Visibility system for SECAM-TV colour bars - has colour-level for yellow and blue colour-bar region

摘要

The visibility system improves the visibility of the edges of colour bars in a SECAM television system. The colour bars are produced by video-frequency signals reduced to 75% of a standard level and coded according to SECAM standards. In addition to the 75% reduction the colour signals are also limited to approx. 30% (preferably 37.5%) w.r.t. 100% white level in the yellow and blue colour-bar regions and from amplitudes in the direction of the black level (0%). The limiting is down by two transistors coupled emitter-to-emitter with their collector/emitter paths in parallel. The colour-bar signals are applied to one base, the yellow to blue signals to the other base, and the output is taken from the emitters.