Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1986-10-01
1988-12-13
Britton, Howard W.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358133, H04N 712
Patent
active
047914866
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns methods and apparatus for image coding and transmission.
The proposals are suitable for the coding of both still pictures and moving pictures, and are particularly, though not exclusively, aimed at low bit rate video coding schemes for applications such as photovideotex and video conferencing.
They aim to reduce some of the drawbacks associated with transform coding whilst achieving a similar or better compression for a given picture quality.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided a method of image transmission comprising repetitively: sample points thereof; criterion, transmitting picture data in respect of the said selected sample points, and if they do not, notionally dividing the are under consideration into two or more sub-areas and subjecting each sub-area to steps (a), (b) and (c) until a minimum sub-area size is reached.
A transmitter for such transmission may comprise interpolation means for generating an estimate of a picture area based on a subset of its samples, means for comparing the estimate with the actual sample values, and means arranged in dependence on whether the comparison indicates a difference of more or less than a threshold (a) to select the subset of samples for transmission or (b) to notionally divide the picture area into two or more sub-areas and to process each sub-area in like manner.
The subset of samples may be the four corner points of the area, and the interpolation process may be simple two-dimensional linear interpolation, but this is not essential.
The division into sub-areas may conveniently consist of division into four substantially equal parts.
The data transmitted may comprise a sequence of division codes each indicating whether or not the corresponding area is divided; each division code being followed by the codes corresponding to parts of the respective one. In one preferred arrangement the sample point picture data are transmitted in groups of one or more samples, each group containing data in respect of the untransmitted selected sample(s) of a respective area, the sequence of groups being the same as that of the division codes which indicate that the relevant areas are undivided, whilst in another the sample point picture data are transmitted in groups, each group containing data in respect of those selected samples generated by a respective division, the sequence of groups being the same as that of the division codes which indicate the relevant division.
As indicated the invention may be applied directly to the coding of individual pictures. However, further economy in transmission may be combining it with inter-frame differential coding and applying the present coding method being applied to the difference signal (within the predictor loop).
It will be seen that the principle of the method is a non-uniform sample structure in which non-transmitted pels are interpolated.
It is based on the idea of avoiding the use of irrelevant block structures and frequency-derived transforms whose raisons d'etre are inappropriate mathematical models (Markov processes).
BRIEF DESCRIPTION OF THE DRAWING
One embodiment of the invention will now be described with reference to the accompanying drawings, in which
FIG. 1, 2 and 3 illustrate diagrammatically an image area at various stages of the coding procedure;
FIG. 4 is a flowchart for coder operation;
FIG. 5 is a block diagram of a coder;
FIG. 6 is a flowchart for decoder operation;
FIG. 7 is a block diagram of a decoder;
FIG. 8 illustrates a typical coder sequence; and
FIG. 9 is a block diagram of an inter-frame coder.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
Operation 1
Referring to FIG. 1, a block whose corner points are ABCD is schematically illustrated. The first step in coding is to calculate a new block in which all picture elements (pels) are represented by values linearly interpolated from the corner values at A, B, C and D. This new block is compared with the original and if no differences are found
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Nightingale Charles
Spriggs Hugh
Turkington Roger D.
British Telecommunications public limited company
Britton Howard W.
Kostak Victor R.
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