Control system for a variable-resolution raster output scanner

A method of controlling a raster output scanner having a light source for emitting a modulated beam according to digital data at a pixel clock rate and a rotatable polygon mirror for causing the modulated beam to scan across a photosensitive surface in a fast-scan direction, the photosensitive surface moving in a slow-scan direction substantially perpendicular to the fast-scan direction, comprising the steps of:

• operating the scanner by modulating the beam at a pixel clock rate and causing the modulated beam to scan across the photosensitive surface;
• measuring the pixel clock rate and the rotational velocity of the polygon mirror in real time as the scanner is operating;
• determining a clock command value as a function of a value related to the real-time measured pixel clock rate and a value related to a desired resolution in the fast-scan direction and a desired resolution in the slow-scan direction of an image to be created on the photosensitive surface;
• controlling the pixel clock rate in response to the clock command value;
• determining a polygon command value as a function of the value related to the real-time measured pixel clock rate, a value related to a desired resolution in the fast-scan direction of an image to be created on the photosensitive surface, and a value related to the real-time measured rotational velocity of the polygon mirror;
• and
• controlling the rotational velocity of the polygon mirror in response to the polygon command value.