A gonioreflectometer for measuring the bidirectional reflectance of material for use in illumination computation.

Master's thesis, Cornell University, 1996.

This thesis presents the detailed design and measurement procedures of an automated three-axis gonioreflectometer for measuring the bidirectional reflectance distribution function (BRDF) of an isotropic material for use in computer graphics rendering. The working gonioreflectometer is a modification of a partially completed instr ument donated by Kodak to the Light Measurement Laboratory of the Cornell Program of Computer Graphics. The gonioreflectometer consists of a broad band light source that emits parallel rays in the visible wavelength range. The light source revolves around the test sample which itself has two degrees of freedom of rotation. The detector is stationary and views the test sample via a folding mirror. The detector consists of external focusing optics, a diffraction grating spectrograph, and a diode-array sensor. The system has a high dynamic range and can measure the reflection at high grazing angles (up to 86°). Both absolute calibration by measuring the direct irradiance, and relative calibration by using a reference sample, can be used for converting measurements to BRDF values. BRDFs of three different samples, a white PTFE sample (Spectralon), a latex blue paint, and a matte-finished steel plate (Q-Panel R-46), were measured with the gonioreflectometer. The results are presented along with close comparisons to data published by other facilities. Specular reflectance and directional-hemispherical reflectance measured with the instrument were cross-checked to measurements made with an Optronic Spectroradiometer (OL-750).

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