1. A method of generating a set of polygon vertices over a region of a three-dimensional object in a graphics processing pipeline, the method comprising: determining, from information representative of the surface relief of the region of the three-dimensional object, meta-information representative of the surface relief of the region of the three-dimensional object, wherein the meta-information comprises a plurality of values corresponding to one or more points over the region of the three-dimensional object, wherein at each of the one or more points the meta-information comprises plural values, each of the plural values representative of respective, different frequency components of a plurality of frequency components that are representative of and derived from the surface relief of the region of the three-dimensional object; determining, based on the plural values representative of the plurality of frequency components at each of one or more points over the region of the three-dimensional object, whether to generate a set of polygon vertices over the region of the three-dimensional object; generating the set of polygon vertices over the region of the three-dimensional object, when this is determined to be required, wherein the number of polygon vertices generated in the set of polygon vertices depend on the plural values representative of the plurality of frequency components at each of the one or more points over the region of the three-dimensional object; and setting the positions of one or more vertices in the set of polygon vertices based on the information representative of the surface relief of the region of the three-dimensional object.