1. A graphics system comprising: a graphics processor configured to receive graphics primitives and to perform rendering operations on the graphics primitives to obtain a plurality of samples that represent an image, wherein the rendering operations are performed according to a plurality of screen-space regions, wherein graphics primitives that fall within a first of the regions are rendered with a different density of samples in screen space than graphics primitives that fall within a second of the regions; a sample buffer coupled to said graphics processor for storing the plurality of samples; and a sample-to-pixel calculation unit configured to access the samples from the sample buffer and to filter the samples in order to form output pixels.