Polynomial Texture Maps (PTMs) are a simple representation for images of functions instead of just images of color values. In an conventional image, each pixel contains static red, green, blue values. In a PTM, each pixel contains a simple function that specifies the red, green, blue, values of that pixel as a function of two independent parameters, lu and lv.
Typically, PTMs are used for displaying the appearance of an object under varying lighting direction, and lu,lv specify the direction of a point light source. However, other applications are possible, such as controlling focus of a scene. PTMs can be used as light-dependent texture maps for 3D rendering, but typically are just viewed as ‘adjustable images’.
PTMs are typically produced with a digital camera by photographing an object multiple times with lighting direction varying between images. Even a low-end digital camera provides enough resolution to produce good PTMs, and almost any light source can be used such as a light bulb, >LED or flash.