Noise reduction circuit

Details Noise reduction circuit Noise reduction circuit

1989-01-10

1990-10-02

Chin, Tommy P.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

358 36, H04N 5213

Patent

active

049611135

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
This invention relates to a noise reduction ciruit 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, one shown in FIG. 6 is hitherto known.
In FIG. 6, input video signal S.sub.I fed at an input terminal 1 and containing noise passes through a low-pass filter 2 to become signal S.sub.L, the low frequency component in which noises has been removed. Signal S.sub.L is supplied to an adder 3. The above input signal S.sub.I is also supplied to a high-pass filter 4 to obtain signal S.sub.H1, the high frequency component containing the noise component from high-pass filter 4. Signal S.sub.H1 is supplied to a limiter 5. Limiter 5 has the input/output characteristic as shown in FIG. 7, in which the output signal becomes zero when the level of input signal is within the range between V.sub.1 and V.sub.Z. Accordingly, a signal having a level above the above range of V.sub.1 to V.sub.2, that is, signal S.sub.H2 in which noise component has been removed, is obtained from the above high frequency component signal S.sub.H1 at limiter 5. Signal S.sub.H2 is supplied to adder 3 to be added to signal S.sub.L in which the above high frequency component has been removed. As a result, output signal S.sub.O in which noise is reduced is obtained at an output terminal 6.
Further, a conventional noise reduction circuit using a delay circuit such as a field memory or a which frame memory is known, in which difference signal between the signal obtained by delaying input signal S.sub.I through a delay circuit such as a field memory or a frame memory, and input signal S.sub.I a is obtained, and the difference signal is subtracted form input signal S.sub.I. Since the above difference signal is considered a noise component when there is no movement within a field or a frame in input signal S.sub.I, noise can be reduced by that noise component being subtracted from input signal S.sub.I. Accordingly, this circuit is provided with a movement detection ciruit for detecting movement is input signal S.sub.I. When movement is detected, the above difference signal is considered noise component so inhibited from being subtracted from input signal S.sub.I.
Another noise reduction circuit is proposed in Patent Kokai No. Sho 55-127737 by the present applicant.


DISCLOSURE OF THE INVENTION

As described above, in the noise reduction ciruit in FIG. 6, all low level components (ones within the range of V.sub.1 to V.sub.2) in high frequency signal S.sub.H1 of input signal S.sub.I are condsidered noises. In practice, however, it may be that a signal component is contained within the range of V.sub.1 to V.sub.2. In that case, if the signal component is removed by limiter 5, the definition of image is lowered.
The noise reduction circuit using a field memory or a frame memory as described above has the further defects that it requires a large capacity memory in order not to lower the definition of image, and the circuit configuration becomes larger because the movement detection circuit is required.
For overcoming the above defects, in a noise reduction circuit according to the invention, a video signal is divided into a first signal having the low frequency component and a second signal having the high frequency component, the second signal is divided into a third signal having an amplitude more than a predetermined value and a fourth signal having an amplitude less than the predetermined value, a fifth signal is obtained by applying a noise reduction process using a delay circuit to the above fourth signal and the above first, third and fifth signals are added.
In the noise reduction circuit according to the invention, the noise reduction process using a delay circuit is effected as to the signal having an amplitude less than the predetermined value in the signal of the high frequency component, i.e. the fourth signal, so that the signal component of high frequency which is removed together with the noise component in a

REFERENCES:
patent: 3715477 (1973-02-01), Olson et al.
patent: 4009334 (1977-02-01), Sypula
patent: 4015076 (1977-03-01), Ishiodori
patent: 4268855 (1981-05-01), Takahashi
patent: 4393396 (1983-07-01), Raven et al.
patent: 4709269 (1987-11-01), Ozaki

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