Texture compression of light maps using smooth profile functions

Light maps have long been a popular technique for visually rich real-time rendering in games. They typically contain smooth color gradients which current low bit rate texture compression techniques, such as DXT1 and ETC2, do not handle well. The application writer must therefore choose between doubling the bit rate by choosing a codec such as BC7, or accept the compression artifacts, neither of which is desirable. The situation is aggravated by the recent popularity of radiosity normal maps, where three light maps plus a normal map are used for each surface. We present a new texture compression algorithm targeting smoothly varying textures, such as the light maps used in radiosity normal mapping. On high-resolution light map data from real games, the proposed method shows quality improvements of 0.7 dB in PSNR over ETC2, and 2.8 dB over DXT1, for the same bit rate. As a side effect, our codec can also compress many standard images (not light maps) with better quality than DXT1/ETC2.