Contrast control based on mean and deviation values

Details Contrast control based on mean and deviation values Contrast control based on mean and deviation values

1989-10-20

1992-03-24

Groody, James J.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

358236, 358 39, H04N 557

Patent

active

050993305

ABSTRACT:
A contrast control circuit for processing a video signal comprises a digital video-signal processing circuit which detects a mean value of a digital luminance signal of the digital video signal and subtracts the detected mean value from the digital luminance signal in order to obtain a difference signal, and a limiter circuit which receives and limits the difference signal to a range defined by predetermined upper and lower limits. And a digital video-signal processing circuit including amplifier means for amplifying a digital luminance signal, obtains a mean value of one field of the digital luminance signal or of one field of the digital luminance signal amplified by the amplifier means, calculates deviations of the digital luminance signal or of the digital luminance signal amplified by the amplifier means from the obtained mean value, accumulates the deviations calculated for the period of one field in order to obtain a contrast value, and controls the gain of the amplifier means on the basis of the obtained contrast value.

REFERENCES:
patent: 4231065 (1980-10-01), Fitch et al.
patent: 4253110 (1981-02-01), Harwood et al.
patent: 4635119 (1987-01-01), Baker
patent: 4654710 (1987-03-01), Richard
patent: 4745461 (1988-05-01), Shirai et al.
patent: 4785352 (1988-11-01), Burrowes et al.
patent: 4829381 (1989-05-01), Song et al.
patent: 4937671 (1990-06-01), Engel

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