PHYSICAL TEXTURE MAPS

1. The most typical example of a texture T is a 2-dimensional rectangular image: T(s,t) where s,t are texture coordinates and T(s,t) is a RGB or RGBA value called texel (for "texture element").
2. But T can be one, three or four dimensional as well: T(s), T(s,t,r) and T(s,t,r,q) respectively.
   -- NOTE: The t-coordinate defaults to 0. The r-coordinate is not used at present but defaults to 0. The q-coordinate is the normalizing coordinate, that defaults to 1.
3. In OpenGL, the texel values could be 1-, 2-, 3- or 4-component, with the following interpretation

   Number of Components	Type of Components
   1	L (Luminance)
   2	L and A (Alpha)
   3	RGB
   4	RGBA

4. How these components are used is discussed in modulating and blending textures.