PULSED IMAGING, PULSE WIDTH MODULATION SCANNER FOR A TRI-LEVEL HIGHLIGHT COLOR IMAGING SYSTEM

A pulsed imaging, facet tracked, Raster Output Scanner utilizes pulse width modulation in conjunction with spatial filtering to form three exposure levels at the surface of a charged photoreceptor medium, one of the levels associated with a specific color. This type of scanner with a nominal video rendering experiences a color line growth in the process direction. The line growth problem is caused by a coherent optical effect. The resultant output print has bolded color lines in the process direction. Several techniques are set forth to compensate for this line growth. In a preferred technique, the video data stream is modified by locating or positioning video pulses representing white information at the start of an associated pixel time period. When the color pixel is imaged, it will therefore, always abut an adjoining white pulse and will be inhibited from spreading into the adjacent pixel period. Other techniques rely upon inversion of white pulses, or separation of white pulses into two signals, each segment moved to the beginning and the end of the associated pixel period. According to another technique, the input data stream is buffered and pixel groups examined to identify neighboring white and color signals. These signals are then either narrowed or in the case of a sequence of color signals, the lead and trail edge of the color signals are trimmed.