VIDEO SIGNAL GRADATION CORRECTOR

摘要

A video signal gradation corrector used in a television receiver or the like is disclosed which can prevent 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 or which can be realized with a small circuit scale. A histogram operating circuit (3) includes an average luminance level detecting circuit (99). A constant (100) is subtracted from an output signal of the average luminance level detecting circuit by a subtractor (101). The result of subtraction is multiplied by a constant by a constant-multiplication circuit (102). A lower-limit limiter circuit (103) 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. Also, the average luminance level and a constant (110) may be added by an adder (111). The result of addition is multiplied by a constant by a second constant-multiplication circuit (112) and is limited to a certain value by an upper-limit limiter circuit (113). An output signal of the upper-limit limiter circuit is provided as an accumulation stop luminance level, thereby enabling a gradation correction in which an excessive increase of the luminance level of the white side is prevented to suppress the blooming of a CRT.