Texture mapping can be divided into two-dimensional and three-dimensional techniques. Two-dimensional techniques place a two-dimensional (flat) image onto an object using methods similar to pasting wallpaper onto an object. Three-dimensional techniques are analogous to carving the object from a block of marble.
In three-dimensional texture mapping, each point determines its color without the use of an intermediate map shape (Peachey, 1985; Perlin, 1985). We use the (x,y,z) coordinate to compute the color directly. Its equivalent to carving an object out of a solid substance.