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.