Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1989-01-10
1991-04-02
Chin, Tommy P.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358 36, H04N 5213
Patent
active
050050818
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field:
This invention relates to a noise reduction circuit for video signals used in, for instance, a television receiver.
2. Background Art
As a noise reduction circuit used in a television receiver or the like, those shown in FIGS. 9 and 10 are hitherto known in which a delay circuit such as a field memory (or a frame memory) is used.
FIG. 9 shows one forming an open-loop, in which input video signal S.sub.I containing noise and fed at input terminal 1 is supplied to adders 2 and 3, and is also supplied to A/D converter 4 for converting it into a digital signal. It is then written in to field memory 5, which functions as a delay circuit. The digital signal read from memory 5 is converted back into an analog signal S.sub.I1 by D/A converter 6. Accordingly, this analog signal S.sub.I1 is delayed by a field in relation to the above signal S.sub.I.
This signal S.sub.I1 is supplied to adder 2 and subtracted from the above signal S.sub.I The difference signal S.sub.I -S.sub.I1 between signal S.sub.I and signal S.sub.I1 is obtained from adder 2 and is supplied to movement detection circuit 7 and to multiplier 8. The above difference signal S.sub.I -S.sub.I1 is considered a noise component if there is no movement in input signal S.sub.I within a field. In this case. difference signal S.sub.I -S.sub.I1 is multiplied by coefficient k at multiplier 8 in accordance with detection signal S.sub.M from detection circuit 7 and then subtracted from signal S.sub.I at adder 3. Therefore, output signal S.sub.o in which noises are reduced is obtained from adder 3 at output terminal 9.
When a movement is detected by movement detection circuit 7, the above difference signal S.sub.I -S.sub.I1 is considered to contain a movement component so multiplier 8 reduces the value of K in accordance with signal S.sub.M from detection circuit 7 to reduce the quantity of the movement component subtracted at adder 3.
Movement detection circuit 7 detects the level of the above difference signal S.sub.I -S.sub.I1, and produces, detection signal S.sub.M with which coefficient K of multiplier 8 is controlled. This movement detection circuit 7 may also be placed to compare the input signal and output signal of field memory 5 with each other as shown by dotted lines in the drawing.
FIG. 10 shows an instance forming a closed loop, in which signal S.sub.I1 that a part which is output signal S.sub.o delayed by a field in memory 5, is subtracted from signal S.sub.I at adder 2 and that difference signal S.sub.I -S.sub.I1 is passed through multiplier 8 and subtracted from signal S.sub.I at adder 3. Thus, noise contained by signal S.sub.o is gradually removed by feeding back signal S.sub.o, after delaying it by a field, so that S.sub.o is obtained from adder 3 with noise reduced.
A noise reduction circuit using a frame memory as disclosed by Patent Kokai Sho 54-157429 is known.
DISCLOSURE OF THE INVENTION
The noise reduction circuit using a delay circuit such as a field memory (or a frame memory) as described above has need of both a memory of large capacity, to avoid lowering the definition of image, and a movement detection circuit so it has a defect in that the circuit configuration becomes large.
To overcome such a defect, in a noise reduction circuit according to the present invention, a difference signal is obtained which is the difference between a signal obtained by passing the original video signal through a low frequency shut-off filter and a limiter and the signal obtained by passing that signal through a field or frame delay circuit. The difference signal is then subtracted from the original video signal.
According to the noise reduction circuit of the present invention the part of the signal having an amplitude lower than a predetermined value is taken out by the limiter from the high frequency component of the signal obtained from the filter, and the difference in the field or frame of this signal is detected. Therefore, noise reduction is effected without lowering the definition. A movement component is not co
REFERENCES:
patent: 4571613 (1986-02-01), Fukuda
patent: 4709269 (1987-11-01), Ozaki
patent: 4768498 (1988-05-01), Yamanishi
patent: 4860105 (1989-08-01), Sakaguchi
patent: 4885639 (1989-12-01), Nakata
patent: 4961113 (1990-10-01), Okada
patent: 4962434 (1990-10-01), Matsuo
Chin Tommy P.
Shaw, Jr. Philip M.
Sony Corporation
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