Gourand shading OR Intensity interpolation scheme
Now there polygon is rendered through linearly interpolating intensity values across the surface. Intensity values for all polygons are matched along with the values of adjacent polygons beside the general edges, hence eliminating the intensity discontinuities which can arise in flat shading.
Computations to be performed for all polygon surfaces rendered along with Gourand shading as:
1. Find out average unit normal vector at each polygon vertex.
2. Apply illumination model to all vertex to compute the vertex intensity.
3. Linearly interpolate the vertex intensities over the surface of the polygon.