| 摘要 |
A gamma correction circuit superimposes gamma reference pulse on the input video signal and, after further superimposing this on a pedestal signal, gamma corrects the signal to the maximum value using a fixed gamma correction circuit and sends this corrected signal together with an uncorrected signal to a variable gamma correction circuit. The variable gamma correction circuit controls the input mixing ratio in response to the correction value control voltage to thereby determine the gamma correction value. After the gamma-corrected video signal has been clamped by the clamp circuit, it is supplied to the sample-and-hold circuit which detects the gamma reference pulse level superimposed on the input video signal, and holds it. This held voltage is added by the gamma correction value control circuit to the gamma correction control input and is sent to the variable gamma correction circuit as the correction value control voltage. In other words, a feedback loop for the variable gamma correction circuit is formed of the clamp circuit, sample-and-hold circuit and the correction value control circuit.
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