A texturing system for use in a three-dimensional imaging system comprises a memory (22) for storing mip-map data for use in texturing an image. A controller (24) retrieves from the memory the mip-map data required and this data is stored in a cache (30). A lower-level mip-map generator (36) generates portions of the mip-map which is next below, in the hierarchical series, the mip-map of which portions are held in the cache. A trilinear interpolator (34) interpolates one output texel from input texels from the two mip-map levels. The texture data is represented by compressed codes. The lower-level mip-map generator (36) interpolates on the compressed code values.