Abstract: A color television image presentation cathode-ray tube with running indexing elements as the beam scans horizontally across the stripes, an index signal is produced representative of beam position with respect to the different colored stripes. The minimum intensity of the beam while scanning the image-presentation portion of the cathode-ray tube is automatically maintained at a near-optimum value sufficient to produce an adequate strength of indexing signal without unduly illuminating those portions of the picture intended to be black. When the strength of the beam current would otherwise tend to become too small, the blackest part of the picture is shifted in the direction to increase the beam intensity and the indexing signals.