We describe an automated three-axis gonioreflectometer, which can help increase the physical realism of computer graphics renderings by providing light scattering data for the surfaces in a scene. The gonioreflectometer performs rapid measurements of the bidirectional reflectance distribution function (BRDF) for flat, isotropic, sample surfaces over the complete visible spectrum and over most of the incident and reflection hemispheres. The instrument employs a broadband light source and a detector with a diffraction grating and linear diode array. Validation is 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 paint, and a glossy yellow paint are reported, and an example rendered automotive image is included.
We present an experimental study of the angular distribution of light scattered from several rough metallic surfaces, which cover a range of roughness conditions. The substrate materials are steel or glass; roughened by bead-blasting, grinding, or etching; and aluminum- coated. The measured surface-roughness statistics are filtered by using a composite roughness model. The raw mechanical roughnesses range from 0.21μm to 2.66μm; the high-frequency small-scale roughnesses range from 0.13μm to 0.86μm. The optical wavelength is 550nm, so that the roughness-to-wavelength ratio is of order
one. A BRDF model based on the Kirchhoff approximation is used to establish a relationship between surface-height statistics and the angular distribution of the scattered light. Angular distributions calculated with the BRDF model are fit to the measurements. The best-fit roughness statistics from the BRDF model agree closely with those measured for the high-frequency small-scale roughness component. The latter roughness component, which has the highest surface slopes, is thus the primary contributor to the angular distribution of the reflected light. We show that the Kirchhoff approximation can be applied to rough metallic surfaces that have multiple scales of roughness and near-, but not perfect, Gaussian surface-height distributions.
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.
The IR scene projector consisted of resistor array is an important device in the IR simulation technology. An enhanced version of the resistor array is currently under development. Thermal radiation characterization is necessary for the performance evaluation of the device. The resistor and its array are tested by the microscopic set of a thermal video system. The dependence of the radiation temperature on control voltage, the radiation power of the resistor, the uniformity of the radiation temperature, as well as the dynamic characteristic have been measured. An evaluation of thermal radiation characteristics of the resistor array has been provided. At the same time the effective emissivity of the resistor has been measured to obtain the true temperature distribution. It is possible to be used to improve the thermal design of this device.