Continuous anti-aliased rotation and zoom of raster images

Abstract

Raster graphics images are difficult to smoothly rotate and zoom because of geometric digitization error. A new algorithm is presented for continuous rotation and zoom, free from the disturbing aliasing artifacts introduced by traditional methods. Applications include smooth animation. No matrix multiplication of pixel coordinates is executed. Instead row and column parallel operations which resemble local digital filters are used. This suggests real time implementation with simple hardware. Anti-aliasing is inherent in the algorithm which operates solely on pixel data, not the underlying geometric structures whose images the pixels may depict. Zoom magnification is achieved without replicating pixels and is easily attained for any rational scale factor including but not restricted to the integer values which most existing commercial raster graphics systems use. The algorithm is based on a digitized code for lines on rasters, generalized to an interpolation scheme capable of executing all linear geometric transformations. Samples of images which have been rotated and zoomed by a software implementation of the algorithm are presented.