Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1988-01-25
1990-02-20
Peng, John K.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358140, 358 15, 375 38, H04N 704, H04N 701, H04N 1112
Patent
active
049031252
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and apparatus for conveying information signals, particularly (but not exclusively) television signals. In general television signals are conveyed from a source to a receiver by way of a medium. The medium may be a transmission medium (e.g. terrestrial or satellite radio, cable) or a storage medium (e.g. video cassette, optical disc). Many different sources are now available including studio and portable cameras, computers, tele-cine apparatus, and so on. There is a concomitent tendency for standards to proliferate if only to match the different bandwidths and/or signal to noise performances of different systems. Such proliferation is clearly undesirable.
A related problem arises in that it is often not possible to specify the bandwidth or signal to noise performance which is appropriate in a given system. There may vary in dependence upon fluctuating transmission medium characteristics, size of receiving antenna in the case of satellite radio transmission, changes in transmitter power, and so on. For brevity, the remaining description refers simply to bandwidth, although it is frequently the signal to noise performance which is actually the determining factor.
The object of the present invention is to provide a solution to the problems which thus arise, by means of a method and apparatus which allow adaptable standards to be set up within a universal system.
According to the invention in one aspect, there is provided a method of conveying television signals from a source to a receiver by way of a medium, wherein signals from the source are segregated into a plurality of channels corresponding to progressively less visually significant information, a composite signal is formed, for conveyance by the said medium, by a reversible combination of component signals from the said channels with the powers of the component signals varying directly in dependence on the significances of the channels, and wherein, at the receiver a number of the component signals are recovered from the composite signal conveyed to the receiver by the said medium and a television signal is formed from the recovered signals.
Such a method may be employed in the content of a heirarchy of standards, comprising a prime, maximum bandwidth standard and other standards requiring progressively less bandwidth, including a basic, minimum bandwidth standard. When the prime standard is appropriate, all the channels are employed at the source but, when lesser bandwidths are required, channels are progressively dropped, starting from the least significnt channel. The conveyed signals can include a label which informs the receiver as to the number of channels which have been employed.
The receiver can recover all of the component signals included in the conveyed composite signal. However the receiver does not have to recover all of the component signals. If for example the medium is noisy for any reason (fringe area reception, small receiving antenna, and so on) the receiver may ignore at least the least significant component signal included in the conveyed signal. This will enhance the received picture by cutting out displayed noise, although the picture will naturally have reduced detail.
The invention will be described in more detail, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a diagram showing how different pixel resolutions are employed in a television frame,
FIG. 2 is a diagram showing how a coarsest resolution pixel is progressively subdivided,
FIG. 3 is a block diagram of apparatus embodying the invention, and
FIG. 4 is a graph used in explaining receiver performance in direct broadcasting by satellite.
In order to allow a common transmitting and receiving system for all standards, it is desirable that the higher bandwidth standards are all subsets of the preceding standard. In particular, in the spatial domain, each standard should employ a finer sampling grid than the preceding standard but which contains the sampling points of the preceding standard.
The in
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British Broadcasting Corporation
O'Connell Robert F.
Peng John K.
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