Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Patent
1996-03-08
1998-11-24
Chevalier, Robert
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
386 25, H04N 988, H04N 979
Patent
active
058419349
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for noise suppression in recorded luminance signals to be reproduced, in which a disturbed frequency range of the luminance signal is filtered out and limited to generate a subtraction signal, and the subtraction signal is subtracted from the luminance signal.
The invention also relates to a noise suppression circuit for video recorders in which the video signal recorded on a recording medium is processed as a luminance signal in a luminance channel and as a chroma signal in a chroma channel for reproduction, with a subtraction signal being formed from the luminance signal in a side branch composed of a filter and a limiter, said signal being capable of being supplied to a subtraction stage in the luminance channel to suppress a frequency range that causes noise.
2. Description of the Related Art
It is known that the signals reproduced by a video recorder exhibit significantly reduced quality as a result of noise. Therefore, known video recorders have noise suppression circuits that operate in both the horizontal and vertical directions. Frequency components that create significant noise are produced in the frequency-modulated luminance signal as a result of nonlinear distortions in the magnetic recording of the luminance (Y) and chroma (C) signals, which appear in the Y-useful signal following frequency demodulation. For example, the most noticeable noise develops in VHS recording of PAL signals at 1.25 MHz (corresponding to twice the mixed-down amplitude-modulated chroma signal carrier (627 kHz)). Known noise suppression systems therefore have a "frequency trap" at 1.25 MHz to suppress the undesired frequency components. For this purpose, in a side branch of the luminance channel, the luminance signal is filtered out at 1.25 MHz and subjected to a limitation. Filtration takes place by passing the luminance signal through a high-pass filter, then limiting it, and then subjecting it to a low-pass filtration. The high-pass filter and low-pass filter together form the limits of a bandpass. The limiter is effective for a high luminance signal level, so that the subtraction signal formed in the side branch has a relatively lower amplitude than the luminance signal when the luminance signal level is high. On the other hand, when the luminance signal level is low, the limiter is practically ineffective, so that high subtraction effectiveness occurs at 1.25 MHz.
This known noise suppression circuit has the disadvantage that because of the powerful suppressing effect at 1.25 MHz, useful low-amplitude signal components in particular (detail information) are suppressed, so that noise suppression always entails a reduction of detail information.
It is known from EP-A-0 464 772 that the limiter level in the side branch can be influenced as a function of the detected chroma signal level and the detected FM signal level. A high chroma signal level results in an increase in the limiter threshold, while a high FM signal level results in a drop in the limiter threshold. As a result, when the limiter threshold is increased, larger useful signal components are used to form the subtraction signal, and are therefore adversely affected in the luminance signal as a result.
SUMMARY OF THE INVENTION
Taking our departure from the statement of the problem of preserving detail information to the greatest extent possible, the method of the species recited at the outset according to the invention is characterized by the level of the subtraction signal following the limitation being varied as a function of the level of the corresponding chroma signal and/or the FM signal tapped from the recording medium.
On the basis of the statement of the problem as presented above, the noise suppression circuit recited at the outset according to the invention is further characterized by the level of the subtraction signal after passing through the limiter being varied as a function of the level of the chroma signal and/or the FM signal.
The invention that form
REFERENCES:
patent: 4232330 (1980-11-01), Heitmann
patent: 4695877 (1987-09-01), Matsumoto
patent: 4731660 (1988-03-01), Faroudja et al.
patent: 4998172 (1991-03-01), Kitazawa et al.
patent: 5063438 (1991-11-01), Faroudja
patent: 5097322 (1992-03-01), Kairhurst
Arnold Hans-Peter
Chmielewski Ingo
Rath Detlef
Chevalier Robert
Matsushita Electric Industrial Company
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