A graphics processing pipeline 1 includes a rasteriser 3 that tests patches representing respective different regions of a render output against the edges of primitives 2 to determine if the primitive at least partially covers the patch and an early depth test stage 4 that performs early depth tests for primitives in respect of patches of the render output that the primitive has been found by the rasteriser at least partially to cover, by using depth test information 5 associated with a patch indicating the number and distribution of different depth value regions associated with the patch to determine the depth value region or regions associated with the patch that the primitive should be depth tested against, and then performing a depth test or tests for the primitive in respect of the respective determined depth value region or regions associated with the patch.