Automatic gain control apparatus

Details Automatic gain control apparatus Automatic gain control apparatus

1981-12-14

1984-09-04

Chin, Tommy P.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

358169, H04N 520

Patent

active

044700679

ABSTRACT:
An automatic gain control apparatus wherein red, blue and green channels of an input image signal are supplied directly, and indirectly through variable gain amplifiers, to black-level non-additive mixing circuits, respectively, and the channel signals of the input image signal are further supplied to a white peak non-additive mixing circuit for selecting a maximum level of the input image signals. Each of the gains of the variable gain amplifiers is controlled based on the selected maximum level for varying the knee slope in a manner such that the output image signal obtained from the black-level non-additive mixing circuits takes a white clip level at the peak level of the input image signal. Since any collapse of peak portions in the white level of the input image signal can be prevented regardless of a wide variation in a dynamic range of the input image signal. The apparatus is advantageously used in a television camera of a high latitude adapted for obtaining a shadowgraph of, for instance, a person standing indoors against a background of a bright sky or window.

REFERENCES:
patent: 3560645 (1971-02-01), Wallace
Automatic Beam Current Optimizer "IC" for Improvement of Latitude in Hand-Held TV Cameras, by K. Wakui, et al., NHK Laboratories Note, Ser. No. 227, Sep. 1978, pp. 1-10.

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