Using multiple illumination maps
Some applications may require a different illumination map for different kinds of materials.
Up to three illumination maps can be authored for each vignette. The illumination map for a render operation is selected with the illum= and or gloss= commands.
Default selection If neither illum= nor gloss= are specified, the renderer will use the first authored illumination map (typically map A, aka the 'Flat' illumination map).
Automatic selection with gloss= If illum= is not specified or is set to -1, the renderer compares the specified gloss= value with the gloss values associated with each illumination map in the vignette, and choose the illumination map whose gloss value is closest to the specified gloss= .
Explicit selection with illum= If illum= is specified and set to 0, 1, or 2, the renderer will use the corresponding illumination map; gloss= is ignored for the purpose of selecting the illumination map.
If the vignette contains only one illumination map, the renderer will use that map and ignore the illum= and gloss= commands.