Two electron beams are used to scan a striped color phosphor pattern arranged normal to the scan line in succession so as to increase the total amount of photon emission during the interval between successive line scans. The two beams are oscillated parallel to the scan line so as to increase the dwell time of impinging electrons on the phosphor stripe with a consequential increment in brightness. Beam sensing elements are located in a predetermined positional relationship with the phosphor stripes. Impingement of the scanning beams upon the sensing elements produces an index signal representing the nonlinearity which may be present in the horizontal deflection waveform, which signal is stored for the interval of a subsequent raster scan and retrieved nondestructively at the start of each line scan. The retrieved signal is modulated in frequency with a signal representing the time it takes for the beam to traverse the entire phosphor stripes to compensate for the so-called pincushion distortion. The frequency-modulated index signal is delayed so as to align it in phase with the start of each line scan. The phase-corrected index signal is used to sample a received primary color components in succession to provide a dot-sequential signal which is used to modulate the first beam. A predetermined delay time is introduced to the dot-sequential signal prior to the modulation of the second beam. Second beam sensing elements are located parallel to the phosphor stripes. Impingement of the scanning beams upon the sensing stripes results in two start-of-line index signals which are discriminated from each other by modulating the second beam with a pilot signal. The discriminated signals are compared in phase to compensate for a delay time error which may have been introduced to the intensity modulation of the second beam.