US 5,289,282 AGranted

Video signal gradation corrector

AssigneeMatsushita Electric Industrial Co., Ltd.

InventorsToshiaki Tsuji, Atsuhisa Kageyama, Kiyoshi Imai

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Abstract

A video signal gradation corrector used in a television receiver or the like for preventing the destruction of the gradation of the black side and the floating of the luminance level of the black side and/or an excessive increase of the luminance level of the white side. The corrector can be realized with a small circuit scale. A histogram operating circuit includes an average luminance level detecting circuit. A constant is subtracted from an output signal of the average luminance level detecting circuit by a subtracter. The result of subtraction is multiplied by a constant by a constant-multiplication circuit. A lower-limit limiter circuit limits an output signal of the constant-multiplication circuit to a signal having a value not smaller than 0. An output signal of the lower-limit limiter circuit is provided as an accumulation start luminance level, thereby enabling a gradation correction in which the floating of the luminance level of the black side and the destruction of the gradation of the black side are prevented.

Claims6

Dependent claims

A video signal gradation corrector comprising:

a histogram memory for storing a luminance histogram of a video luminance signal;
a histogram operating circuit, receiving an output signal of said histogram memory, for extracting a feature of the luminance histogram from the output signal;
a limiter/adder circuit, connected to an output side of said histogram operating circuit, for processing data of said histogram memory;
an accumulation control register circuit connected to the output side of said histogram operating circuit;
a normalization control register circuit connected to the output side of said histogram operating circuit;
a histogram accumulation adding circuit, receiving an output signal of said histogram memory and an output signal of said accumulation control register circuit, for calculating a cumulative sum of said processed data of said histogram memory;
a cumulative histogram memory for storing said cumulative sum;
a look-up table operating circuit, receiving an output signal of said cumulative histogram memory and an output signal of said normalization data of said cumulative histogram memory;
and
a loop-up table memory for storing a result of said normalization performed by said look-up table operating circuit;
wherein said histogram operating circuit includes a circuit for detecting an average luminance level of an input luminance signal, operator means for performing an operation on the detected average luminance level using a constant, and a limiter circuit for limiting a lower limit value or an upper limit value of an output signal of said means.

8 more elements

Dependencies are inferred from the claim text.