Abstract: Object surface with material (lighting and texture) can be used to enhance the perception of volume rendering.In this paper, we introduce a 2D sphere illumination map, which is computed offline and used in the run time to simplify GPU shading computation to texture lookups.Color of the corresponding point in the sphere map is indexed by the normalized normal vector of the object surface, thus assigning material to the surface.This method can be simply applied to GPU-based 3D texture ray-casting algorithm.The results show the implementation permits both visual effect enhancement and efficiency improvement.