Abstract: An apparatus generates lighting modulation factors for samples in a volume rendering pipeline. The apparatus includes a first arithmetic logic unit squaring a gradient magnitude vector of a sample to produce a squared gradient magnitude. A second arithmetic logic unit produces a gradient magnitude from the squared gradient magnitude. A shift register, connected to the first arithmetic logic unit, truncates a predetermined number of high bits of the squared gradient magnitude. A gradient magnitude modulation register stores modulation parameters. A first multiplexer, connected to the second arithmetic logic unit and the shift register, selects the truncated squared gradient magnitude as an index if an index source signal is true, and the gradient magnitude if the index source signal is false, and a memory table is indexes by the index to produce modulated opacity, emissive, diffuse and specular modulation factors.