Problem with Interpolated Shading
There are several more shading models that intermediate in complication among Gouraud and Phong shading, linking the liner interpolation of the dot products utilized in the illumination models. Since in Phong shading, the illumination model is estimated at each pixel, although the interpolated dot products are utilized to ignore the expense of calculating and normalizing any of the direction vectors. Such model can generate more satisfactory effects than Gouraud shading when utilized along with specular-reflection illumination models, as the specular term is computed separately and has power-law, quite than linear, falloff. However in Gouraud shading, highlights are missed if they do not fall at a vertex, as no intensity value calculated for a set of interpolated dot products can exceed those calculated for the set of dot products at either end of the span.
There are several problems common to all these interpolated-shading models, some of that we listed this time. Polygonal silhouette: No matter how excellent an approximation an interpolated shading model gives to the real shading of a curved surface, the silhouette edge of the mesh is now clearly polygonal. We can enhance this situation by breaking the surface in a superior number of smaller polygons, although at a corresponding raise in expense.