The aliasing problem in computer-generated shaded images

Abstract

Certain defects, such as jagged edges and disappearing detail, have long been an annoyance in digitally generated shaded images. Although increasing the resolution or defocusing the display can attenuate them, an understanding of these defects leads to more effective methods. This paper explains the observed defects in terms of the aliasing phenomenon inherent in sampled signals and discusses prefiltering as a recognized cure. A method for evaluating filters is presented, the application of prefiltering to hidden-surface algorithms is discussed, and an implementation of a filtering tiler is shown accompanied by examples of its effectiveness.

References

1. 1 Bui Tuong Phong. Illumination for computer-generated images. UTEC-CSc-73-129, Dept. Comptr. Sci., U. of Utah, Salt Lake City, Utah, July 1973. Abridged in Comm. ACM 18, 6 (June 1975), 311-317.
2. 2 Crow, F.C. The aliasing problem in computer-synthesized shaded images. UTEC-CSc-76-015, Dept. Comptr. Sci., U. of Utah, Salt Lake City, Utah, March 1976.
3. 3 Freeman, H. Computer processing of line-drawing images. Computing Surveys 6, 1 (March 1974), 57-97.
4. 4 Gouraud, H. Computer display of curved surfaces. UTEC-CSc- 71-113, Comptr. Sci., U. of Utah, June 1971. Abridged in IEEE Trans. Comptrs. C-20 (June 1971).
5. 5 Hunt, R.W.G., The Reproduction of Colour in Photography, Printing and Television. Fountain Press, England, 3rd Ed., 1975.
6. 6 Newell, M.G., Newell, R.G., and Sancha, T.L. A solution to the hidden-surface problem. Proc. ACM 1972 Annual Conf., Boston, Mass., Vol. I, pp. 443-450.
7. 7 Oppenheim, A.V., and Schafer, R.W. Digital Signal Processing. Prentice-Hall, Englewood Cliffs, N.J., 1975.
8. 8 Stockham, T.G. Jr., High-speed convolution and correlation. Proc. AFIPS 1966 SJCC, Vol. 28, AFIPS Press, Montvale, N.J., pp. 229-233.
9. 9 Sutherland, I.E., Sproull, R.F., and Schumaker, R.G. A characterization of ten hidden-surface algorithms. Computing Surveys 6, 1 (March 1974), 1-55.
10. 10 Zworykin, V.K., and Morton, G.A. Television. Wiley, New York, 2nd Ed., 1954.

Index Terms

• Computing methodologies

  • Computer graphics

    • Image manipulation