Abstract: Pre-polygon optics are provided which consist of a compact design such that the number of pre-polygon elements in the pre-polygon optics is reduced while achieving desired light beam characteristic. The pre-polygon optics may consist of a hybrid toroidal diffractive optical element, refractive cross-cylindrical optical elements, refractive spherical and cylindrical optical elements, a refractive sagittal cylindrical optical element or a refractive tangential cylindrical optical element. Accordingly, advantages such as lower cost and ease of alignment are achieved.

Abstract: The present invention is a method and apparatus for improving the depth of focus in a raster output scanner (ROS), and more particularly to a system for maximizing the line separation depth of focus of a multispot ROS while maintaining the system common depth of focus. In a preferred design for a ROS-based system, the system common depth of focus (system common DOF) is maximized, where the system common DOF is characterized as the depth-of-focus over which all performance parameters are met. More specifically, the performance parameters are intended to include the following five factors: (1) scan and cross-scan spot size; (2) wobble; (3) differential bow; (4) line separation; and (5) scan linearity. Maximizing the system common DOF means to maximize the depth-of-focus while at all times meeting or exceeding the performance requirements for the five listed parameters. The optical system design achieves a desirable system common DOF while maintaining a line separation of 127 .mu.m (1/200 inch).

Abstract: In an overfilled polygon ROS architecture, fast scan jitter is reduced by uniformly illuminating the overfilled facets. In one embodiment, the collimator lens is designed with a long focal length to transmit only the more uniform central portion of the Gaussian shaped intensity profile output of a laser diode. In another embodiment, the light level at the polygon facet is made uniform by introducing a variable transmission filter along the optical path.

Abstract: A hybrid halftone cell selection method enables selection of gray levels in halftone printing algorithms to minimize the effects of noise resulting in nonuniformities, such as, for example, halftone banding. The method requires selection of hybrid halftone cells possessing structures wherein the total number of gray pixels are limited. The number of gray pixels having any given intermediate reflectance level in any halftone cell is also limited. The cell selection method thus reduces the number of TRC gray steps to some minimum required number by eliminating the most noise sensitive cells (i.e. those cells having the highest percentage of gray level pixels). The intermediate reflectance values of the gray pixels in the selected cells are then selected to produce uniform gray steps and reduce variability in the TRC.

Abstract: The pre-polygon scanning path length of a raster output scanning system is reduced by replacing a required cylinder lens, or lenses, with two cylindrical mirrors. One mirror with a negative, concave surface and a second positive cylindrical mirror. The first mirror directs the light beam to the second mirror. The second mirror directs the light onto the facets of a rotating polygon to form a focused beam in the vertical axis of the polygon. The function of the two cylindrical mirrors is to act as a telephoto lens to properly focus the image of the laser at the polygon facet while reducing the total pre-polygon path length.