PICTURE SIGNAL PROCESSING UNIT

PURPOSE:To obtain a picture with smooth gradation by generating a pulse width modulation signal with a different phase from a triangle wave threshold level whose phase differs from each other and selecting the output for each subscanning line and recording a picture. CONSTITUTION:An input picture signal IDT 901 of one line in the main scanning direction synchronously with a picture element clock is inputted to a gradation correction table 101, in which the gradation is corrected and the signal is converted into an analog signal at a D/A converter 103. The signal is inputted to comparators 107,108 and compared with triangle wave threshold level signals SW1, SW2 and pulse width signals 910,911 in response to the levels of an analog signal are outputted. Thus, the signal SW1 is deviated by 180 deg. from the signal SW1. The pulse width modulation signals 910, 911 obtained by the comparators 107, 108 are inputted to a selector 110 and a laser is lighted or goes off by a time in response to the pulse width by using the signal 111. Since the gradation characteristic of the pulse width modulation system is improved in this way, the visual gradation characteristic is improved.