Method for holding black level constant - holds black level during A=D conversion of video signal and compares to nominal black signal

摘要

The video input signal after filtering and pre-amplification, is fed through a controlled black value hold stage (2) to an analogue-digital converter (4). The converter provides a digitalised video signal on its output and its digital value is detected by a binary comparison with the binary value of the nominal black signal. A setting signal is then obtained from the results of the comparision for the cases, it smaller than nominal and larger than nominal for controlling the deviation of the black from its nominal value in the black value hold stage. USE/ADVANTAGE - For TV industry. Reliable and accurate.