TV receiver picture brightness control - uses low-pass filter to obtain average value for regulating black level

摘要

The TV set includes a circuit which controls the overall picture brightness. The luminance signal for the picture is used to regulate the overall brightness or the brightness of the darkest or black areas of the picture. The circuit uses a low-pass filter to obtain an average value for the picture brightness; it consists of a resistor (31) connected to an earthed capacitor (32). When the overall picture brightness is low, the 'black' value is raised. It has an intermediate value with pictures of medium brightness and a low value when the picture is very bright.