mipmapping
the most popular method of antialiasing for textures is called mipmapping[1354]. it is implemented in some form on even the most modest graphics accelerators now produced. “Mip” stands for a multum in parvo, Latin for “many things in a small place”—a good name for a process in which the original texture is filtered down repeatedly into smaller images.
when the mipmapping minization filter is used, the original texture is augmented with a set of smaller versions of the texture before the actual rendering takes place. the texture (level zero) is downsampled to a quarter of the original area, with each new texel value often computed as the average of four neighbor texels in the original texture. the new, level-one texture is sometimes called a subtexture of the original texture. the reduction is performed recursively until one or both of the dimensions of the texture equals on texel. this process is illustrated in figure 6.14. the set of images as a whole is often called a mipmap chain.
Two important elements in forming high-quality mipmaps are good filtering and gamma correction. The common way to form a mipmap level is to take each 2×2 set of texels and average them to get the mip texel value.
Figure 6.14. A mipmap is formed by taking the original image (level 0), at the base of the pyramid, and averaging each 2 × 2 area into a texel value on the next level up. The vertical axis is the third texture coordinate, d. In this figure, d is not linear; it is a measure of which two texture levels a sample uses for interpolation.