6.3.3 Bump Map

From [pov:6.7.2.3]:
Instead of placing the color of the image on the shape like an image_map a bump_map perturbs the surface normal based on the color of the image at that point. The result looks like the image has been embossed into the surface. By default, a bump map uses the brightness of the actual color of the pixel.

BUMP_MAP:
    normal
    {
        bump_map
        {
            BITMAP_TYPE "bitmap.ext"
            [BUMP_MAP_MODS...]
        }
        [NORMAL_MODFIERS...]
    }

BITMAP_TYPE:
    gif | tga | iff | ppm | pgm | png | jpeg | tiff | sys

BUMP_MAP_MOD:
    map_type Type | once | interpolate Type | use_color | 
    use_colour | bump_size Value