An image forming apparatus includes a modulation data storage, a pulse width modulator, and an optical writing mechanism. The modulation data storage stores different gray-scale pulse sets. Each set includes gray-scale pulses having pulse widths different from each other in steps of a predetermined value...http://www.google.com.tw/patents/US7215353?utm_source=gb-gplus-share專利 US7215353 - Method and apparatus for image forming capable of effectively controlling a light beam with a pulse width modulation
