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PTM's (Polynomial Texture Maps) Overview | Light Space | Image Enhancement | Viewing a PTM | Building a PTM Overview Polynomial Texture Maps (PTMs) are made from information derived from multiple digital photographs of a subject shot from a stationary camera position. In each photograph, light is projected from a different direction. This process produces a series of images of the same subject with different highlights and shadows. After the light has been projected from a representative sample of directions, all the lighting information from the images is mathematically synthesized using a method developed by Tom Malzbender and Dan Gelb at Hewlett Packard Labs. Their SIGGRAPH 2001 paper, 'Polynomial Texture Maps', describing PTMs and their mathematical foundation is available from the HP Labs website. (Download HP Labs SIGGRAPH 2001 'Polynomial Texture Maps' paper 4.9 MG ) The resulting synthesized file resembles a single 2D photographic image. Unlike a typical photograph, information derived from the 3D shape of the image's subject describes how light will reflect off the image. When the image is opened in PTM viewing software, each constituent pixel is able to reflect the software's interactive 'virtual' light from any position selected by the user. This changing interplay of light and shadow in the image is used by the human perceptual system to discloses fine details of the subject's 3D surface form. The inclusion of empirically captured reflection information along with each pixel's red, green, and blue color information enables PTMs to document 3D shape information and is the source of PTM's documentary power. Each pixel, representing an area on the subject's 3D surface, 'knows' the 3D direction that is perpendicular to that location on the surface. As the shape of the source object changes, the direction that is perpendicular to the surface also changes. Mathematically, the direction that is perpendicular to the surface at any given location is represented by a vector called a 'normal'.  In 3D virtual reality representations, normals are used by lighting models to calculate how light rays will reflect off the surface of virtual 3D geometry.  The normal information present in PTMs allows them to use similar 3D lighting techniques. The image below shows the reflection information captured in the PTM. 
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