Antialiasing with Line Samples

Abstract

Antialiasing is a necessary component of any high quality renderer. An antialiased image is preduced by convolving the scene with an ant-ialias-ing filter and sampling the remit, or equivalently hy solving the antialz'asing integral at each pixel. Though methods for analytically computing this integral exist, they require the continuous two-dimensional result of visihle—smiace computations. Because these computations are expensive, most renderers use supersamph’ng, a discontinuous approximation to the integral. We present a new algorithm, line sampling, combining a continuous approximation to the integral with a simple y'isible—sm'face algorithm. Line sampling provides high quality antialiasing at significantly lower cost than analytic methods while ayoiding the visual artifacts caused by supe1s‘1mpli11g’s discontinuous nature. A line sample is a line segment in the image plane, centered at a pixel and spanning the footprint of the antialiasing filter. The segment is intersected with scene polygons, visible subsegments are determined, and the antialiasing integral is computed with those subsegments and a one-dimensional reparameterization of the integral. On simple scenes where edge directions can he precomputed. one correctly oriented line sample per pixel suffices for ant-ialiasing. Complex scenes can he antialiascxl by combining multiple line samples weighted according to the orientation of the edges they intersect.