Adaptive PAL - or NTSC - comb filter

Details Adaptive PAL - or NTSC - comb filter Adaptive PAL - or NTSC - comb filter

1991-04-19

1992-12-22

Groody, James J.

Facsimile and static presentation processing

Static presentation processing

Attribute control

H04N 978

Patent

active

051737680

DESCRIPTION:

BRIEF SUMMARY
This invention concerns comb filter apparatus for adaptively separating the luminance and chrominance components of a composite color television signal.


BACKGROUND OF THE INVENTION

In color television systems according to PAL or NTSC standards, a chrominance component in the form of a quadrature modulated color subcarrier, a luminance component, a blanking component and a synchronizing component are transmitted as a composite television signal. The luminance and chrominance components are frequency interleaved. At a receiver, the luminance and chrominance components are separated before being further processed prior to being applied to image reproduction apparatus. Such separation is also necessary in a video recorder system where the chrominance signal is subjected to special processing as is known.
It is known to pass the signal through a band pass filter to a line delay, and to produce a comb filtered chrominance signal by combining the signals from input and output of the line delay. A separated luminance component is provided by subtracting the comb filtered chrominance signal from the composite television signal. Such a comb filter produces an averaging over several image lines because signals of successive lines are combined. Thus, for example, in a signal with high frequency signal jumps (i.e., rapid transitions) or color transitions in the vertical direction, the comb filtered output signal may exhibit unwanted signal disturbances and artifacts. That is, the unwanted artifacts may appear in the comb filtered output signal when successive image lines contain different (uncorrelated) information such as produced by a color (phase) change or a rapid (amplitude) transition of a high frequency signal. This effect is indicated by the following table which illustrates the disturbed condition of several image lines after comb filtering.


______________________________________ line direct signal after comb filter ______________________________________ 2 . . . . . . . . .-.-.-.-.-.-.-.-.- (disturbed) 3 . . . . . . . . .-.-.-.-.-.-.-.-.- (disturbed) 4 . . . . . . . . . . . . . . . . 5 . . . . . . . . . . . . . . . . 6 .-.-.-.-.-.-.-.-.- (disturbed) 7 (disturbed) 8 ______________________________________
Certain improved transmission systems such as S-VHS video recorders and high definition television systems require a comb filter compatible with increased demands of such systems.
It is an object of the invention to develop a comb filter of the type described wherein signal disturbances and artifacts are significantly reduced or avoided while maintaining good signal separation.


SUMMARY OF THE INVENTION

In an illustrated preferred embodiment according to the principles of the invention, when conditions likely to cause the described disturbances or artifacts are present within an image structure of an input video signal, a subtraction stage which develops a separated luminance signal receives either a band pass filtered (non-comb filtered) chrominance signal or, in a PAL system under certain conditions, no chrominance signal instead of a comb filtered chrominance signal. The decision as to which of the signals is received by the subtraction stage is made by a switching circuit the operation of which is determined by prescribed parameters of the input signal. A control signal for the switching circuit is developed by a phase comparator network which responds to signals provided by a chrominance comb filter network including plural 1H delay circuits for developing 1H and 2H delayed output signals.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of an adaptive comb filter according to the present invention for processing a television signal according to PAL standards.
FIG. 1B is a block diagram of an adaptive comb filter according to the present invention for processing a television signal according to NTSC standards.
FIGS. 2 and 3 show additional details of apparatus according to the present invention for processing PAL and NTSC-type signals, respectively.

REFERENCES:
patent: 4050084 (1977-09-01), Rossi
patent: 4240105 (1980-12-01), Faroudja
patent: 4636840 (1987-01-01), McNeely et al.
patent: 4688080 (1987-08-01), Wagner
patent: 5047841 (1991-09-01), Robinson
patent: 5122867 (1992-06-01), Hagino
patent: 5134467 (1992-07-01), Kim

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