Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1987-10-05
1989-08-29
Britton, Howard W.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358136, 358105, H04N 713
Patent
active
048622648
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to the coding of video signals and more particularly to the coding of a video signal using adaptive sub-sampling to reduce the bandwidth/bit rate thereof.
The advent of high-definition television (HDTV) signals has led to a considerable amount of research into ways of reducing the bandwidth of such a transmitted HDTV signal without compromising the picture quality thereof unacceptably. In theory, it is possible to realise such a reduction in transmitted bandwidth by optimising the sampling rate according to the varying amounts of picture information present in a picture frame.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method of coding a video signal for transmission in a restricted bandwidth, the method comprising the steps of sub-dividing a frame (or field) of picture information of the video signal into a set of constituent blocks, measuring the amount of picture activity in each block, sampling the picture information in a block at a rate related to the amount of measured activity in that block and adding to each thus coded block a supplementary signal which is related to the sampling rate used in that block.
Thus a decision is made on a block-by-block basis as to whether the block is transmitted to high accuracy or whether it can be adequately reconstructed from the previous frames.
In the method according to the invention, each video component is formed into two parts. The first part consists of the component signal sub-sampled in some manner. The samples occurring at an irregular rate can be written into a buffer store and read out, for transmission, at a regular rate. The samples may be transmitted in an analogue or digital form. The second part consists of a pilot signal to indicate the status of the sub-sampling.
BRIEF DESCRIPTION OF THE DRAWINGS
Specific embodiments of the present 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 for use in the method of the present invention;
FIG. 2 is a schematic diagram of a sub-sampler used in the coder of FIG. 1; and
FIG. 3 is a diagram illustrating the principle of motion-compensated coding in according with the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, a picture is first sampled and split into blocks. For simplicity only the luminance component is shown. For the purposes of explanation the blocks have been limited to cover 4 samples by 4 picture lines, in practice there will be substantially more samples than this. The "activity" of each block is then measured by a method such as one of those described below. For a fixed proportion of the blocks in each frame, i.e., the most active in that frame, all of (or a high percentage of) the samples within these blocks are written into a buffer store before transmission. It is of course equally the case that the present invention could be applied to a video signal on a field-by-field basis instead of frame-by-frame. For the remaining blocks within each picture, only a small percentage (which may be zero) of the samples from each of these blocks are written into the buffer store before transmission. The sub-sampling may be accompanied by some pre-filtering of the source samples. For example, if only one sample per block is to be transmitted for each inactive block, then this sample may have a value which corresponds to the mean value of the sample values within that block.
It is preferred to pre-filter the source samples before sub-sampling so as to prevent aliasing in subsampled areas of the picture, thereby improving the quality of the decoded picture.
Analogue video signals are converted to digital signals at a high enough sampling rate to give a full-resolution picture by an analogue-to-digital converter 10. The digital video signal is then sub-sampled on a block-by-block basis by a sub-sampler 12 which also derives the appropriate pilot data signal 14 containing the sampling mode inform
REFERENCES:
patent: 3715483 (1973-02-01), Limb
patent: 4369464 (1983-01-01), Temime
patent: 4383272 (1983-05-01), Netravali
patent: 4575756 (1986-03-01), Furukawa
patent: 4691329 (1987-09-01), Juri
A High-Definition Satellite Television Broadcast System-MUSE (Kimura and Ninomiya), Journal of I.E.R.E., Oct. 1985, vol. 55, No. 10, pp. 353-356.
BBC Research Report (R. Storey et al.), Jun. 1986.
Practical Problems of Implementing a Conditional Replenishment Over an Error Prone Channel (M. Carr et al.) (date & source unknown).
A Video Encoding System with Conditional Picture-Element Replenishment (F. W. Mounts), B.S.T.S., Sep. 1969, pp. 2545-2552.
The 128th SMPTE Technical Conference Paper (G. Thomas), Preprint No. 128-149, Oct. 24-29, 1986.
Knee Michael J.
Sandbank Charles P.
Wells Nicholas D.
British Broadcasting Corporation
Britton Howard W.
O'Connell Robert F.
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