Black level detecting circuit of video signal

Details Black level detecting circuit of video signal Black level detecting circuit of video signal

1998-03-02

1999-07-06

Kostak, Victor R.

Television

Cathode-ray tube display automatic black level bias control

348673, H04N 568

Patent

active

059203510

ABSTRACT:
A black level detecting circuit compares an input video signal with a current minimum value of input video signals, then detects a difference between the input signal and the current minimum value when the input value is smaller than the current minimum value, and then outputs the detected difference only during a detecting period of the black level, then corrects the minimum value by using this output for renewing the current minimum value, and finally outputs this renewed minimum value as a new minimum value of the input video signal. The black level detecting circuit also latches the minimum value during the vertical blanking pulse and initializes the minimum value during a vertical blanking period so as to detect a black level of the input signal. As such, the black level detecting circuit measures the black level only during a video period, thereby reducing detection errors due to noises, and also an automatic initialization of the minimum value during a blanking period can contribute to a more stable detection of the black level. The black level detected can be used effectively as a control signal over picture quality for each field or each frame.

REFERENCES:
patent: 3976836 (1976-08-01), Wheeler
patent: 4587554 (1986-05-01), Tamura et al.
patent: 5410222 (1995-04-01), Flickner

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