Oct. 10, 1988.
The present invention relates to signal coding, and particularly, though not exclusively, to coding of video signals, especially using conditional replenishment coding, where information is transmitted only in respect of elements of a frame of the picture which have changed relative to the previous frame; the transmitted data being used at a receiver to update a stored version of the picture.
According to one aspect of the present invention there is provided a method of coding a set of values comprising selecting that one of a plurality of possible sequences of the values which has the highest correlation between successive values in the sequence, and supplying representations of those values to an output; wherein some of the representations are the differences between the relevant value and a prediction based on at least the immediately preceding value in the selected sequence.
Although the method is applicable to other forms of signal, it finds particular application in video coding. Thus in another aspect we provide a method of coding an image comprising, for the image area or for each of a plurality of individual areas thereof, selecting that one of a plurality of possible sequences of the picture elements within the area which has the highest correlation between successive elements in the sequence, and supplying representations of those elements to an output; wherein some of the representations are the differences between values of the relevant element and a prediction based on the value of at least the immediately preceding element in the selected sequence.
Normally the representations will be transmitted in an order which corresponds to the selected sequence, though this is not in principle essential.
The choice of squence may be made by evaluating different sequences, but in some circumstances it may be possible to infer an appropriate choice from earlier coding steps. Thus in a further aspect of the 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; least some of the elements being coded as the difference between that element and a predicted value for that element derived from one or more previously coded elements of the block, the sequence of coding of the elements being dependent on the orientation of the identified region.
The invention also extends to coding apparatus for performing the method.
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 one possible form of coder according to the invention;
FIG. 2 illustrates a movement matrix;
FIGS. 3a-3h illustrate some vector quantisation (VQ) shapes;
FIG. 4, 5 and 6 illustrate possible scan paths; and
FIG. 7 is a block diagram of a change of movement detector which may be used in the apparatus of FIG. 1.
FIG. 1 shows a conditional replenishment video coder, where video signals (assumed to be in digital form) are supplied to an input 1. The current frame of a picture is compared in a change or movement detector 2 with the output of a local decoder 3. The local decoder produces a "previous frame" output which is the same as that produced by a remote decoder; the object of the comparison is to identify those parts of the picture which have changed so that only information concerning those parts needs to be sent to the decoders, to update a stored representation of the frame.
The signals are processed on a block-by-block basis--an 8.times.8 block is assumed--and the change detect
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patent: 4827338 (1989-05-01), Gerard
Carr Michael D.
Leaning Anthony B.
Leaning Anthony R.
O'Donnell John
Perini Maurice G.
British Telecommunications public limited company
Britton Howard W.
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