Shading Algorithms for 3-d Computer Graphics

Computer graphics deals with realistic rendering of 3-d objects. There are many rendering algorithms used. Two of the most famous algorithms are Gouraud Shading Algorithm and Phong Shading Algorithm. These algorithms handle location of light source, location of the camera, and surface reflection properties in different manners and produce different results. Their computational complexities are also very different; Phong Shading being very complex compared to Gouraud Shading. In this talk, the rendering problem is analyzed using 3-d geometry to see how location of light source, location of the observer, and the surface reflection properties play their role. The equations for the two shading algorithms is derived, the computational complexities of the algorithms are compared, and an adaptive shading scheme is presented that chooses between computationally complex Phong Shading algorithm to render the parts of a 3-d object where it is really needed. For other parts of the 3-d object, computationally simple Gouraud Shading is used. This type of adaptive shading scheme has been in existence for some time. However, the algorithms for selection between two rendering methods are not very robust. A new algorithm, developed by the author, for such selection is presented. The comparative results of existing algorithms vs.. the new algorithm are also presented.