EP0004728A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Noise reduction in electrical signals
Assignee: British Broadcasting Corp
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Filing: 1979-03-21
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Granted: —
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Expires: 1999-03-21
Abstract
Abstract Reduction of noise in an electrical, e.g. television, signal is achieved by comparing signals from successive scans to produce a difference signal. Low amplitude differences are assumed to represent noise and are attenuated. Differences above a predetermined level are assumed to represent movement and are not so attenuated. The attenuation is achieved by a multiplier (26) which receives as multiplier the output of a non-linear transfer characteristic element (24). The non-linear element receives the differences after rectification (100) and after passing through a variable-gain element (102). The non-linear element (24) is such that above a predetermined value a constant predetermined minimum attenuation factor applies. A noise measurement circuit (X) measures the noise present in the difference signal and controls the gain of the variable-gain element (102) accordingly. Several noise-measurement circuits may be provided. a selected one of which is used in dependence upon the magnitude of the input signal to the apparatus.
Inventors
- 👤 John Oliver Drewery
- 👤 Richard Storey
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-24 04:39
CPC Classifications
H; H04; H04N; H04N5/00; H04N5/14; H04N5/21
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
226 words
Apparatus for reducing the effect of noise in an electrical signal which is obtained by scanning, said apparatus comprising: input and output terminals (10, 18); a delay device (20) coupled to the output terminal for providing a delay time of substantially one scan; and means (12, 14, 16) coupled to the input terminal and to the output of the delay device for attenuating differences between the input signal during the current scan and the output signal during a preceding scan to provide an output signal which is applied to the output terminal; said means including a subtractor (12) coupled to the input terminal (10) and to the output of the delay device (20) for providing a difference signal, and an attenuation circuit (14) operative to provide a varying degree of attenuation in dependence upon said difference signal ' ; the attenuation circuit comprising: variable-gain means (102) coupled to the output of the subtractor (12); non-linear transfer characteristic means (24) coupled to the output of the variable-gain means; multiplier means (26) coupled to the output of the non-linear transfer characteristic means; and an adder (16) coupled between the output of the multiplier means and the output terminal; and wherein the apparatus further comprises: electrical means (X; or 248) responsive to a signal in the apparatus automatically to vary the value of the gain of the variable-gain means.
Claim 2
Dependent Claim
226 words
Apparatus for reducing the effect of noise in an electrical signal which is obtained by scanning, said apparatus comprising: input and output terminals (10, 18); a delay device (20) coupled to the output terminal for providing a delay time of substantially one scan; and means (12, 14, 16) coupled to the input terminal and to the output of the delay device for attenuating differences between the input signal during the current scan and the output signal during a preceding scan to provide an output signal which is applied to the output terminal; said means including a subtractor (12) coupled to the input terminal (10) and to the output of the delay device (20) for providing a difference signal, and an attenuation circuit (14) operative to provide a varying degree of attenuation in dependence upon said difference signal ' ; the attenuation circuit comprising: variable-gain means (102) coupled to the output of the subtractor (12); non-linear transfer characteristic means (24) coupled to the output of the variable-gain means; multiplier means (26) coupled to the output of the non-linear transfer characteristic means; and an adder (16) coupled between the output of the multiplier means and the output terminal; and wherein the apparatus further comprises: electrical means (X; or 248) responsive to a signal in the apparatus automatically to vary the value of the gain of the variable-gain means.
Claim 3
Dependent Claim
37 words
Apparatus according to claim 1, wherein the electrical means comprises noise-measurement means (X) coupled to the subtractor output for measuring the noise in the difference signal and for adjusting the variable gain element (102) in response thereto.
Claim 4
Dependent Claim
29 words
3* Apparatus according to claim 2, wherein the noise-measurement means comprises means for measuring the lowest value of the difference signal in defined periods, and averaging these lowest values.
Claim 5
Dependent Claim
49 words
Apparatus according to claim 2, including a plurality of separate noise-measurement means (X 1 , X 2 , X 3 ) for the variable-gain means, and means (248, 250) for selectively using one of the noise-measurement means in dependence upon the magnitude of the input signal to the apparatus.
Claim 6
Dependent Claim
51 words
Apparatus according to claim 1, wherein the electrical means comprises a plurality of separate controls (X 1 , X 2 , X 3 ) for the variable-gain means, and means (248, 250) for selectively using one of the controls in dependence upon the magnitude of the input signal to the apparatus.
Claim 7
Dependent Claim
25 words
Apparatus according to claim 4 or 5, wherein there are at least three controls associated with respective ranges of the amplitude of the input signal.
Claim 8
Dependent Claim
27 words
Apparatus according to claim 4, 5 or 6, wherein the electrical means is selectively enabled in dependence upon the presence of motion over the entire scanned picture.
Claim 9
Dependent Claim
32 words
Apparatus according to claim 4, 5, 6 or 7, wherein the electrical means is selectively enabled in dependence upon the presence of a change in the total nature of the scanned picture.
Claim 10
Dependent Claim
23 words
Apparatus according to claim 7 or 8, wherein the electrical means responds differently to apparent increases and decreases respectively in the noise level.
References Cited (Backward Citations)
No citation records indexed.
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