PURPOSE: To correct gradation without letting the black level of video be viewed like floating even for signals for which input signals are concentrated in a dark part relating to a gradation correction circuit for effectively utilizing the cathode-ray tube of a small dynamic range.
CONSTITUTION: This gradation correction circuit is provided with a cumulative histogram circuit 1 for taking a cumulative histogram at every field of inputted video signals, dividing it by all the sample number, normalizing it and outputting it, an APL detection circuit 6 for detecting the APL of the inputted video signals, a first adding circuit 5 for adding the output signals of the APL detection circuit 6 to the input signals, a first subtracting circuit 2 for subtracting the output signals of the first adding circuit 5 from the output signals of the cumulative histogram circuit 1, a first multiplying circuit 3 for multiplying the first subtracting circuit 2 by a constant and a second adding circuit 4 for adding the output of the first multiplying circuit 3 to the inputted video signals.
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IZAWA YOSUKE
SAKASHITA HIROHIKO
FUJITA MASAAKI
