Quadratic Shading and its Hardware Implementation

Rendering systems often represent curved surfaces as a mesh of planar polygons that are shaded to restore a smooth appearance. Gouraud shading uses linear color interpolation and its hardware implementation is relatively easy, but it handles specular highlights incorrectly and introduces annoying artifacts called Mach banding over the edges of the polygon mesh. In software rendering Phong shading has been more popular, because it can realistically handle specular materials. Since it requires the rendering equation to be evaluated for each pixel, its hardware support poses problems. This paper presents a nonlinear, i.e. quadratic interpolation scheme which is in between Gouraud shading and Phong shading. It can also be implemented in hardware as Gouraud shading but its shading quality is comparable with that of the Phong shading. The software simulation and the VHDL description of the shading hardware are also presented.