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Addressing Grazing Angle Reflections in Phong Models
| Content Provider | CiteSeerX |
|---|---|
| Author | Boll, Jannik Frisvad, Revall Conradsen, Knut Aanæs, Henrik |
| Abstract | the rendered spheres by a directional light at glancing incidence (NE hemisphere) and one at grazing incidence (SW hemisphere). Our new Phong model variant is a combination of the Phong and Blinn-Phong variants, which achieves a better fit of the measured BRDFs at grazing angles. Note that the reflectance at grazing angles is Phong-like for some materials (a) and Blinn-Phong-like for others (c). The Phong illumination model is used extensively as it is simple with few parameters. It is however often challenging to fit such a single lobed model to the bidirectional reflectance distribution func-tion (BRDF) of a real material, especially at grazing angles (Fig. 1). The fitting issues are in shortcomings of the model, in choosing er-ror function, and in initial guess sensitivity [Matusik et al. 2003]. In previous work [Ngan et al. 2005], these issues were bypassed by using two specular lobes, by ignoring very grazing angles (>80◦), and, in cases of unsatisfactory fitting quality, by manually restart-ing the fitting procedure with a different initial guess. In this work, we also fit Phong models to the BRDFs measured by Matusik et al. [2003], but we focus on the difficult grazing angles. Our result is a new Phong variant that fits better to a broader range of mate-rials, and, for this model, we address the above-mentioned fitting issues. Common Phong Model Variants. Our model is a mixture of the modified Phong model (fPr) and the modified Blinn-Phong model (fBPr). These are defined by [Akenine-Möller et al. 2008] fPr (~ωi, ~ωo) = ρd pi + ρs s+ 2 |
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| Access Restriction | Open |
| Content Type | Text |
