A subjective judgment study of polygon based curved surface imagery

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Abstract
In the past computer graphics efforts, several researchers have demonstrated that polygon models can be used to produce images of curved surfaces that appear to be smooth and accurate. However, the authors know of no attempt to appraise such imagery by using multiple human observation ratings. The effectiveness of curved surface imagery generated from polygon models was investigated in a judgment study. Research subjects evaluated sphere model imagery derived from several polygon densities and shading procedures including flat shading, shade interpolation (Gouraud) and normal interpolation (Phong). Results of the evaluations indicated that little was gained by reducing the average polygon areas below approximately 110 pixels per polygon for spheres of 95 pixel radii displayed on a 512 x 512 resolution monitor. Evaluations for both shade and normal interpolution placed polygon image quality reasonably close to an “ideal” image. Although the evaluations indicated that normal interpolation was slightly superior to the shade interpolation, shade interpolation required significantly less computation. Most significantly, results from this study provide strong support for the notion that polygons can be used effectively to produce smooth shaded imagery of curved surface models.

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