Anti-aliasing computer generated graphics by alpha testing each sampling point of fragment individually

When an alpha test is performed as part of the rendering process in a multisampled graphics processing pipeline, rather than taking the single alpha value initially defined for each fragment 80, 81, 82, 83, an individual alpha value is generated in respect of each of covered sampling position that the fragment in question is being used to render. The individual alpha values estimated for each sample position are then individually compared with a threshold alpha value defined for the alpha test, and the result of this alpha test comparison is used to decide either keep or discard the sample position from further processing. Claims are also included specifying that an individual parameter value rather than merely an alpha value may be generated for a sampling point, and subsequently used in processing in relation to that point.