Automated three-axis gonioreflectometer for computer graphics applications

Abstract

We describe an automated three-axis BRDF measurement instrument that can help increase the physical realism of computer graphics images by providing light scattering data for the surfaces within a synthetic scene that is to be rendered. To our knowledge, the instrument is unique in combining wide angular coverage (beyond 85° from the surface normal), dense sampling of the visible wavelength spectrum (1024 samples), and rapid operation (less than ten hours for complete measurement of an isotropic sample). The gonioreflectometer employs a broadband light source and a detector with a diffraction grating and linear diode array. Validation was achieved by comparisons against reference surfaces and other instruments. The accuracy and spectral and angular ranges of the BRDFs are appropriate for computer graphics imagery, while reciprocity and energy conservation are preserved. Measured BRDFs on rough aluminum, metallic silver automotive paint, and a glossy yellow paint are reported, and an example rendered automotive image is included.

Rapid BRDF Measurement Using an Ellipsoidal Mirror and a Projector

“…Li, et al 7) have proposed a three-axis instrument. However, because the angle needs to be altered mechanically, the measurement of dense BRDFs takes a long time.…”

“…This means that it is impractical to measure dense BRDFs using a gonioreflectometer. In fact, Li, et al 7) reported that the real measuring time becomes about 9-10 hours even if the number of angular configurations is 10…”

Aesthetics and Gloss of Ground Surfaces: A Review on Measurement and Generation

“…The challenges lie within having a high angular resolution, dense sampling of the visible wavelength spectrum, and rapid operation as measurements can take hours [27]. Researchers often rely on self-built gonioreflectometers or customized optical systems.…”

“…BRDF is measured with a gonioreflectometer, which consists of light source and detector moveable in relation to the sample surface [27]. The challenges lie within having a high angular resolution, dense sampling of the visible wavelength spectrum, and rapid operation as measurements can take hours [27].…”

Principles of Appearance Acquisition and Representation

“…In this case, the function being measured has only three angular dimensions, so one requires only three degrees of freedom in the acquisition system. In the gonioreflectometer recently built at Cornell [LFTW06], this is accomplished by having two degrees of freedom in the orientation of the planar sample and one additional degree of freedom in the angular position of the source. Using this system, one can acquire 31 spectral samples per camera/source position (roughly 10nm increments over the visible spectrum), and capturing 1000 angular samples (which is a very sparse covering of the 3D angular domain) takes approximately 10 hours.…”