Television – Image signal processing circuitry specific to television – Noise or undesired signal reduction
Patent
1995-10-23
1998-04-28
Peng, John K.
Television
Image signal processing circuitry specific to television
Noise or undesired signal reduction
348618, 348623, H04N 521
Patent
active
057451885
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to information science and, more particularly, to an apparatus for suppressing interference in television video signals.
BACKGROUND ART
Known in the prior art is a non-linear television picture sharpness corrector comprising a controlled time constant low-pass filter and connected in series to the control input thereof a rectifier and a fixed time constant low-pass filter, the input of the rectifier being connected to the signal input of the controlled time constant low-pass filter (SU, A, 1140269).
In this apparatus, however, any attempt to reduce a noise level in television pictures which are of practical interest and which contain, in addition to background, some pels, leads to marked sharpness impairment of edges (otherwise termed outline) of these pels.
Also known in the art is a television picture sharpness corrector comprising a fast time constant low-pass filter, a relatively longer time constant low-pass filter, three electronic switches connected in series to said filters, and an analyzer. The inputs of all the filters and of the analyzer are combined. Combined are also all the outputs of the electronic switches having their control inputs connected to three outputs of the analyzer (SU, A, 1188904).
In this apparatus, any attempt to reduce noise level in television pictures which are of practical interest and which contain pels having sharp edges (otherwise termed outline), leads to impairment of picture sharpness, and vice versa, any attempt to improve picture sharpness leads to an increase in picture noise level.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide an apparatus for suppressing interference in a television video signal, which would permit considerable improvement in picture quality and, at the same time, in picture sharpness due to regeneration of the video signal.
This object is achieved by providing an apparatus for suppressing interference in a television video signal, the apparatus comprising connected in series an electronic switch and a low-pass filter, the apparatus according to the invention further comprising a high-pass filter having an input fed with a video signal, and an output connected to the signal input of the electronic switch, and a video signal front detector having an input connected to the output of the high-pass filter, while the output thereof being connected to the control input of the electronic switch.
In accordance with one aspect of the present invention, the video signal front detector comprises a full-wave rectifier connected in series with a squaring circuit.
In accordance with another aspect of the invention, the video signal front detector comprises a full-wave rectifier, a low-pass filter having an input connected to the output of the full-wave rectifier, an adder having inputs connected to the output of the full-wave rectifier and to the output of the low-pass filter, and a squaring circuit having an input connected to the output of the adder, the output of the squaring circuit being the output of the video signal front detector.
In accordance with yet another aspect of the invention, the apparatus comprises a signal delay unit having an input connected to the output of the high-pass filter, and an output connected to the signal input of the electronic switch.
In accordance with still another aspect of the invention, the video signal front detector includes two signal shaping channels having a common input which is the input of the video signal front detector, each channel comprising a squaring circuit in series with a monostable multivibrator, one of said channels comprising an inverter connected to the input of the squaring circuit, the outputs of the monostable multivibrators of channels being connected to the inputs of an AND circuit and of an OR circuit, the output of the AND circuit being connected to the input of another monostable multivibrator connected at its output to the input of a NOT circuit, the output of the OR circuit being connected to the input of a
REFERENCES:
patent: 4768094 (1988-08-01), Ichinoi
patent: 4837624 (1989-06-01), Heitmann et al.
patent: 5315396 (1994-05-01), Miyadera
patent: 5543926 (1996-08-01), Ezaki
Murrell Jeffrey S.
Peng John K.
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