When Phong shading are at the vertices ( vertices s) of a polygon normals calculated and then the coloring of an image pixel between the vertex normals is interpolated a new standards, with which the underlying illumination model can be evaluated with this normal. The results of Phong shading are qualitatively better than those of Gouraud shading , but the mathematical calculations are more complex, since the lighting model is evaluated for each pixel. In contrast, Gouraud shading only evaluates this at the corner points and only interpolates the color value obtained. Due to the increased interpolation of the normals, faceted surfaces of a displayed object appear very soft and only the silhouette reveals that it is a coarse polygon mesh.
The Phong shading should not be confused with the Phong lighting model . The latter is a lighting model and not an interpolative shading technique . However, it is possible to combine both techniques.
- Bùi Tường Phong: Illumination for Computer Generated Pictures. Communications of the ACM 18,6 (Jun. 1975): 311-317,