Video noise reduction system employing plural frequency bands

DETAILED DESCRIPTION The video noise reduction system 10 of FIG.
1 reduces noise of luminance signals by subjecting high frequency luminance signal components to coring and subjecting low frequency luminance signal components to frame recursive filtering.
The memory requirements for the frame recursive filtering are greatly reduced by sub-sampling the low frequency component before recursive filtering and then restoring the sample rate of the filtered signal to its original value (preferably by interpolation) after recursive filtering.
Memory savings result because there are fewer samples per line of the signal stored to implement the full field delay required for field recursive filtering.
Advantageously, in the specific example of the invention of FIG.
1, the memory savings achieved amount to seventy five percent (75%) of the memory which would otherwise be required for implementing recursive filtering using the sampling rate of the video input signal.
Memory savings of this substantial amount not only provide an obvious economic benefit but also provide a technical benefit as well in terms of improved reliability since the sub-sampled system delay requires are far fewer memory cells and thus there are fewer possibilities for memory cell failure.
It is a further feature of the noise reduction system 10 of FIG.
1 that the system is of general utility.
For example, it may be used in reducing noise in the luminance channel of a television receiver, a camera or a broadcast transmitter.
Other useful applications include reducing luminance signal noise in the record or playback circuits of a video cassette recorder (VCR) or a video tape recorder (VTR).
Additional benefits of the invention are obtained in video processing systems wherein a luminance signal band is split into high and low frequency components for purposes other than noise reduction.
Examples of such systems are described and discussed later with regard to the example of FIG.
2 of the drawing.
As will be seen, the memory savings for implementing field and frame delayed signals in such applications is very high because of the possibility of shared use of common signals