Effects of Global Illumination Approximations on Material Appearance
Jaroslav Krivanek, James Ferwerda, Kavita Bala
Proceedings of SIGGRAPH 2010 (SIGGRAPH 2010)
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Abstract:
Rendering applications in design, manufacturing, ecommerce and
other fields are used to simulate the appearance of objects and
scenes. Fidelity with respect to appearance is often critical, and
calculating global illumination (GI) is an important contributor to
image fidelity; but it is expensive to compute. GI approximation
methods, such as virtual point light (VPL) algorithms, are efficient,
but they can induce image artifacts and distortions of object
appearance. In this paper we systematically study the perceptual
effects on image quality and material appearance of global illumination
approximations made by VPL algorithms. In a series of psychophysical
experiments we investigate the relationships between
rendering parameters, object properties and image fidelity in a VPL
renderer. Using the results of these experiments we analyze how
VPL counts and energy clamping levels affect the visibility of image
artifacts and distortions of material appearance, and show how
object geometry and material properties modulate these effects. We
find the ranges of these parameters that produce VPL renderings
that are visually equivalent to reference renderings. Further we
identify classes of shapes and materials that cannot be accurately
rendered using VPL methods with limited resources. Using these
findings we propose simple heuristics to guide visually equivalent
and efficient rendering, and present a method for correcting energy
losses in VPL renderings. This work provides a strong perceptual
foundation for a popular and efficient class of GI algorithms.
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