Circuit including clipping and non-linear processing means for correcting the tone of an image signal

摘要

A circuit for correcting a tone of a brightness signal generated by a television camera including an upper limiter for clipping off an upper portion of the brightness signal higher than an upper threshold level, and a lower limiter for clipping off a lower portion of the brightness signal lower than a lower threshold level which is automatically changed in accordance with a peak value of the black level of the brightness signal. A middle level brightness signal produced by the lower limiter is processeed by a non-linear circuit and then a difference between a non-linearly processed bright signal and the middle level brightness signal is derived to produce a tone correction signal. After the polarity and gain of the tone correction signal are manually adjusted, the tone correcting signal is added to the input brightness signal. In this manner the tone of a television image displayed on a television monitor screen can be corrected exclusively in a dark area without affecting the tone in a bright area. When the tone correction signal has the negative polarity, the dark background can be further darkened without decreasing the brightness in the bright area to attain a special production effect.