Phong Shading

Phong shading is based on a linear interpolation of the normal vectors from each vertex of the polygon. Just as with Gouraud shading, the normal is calculated at each vertex and used to produce an intensity. The intensity calculation will contain a term for a specular highlight. To fill the polygon, the normal vectors rather than intensities are interpolated from point to point. Using these interpolated normals, the intensities with a specular highlight are calculated at each pixel.

Computing the intensities is not as easy as it sounds since the pixel values are in image space and the normal values are from object space!

Phong Shading and Gouraud Shading Java Applet