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Polynomial Texture Map (.ptm) File Format
Malzbender, Tom; Wolters, Hans; Gelb, Dan
HPL-2001-104
Keyword(s): graphics hardware illumination; image processing; image-based rendering; reflectance and shading models; texture mapping
Abstract: Polynomial texture maps (PTM's) are an extension to conventional texture maps that allow enhanced image quality. As opposed to storing a color per pixel, these PTM's store second-order bi-quadratic polynomial coefficients per pixel. These polynomials model the changes that appear to a pixel color based on either light source position or viewing direction. For example, if Lu,Lv are the parameterized light source directions and a (subscript 0-5) the scaled and biased polynomial coefficients, a color channel intensity C are arrived at via: C=a(subscript 0)L(subscript u, superscript 2) + a(subscript 1)L(subscript v, superscript 2)+a(subscript 2)L(subscript u)L (subscript v)+a(subscript 3)L(subscript u) + a(subscript 4)L(subscript v) + a(subscript 5) This document describes the file format used for representing PTM's. PTM files are designated by the suffix .ptm. Notes: This abstract contains mathematical formula which cannot be represented here.
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