Raster shape synthesis by direct multi-level filling

Abstract

A method of synthesizing multi-level raster shapes directly from outlines describing ideal shapes is disclosed. A raster shape suitable for approximating the ideal shape in a raster display device is synthesized by dividing a plane into a plurality of pixel areas according to a pixel grid, then by representing the shape as one or more arcs in the plane, where the arcs collectively, and in conjunction with an insideness criterium, divide the plane into an inside region and an outside region, and then by separating the pixels into inside pixels, outside pixels, and boundary pixels. The raster shape comprises coverage values assigned to each pixel in the plane, where inside pixels are assigned a coverage value of 1, outside pixels a coverage value of 0 and the boundary pixels a coverage value between 0 and 1 approximating the degree to which the boundary pixel is covered by the inside of the outline. Initially, boundary pixels are assigned a coverage value of 0 or 1 based on a pixel-coverage criterium, and then it is corrected by a correction value resulting in a coverage value between 0 and 1. The correction value for a pixel might be a numerical value indicating the fraction of the pixel covered by the correction region; the correction value may also depend on the geometry of the correction region represented by the valve and the region's location within the pixel. The correction region of a boundary pixel is the signed difference between the region represented by the initial coverage value assigned to the pixel and the actual region of the pixel covered by the inside of the outline.