Edge Inference with Applications to Antialiasing

Abstract

An edge, when point-sampled for display by a raster device and not aligned with a display axis, appears as a stair-case.This common aliasing artifact often occurs in computer images generated by two- and three-dimensional algorithms. The precise edge information often is no longer available but, from the set of vertical and horizontal segments which form the staircase, an approximation to the original edge with a precision beyond that of the raster may be inferred. This constitutes a smoothing of the staircase edge. Among other applications, the inferred edges may be used to reshade the pixels they intersect, thereby antialiasing the inferred edges. The antialiased inferred edges prove a more attractive approximation to the real edges than their aliased counterparts. Presented here are algorithms for the detection and smoothing of edges and the filtering of an image in accordance with the inferred edges.