CMSC 435 Autumn 1997  Introduction to Interactive Graphics
Smooth Shading vs. Faceted Shading
Faceted Shading:
 1 color per polygon
 produces "unsmooth" objects
 direct rendering of the geometry
 fast
Smooth Shading:
 assumes object is really a curved surface,
approximated by a collection of polygons.
 more realistic rendering
 slower
 Two Types: Gouraud and Phong
Gouraud Smooth Shading (1971):
 Calculate Average vertex normal
 Perform illumination calculation to get vertex
colors
 Interpolate vertex colors accross the face.
 Suffers from Mach banding :
Whenever the slope of the light intensity curve changes
abruptly,
the surface appears brighter (inflection is
concave) or darker (convex)
 May miss highlights within a face.
Phong Smooth Shading (1973):
 Calculate Average vertex normal
 Interpolate vertex normals accross the face.
 Perform illumination calculation at each pixel
 More accurate highlights
 Fewer Mach Band effects
 Why do they occur?
Comparison of Shading Types



Facted Shading 
Phong Smooth Shading 
Phong Smooth Shading with Volumetric Steam 
David S. Ebert
Sun Nov 16 11:19:09 EST 1997