How is color derived out of the volume data?
Color is derived from a 4,096 entry color lookup table: 8 bits for Red, 8 bits for Green, 8 bits for Blue, and 12 bits for high precision Alpha (opacity), totaling 36 bits of color. Samples are created by interpolating voxel values. Each sample has a value and a gradient representing a surface normal. The sample value is used to lookup RGB and Alpha values from the lookup table to obtain the emissive color. The gradient associated with the sample value is used in a Phong illumination algorithm to obtain diffuse and specular color values. Using two reflectance maps, specular and diffuse illumination is implemented at each sampled point.
