1. A texture filtering apparatus comprising: a first generating unit configured to generate first texture data having a size designated by a user or satisfying a condition designated by the user by using not less than second texture data acquired under different conditions or generated under different conditions; a second generating unit configured to generate texture data for filtering used for filtering by using the first texture data; and a filtering unit configured to perform filtering on the first texture data by using a designated filtering condition and the texture data for filtering, the first generating unit further including an input device to input an arbitrary size or an arbitrary condition for a texture to be generated a texture generation unit to implement texture generation with the arbitrary size by pattern matching or texture generation under the arbitrary condition by linear interpolation, an expression unit to express the first texture data by using an index image of a plurality of index images and a codebook of a plurality of codebooks, an optimization unit to optimize the codebook by vector quantization processing if a data size of the first texture data is larger than a threshold value, and a re-assigning unit to re-assign an index for each pixel of the index image.