The role of rendering in the competence project in measurement science for optical reflection and scattering

ASTM gloss measurement standards are linked to the visual evaluation of gloss. Rendering is a potentially important tool in developing such standards or could become a procedure cited in new gloss standards. The work described in Sec. 4.2.3 is a first step along this line. Rendering materials under an ASTM standard procedure will enable the systematic study of the variation of the appearance of standard materials with distance between object and viewer or degree of illumination. Moreover this work shows how comparisons can be made between different rendering programs so that a computer graphic based gloss standard can be defined independently of the program used. We also note that programs rendering a set of objects with defined gloss standards can be compared, thus giving rise to a possible standard for rendering programs.

An important outcome of our work has been the demonstration that satisfactory rendering of many colored objects can be done with just a few measurements. This was seen in the rendering of metallic painted shells using iBRDF.

The BRDF has played an essential role in our study of appearance but progress in capturing complex visual effects will have to go beyond this function. The glittering micro-appearance of metallic paint so evident when one approaches a newer automobile is an effect that involves scales that are too small to be described by BRDF and depends on human binocular vision as well. Image texture is an extremely important attribute and it too falls outside the range of BRDF description. We have also neglected the effects of paint application in our modeling. Nevertheless, the rapid developments in computer graphics--where the turn around time between theoretical formulation and practical application is so short--make significant progress on these problems in the near future an exciting and likely possibility.

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Acknowledgments

We would like to thank Dr. Egon Marx and Dr. Theodore Vorburger of the Manufacturing Engineering Laboratory for their work on modeling and surface topography measurements of the coated epoxy tiles. We would also like to thank Peter Walker for his work on many of the BRDF tools and the BRDF visualization images. Finally, the authors would like to acknowledge and thank Maria Nadal of the Optical Technology Division of the Physics Laboratory for performing the BRDF measurements and for her cooperation and collaboration in creating a measurement protocol for rendering applications.

Accepted: May 15, 2002

6. References

(1.) M. E. McKnight, J. W. Martin, M. Galler, F. Y. Hunt, R. R. Lipman, T. V. Vorburger, and A. E. Thompson, Report of workshop on advanced methods and models for appearance of coatings and coated object. J. Res. Natl. Inst. Stand. Technol. 102(4), 489 (1997).