Texture mapping means the mapping of a function onto a surface in 3D. The domain of the function can be one, two, or three dimensional, and it can be represented by either an array or a mathematical function. The source image (texture) is mapped onto a surface in 3D object space, which is then mapped to the destination image (screen) by the viewing projection. Texture space is labeled $(u, v)$, object space is labeled $(x_0, y_0, z_0)$, and screen space is labeled $(x, y)$. Illumination mapping is the mapping of specular or diffuse reflection. It is also known as reflection mapping or environment mapping.