CMSC 435 Autumn 1998 --- Introduction to Interactive Graphics
Smooth Shading vs. Faceted Shading
Faceted Shading:
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1 color per polygon
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produces "unsmooth" objects
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direct rendering of the geometry
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fast
Smooth Shading:
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assumes object is really a curved surface, approximated by
a collection of polygons.
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more realistic rendering
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slower
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Two Types: Gouraud and Phong
Gouraud Smooth Shading (1971):
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Calculate Average vertex normal
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Perform illumination calculation to get vertex colors
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Interpolate vertex colors accross the face.
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Suffers from Mach banding :
Whenever the slope of the light intensity curve changes
abruptly,
the surface appears brighter (inflection is concave)
or darker (convex)
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May miss highlights within a face.
Phong Smooth Shading (1973):
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Calculate Average vertex normal
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Interpolate vertex normals accross the face.
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Perform illumination calculation at each pixel
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More accurate highlights
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Fewer Mach Band effects
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Why do they occur?
Comparison of Shading Types
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|
|
Facted Shading |
Phong Smooth Shading |
Phong Smooth Shading
with Volumetric Steam |
David S. Ebert
November 1998