Displays with repeating patterns of colored sub-pixels gain spatial resolution by setting individual sub-pixels rather than by setting entire pixels. This paper describes optimal filtering that produces sub-pixel values from a high-resolution input image. The optimal filtering is based on an error metric inspired by psychophysical experiments. Minimizing the error metric yields a linear system of equations, which can be expressed as a set of filters. These filters provide the same quality of font display as standard anti-aliasing at a point size 25% smaller. This optimization forms the filter design framework for Microsoft’s ClearType.