Abstract
This paper attempts to generalize and to unify the shading models described by Gouraud [1] and Phong [2]. The major effort in this direction is to produce a model that exhibits the following features:
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1.
It is incremental in an arbitrary scan direction across a two dimensional polygon.
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2.
The increments in the x and y directions are constant across the elementary polygon to be shaded.
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3.
It maintains continuity of the intensity I or of the normals N when traversing the edges that bound the elementary polygons.
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4.
In the case of the shading process following the projection it considers the contribution of the z coordinate.
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5.
The shading is invariant with respect to rotation.
The first three features are satisfied by the models proposed by Gouraud and Phong whereas the last two are not. It is the purpose of this paper to introduce a general model that is invariant with respect to rotation, can be applied either before or after projection and is insensitive to the presence of concave vertices.
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Bibliography
H. Gouraud, “Continuous Shading of Curved Surfaces”, IEEE Transactions on Computers, C-20(6), June 1971, pp 623–628.
Bui-Tuong Phong, “Illumination for Computer Generated Pictures”, Communications of the ACM, 18(6), June 1975, pp 311–317.
J. D. Foley and A. VanDam, “Fundamentals of Interactive Computer Graphics”.
T. Duff, “Smooth Shaded Renderings of Polyhedral Objects on Raster Displays”, Computer Graphics, Vol. 13, pp. 270–279, 1979 (Proc. SIGGRAPH 79).
J. Stoer and R. Bulirsch, “Introduction to Numerical Analysis”, Springer-Verlag, pp 210–213.
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© 1988 Springer-Verlag Berlin Heidelberg
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Sfarti, A. (1988). A General Shading Model. In: Magnenat-Thalmann, N., Thalmann, D. (eds) New Trends in Computer Graphics. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-83492-9_9
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DOI: https://doi.org/10.1007/978-3-642-83492-9_9
Publisher Name: Springer, Berlin, Heidelberg
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