Bandwidth compression for television signals

Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry

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Details

358138, H04N 712

Patent

active

049424661

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention is concerned with bandwidth compression for television video signals.
If High Definition Television (HDTV) is to become a practical proposition, then some method of transmitting it to the home is required. It is widely assumed that such transmissions will be via satellite, since spare radio spectrum is not available elsewhere. The principal problem in this case is the extremely wide bandwith of the original HDTV signal--possibly in the region of 40 to 50 MHz for the combined luminance and chrominance information. Such bandwidths can not be accommodated in the 12GHz DBS (digital broadcast by Satellite) band.
The high transmission bandwidth required for HDTV will cause problems not only for terrestrial and satellite broadcasting but also for signal dissemination by other media such as videotape, videodisc and cable. Some form of bandwidth reduction is required in order to overcome these difficulties.
Methods of bandwidth reduction have been described which use sub-Nyquist sampling with ore-filtering in one, two and three dimensions. More recently motion adaptive pre-filtering techniques have been described, are for example NHK Laboratory Note No. 304, 1984, NINOMIYA et al "A single Channel HDTV Broadcast System" and a paper presented by FUJIO, SUGIMOTO and NINOMIYA at the 14th International Television Symposium, Montreux, June 1985, "HDTV Transmission Method (MUSE)". This system is based upon the removal, by filtering, of image frequency components that are assumed to be of little use to the eye. The filtered signal has a much reduced bandwidth and can be re-sampled at a lower rate for transmission.
The use of motion-adaptive spatial sub-sampling can yield impressive reductions in transmitted bandwidth. Still areas of the picture are transmitted at full resolution but with the information being distributed over many different television fields. Moving areas are transmitted at a reduced resolution, taking advantage of the eye's alleged inability to perceive detail in moving objects. This is the approach used in the NHK's MUSE system (described in the above papers) and which has an objective bandwidth compression factor of 4:1, leading to a final transmission bandwidth of only 8.1 MHz. This system has given results that, while in general encouraging, nevertheless can be variable and unpredictable. We have appreciated that the system performance will differ from receiver to receiver and also vary as reception conditions, and hence the carrier to noise ratio, changes, and that this arises because the system detects which areas of the scene are moving and which stationary at every receiver. Furthermore, the system is relatively expensive in requiring movement detection circuitry at every receiver.


SUMMARY OF THE INVENTION

The invention is defined in the claims below to which reference should now be made.
In a preferred embodiment of the invention, described in more detail below, an analogue video signal to be bandwidth reduced is subjected to two types of filtering in parallel, namely temporal filtering which is appropriate where stationary portions of the picture are concerned, and spatial filtering which is appropriate where moving portions of the picture are involved. Which filter output is used at any instant is dependent upon the picture content, and the filtering control signal is not only used at the transmitter/encoder but is also transmitted as a digital signal associated with the analogue video transmission signal to the receiver/decoder.
The preferred system enables a highly detailed image to be transmitted in stationary and slowly moving areas of the picture. The remaining areas contain poorly correlated information such as revealed detail, shot changes and erratic motion. These areas are transmitted at a lower definition since the human visual system genuinely requires less detail when image detail is poorly correlated from field to field.
The reduced bandwidth signal consists mainly of analogue sub-sampled picture data, but also contains a digital conro

REFERENCES:
patent: 4542411 (1985-09-01), Imanaka et al.
patent: 4665436 (1987-05-01), Osborne et al.
patent: 4691329 (1987-09-01), Juri et al.
patent: 4706265 (1987-11-01), Furukawa
patent: 4713688 (1987-12-01), Guttner
patent: 4745458 (1988-05-01), Hirano et al.
NHK Laboratories Note, No. 304, Sep. 1984.
HDTV Transmission Method, Fujio et al., (no date).
Improved Display Techniques Based on Sequentially-Scanned Studio and Transmission Standards, C. K. P. Clarke.
HDTV Motion Adaptive Bandwidth Reduction Using DATV, R. Storey.
Video-Rate Image Correlation Processor, Pearson et al., (1977).
BBC Research Department Report-BBC RD 1986/5, R. Storey.
BBC Research Department Report-BBC RD 1983/8, A. Roberts.

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