CMSC 635: Advanced Computer Graphics

Smooth Shading vs. Faceted Shading

Spring 1999

Computer Science and Electrical Engineering Department
University of Maryland, Baltimore County

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