Circuit for making a crt display a tv picture for a copy with dots

Abstract

In order to make a cathode-ray tube display a television picture for providing a copy thereof, as in a computer output device, a circuit substitutes dot-superposed signals for those portions of a television signal which provide half-tone areas of the picture. For a color television signal, the dot-superposed signals are derivable by storing the television signal for one field of frame and repeatedly reading the stored signal. The read-out signals are preferably emphasized at the subcarrier frequency. For a monochrome television signal, a signal is generated and inversed. For a generated signal of an even multiple of the horizontal scanning frequency, a phase-adjusted signal is produced by selecting either the generated signal in every other line period of the respective frames and the inversed signal in the remaining line periods or the generated and inversed signals in every other field and the remaining fields, respectively. For a generated signal of an odd multiple of the line frequency, the phase-adjusted signal is produced by selecting the generated and inversed signals in every other frame and the remaining frames. Responsive to the phase-adjusted signal, the television signal is modulated to have a maximum amplitude at the black and white levels and a minimum amplitude at the above-mentioned portions. For modulation, the television signal may be preliminarily modified to have a minimum level at the black and white levels and a maximum level at a level bisecting the black and white levels.