| 摘要 |
<p>Picture display device (1) comprising a cathode ray tube (2) whose display screen (4) is provided with parallel image lines (10) along which an electron beam (5) is scanned, and with pairs of first and second phosphorescent index elements extending along opposed sides of each image line (10). The device also comprises a pair of photodetectors (31,32) for generating index signals indicative of the amount of irradiation by the electron beam (5) of said index elements. An error signal is constructed based on a difference of said index signals for correcting the shape and/or the position of the electron beam (5) on the screen. The index signal of one of the photodetectors is indicative of the amount of irradiation of both the first and the second index elements (11, 12), which improves the detection efficiency of said detector and the signal/noise ratio of its index signal. This results in a better error signal and thus in a better image quality.</p> |
