Adjustment of TV receiver colour reference levels - uses circuit switching into chrominance signals during frame suppression period

摘要

A TV receiver operating under the SECAM system has a circuit which adjusts the colour reference levels which is switched at an instant corresponding to a non visible part of the image. A TV receiver for the SECAM system has a colour reference adjustment circuit comprising a pass band filter (13) through which reference signals are switched (4) corresponding to rest frequencies (6, 7). These frequencies are switched (2) into the chrominance signals (1) at non visible parts of the image. The switching is performed during a fraction of the frame suppression periods to insert reference levels into the colour difference (B-Y, R-Y) signals.