20.6 Gloss Maps 923
are (1, 1/2, 1/2) and (1/2, 1, 1/2), respectively. At a pixel midway between the ver-
tices, the interpolated RGB value is (3/4, 3/4, 1/2), so the uncompressed vector is
2(3/4, 3/4, 1/2) − (1, 1, 1) = (1/2, 1/2, 0), which is not unit length.
A fix to this problem is to use what is called a normalization cube map. Cube maps
are discussed in ...