Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1989-06-16
1991-06-25
Groody, James J.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358167, H04N 514, H04N 5208, H04N 5213
Patent
active
050272101
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to noise reduction in television signals, in particular to noise reduction in high definition television signals such as, the example, High Definition Multiplexed Analogue Component (HD MAC) television signals transmitted as F.M.
2. Related Problems
High definition television signals have increased noise problems over conventional T.V. signals. For example, in HD MAC, picture signals transmitted for T.V. Pictures having a 5:3 "wide aspect" ratio have increased noise problems due to an increase in the signal baseband width, an increase in the de-compression ratio and the reduction of the viewing distance from 4 H to 3 H (where H=height of T.V. screen).
It would be desirable to apply noise reduction techniques to a high definition signal, in order to ensure that the reproduced signal is of satisfactory quality.
A further problem in this respect relates to the fact that in some cases it may be desirable to transmit a high definition T.V. signal together with a conventional signal, in the form of a "compound" signal. An example is HD MAC, which is, in fact, comprised of a conventional MAC signal together with additional information necessary to make up the high definition signal. A conventional MAC receiver will just utilise the conventional MAC signal, whereas a receiver adapted for HD MAC will utilise the complete signal to reproduce the high definition picture and sound.
Any noise reduction technique applied to reduce the added noise problems of a high definition signal should, therefore, be such as not to affect undesirably any conventional signal transmitted with the high definition signal in a compound signal, ie compatibility with transmission and processing of conventional signals such as may be processed by already existing techniques, needs to be ensured.
SUMMARY OF THE INVENTION
The present invention provides a method of processing a high definition television signal, comprising the steps of filtering the signal to give a high frequency sub-band and a low frequency subband, applying a non-linear pre-emphasis to the high frequency sub-band, re-combining and transmitting the signal, receiving the signal, filtering the received signal to provide high frequency and low frequency sub-bands, and applying a non-linear deemphasis to the high frequency sub-band.
The non-linear pre and de-emphasis applied to the high frequency sub-band advantageously gives adequate noise reduction to a high definition television signal to give an acceptable received signal.
Further, the frequency split and non-linear function are preferably arranged such that any conventional signal transmitted with the high definition signal is substantially unaffected by the processing, in the sense that the conventional signal may still be acceptably reproduced on a conventional receiver which is not arranged to be able to process a high definition signal. This is because in "compound" signals, such as HD MAC, it is only necessary to process the lower frequency transmitted signal in order to reproduce the conventional signal (below 8.4 MHz in the case of HD MAC), so that pre and de emphasis on the higher frequency band will not have a great deal of effect on the conventional signal.
The fact that the low frequency band does not have the pre/de emphasis characteristic applied thereto results in no appreciable degredation of the high definition signal either, as both noise and adjacent channel interference increase as frequency increases, and it is therefore the higher frequencies which are the most crucial as regards the noise in the transmitted signal.
The filter characteristics applied to the signal are chosen bearing in mind the effect on compatibility with conventional processing as against noise reduction effects for the high definition signal. The more of the signal is filtered for pre-emphasis (and noise reduction) the more compatibility is likely to be effected. A compromise is necessary.
The present invention further provides a receiver circuit
REFERENCES:
patent: 3288930 (1966-11-01), Johnson
patent: 3333055 (1967-07-01), Krause
patent: 4520396 (1985-05-01), Dischert et al.
patent: 4668988 (1987-05-01), Sasaki
patent: 4849826 (1989-07-01), Ohta
N. H. K. Technical Monograph, No. 32, Jun., 1982; J. Ishida; p. 6269.
Greening Wendy R.
Groody James J.
National Transcommunications Limited
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