Abstract
The bidirectional reflectance distribution function (BRDF) data are essential for analyzing and modeling the material appearance of anisotropic surfaces. In order to acquire four-dimensional BRDF on the anisotropic material surfaces, a four-axis gonioreflectometer was designed and implemented. The instrument consists of a collimated, broadband light source, a four-axis rotation mechanism, a spectroradiometer, and a control system. The instrument is able to carry out spectral BRDF measurements over most of the incident and reflection hemispheres and the entire visible spectrum. One thousand twenty-four samples are obtained over the spectral range of 380 to 760 nm. The angular resolution of the BRDF measurement is <0.1 deg with good repeatability. A relative calibration method was adopted to obtain the absolute values of BRDFs. Various scanning schemes can be carried out by the instrument to scan the designated angular domains, enabling the instrument to capture material appearance with strong, distinctive anisotropic highlights and translucency. The obtained BRDF data of a textile sample demonstrate the instrument capability of capturing complex light scattering behaviors, including off-specular reflection peaks, off-plane reflection peaks, and backscattering. The designers of novel material appearance and computer graphics community will benefit from this work.
Highlights
Appearance capture techniques provide quantitative, detailed representations of material appearance to help us understand and simulate the visual world around us.[1]
The bidirectional reflectance distribution function (BRDF) is the most commonly used representation of material appearance, which is defined as the ratio of the radiance dLr reflected from a surface in the direction to the irradiance dEi onto the surface from the direction:[2] f ðθ ; φ ; θ ; φ Þ 1⁄4 dL dðEθ ;ðφθ ;; φθ ;Þφ Þ ; EQ-TARGET;temp:intralink-;e001;63;277 r i ir r ri ir r ii i where θi and φi are the zenith and azimuthal angles of the irradiance and θr and φr are the zenith and azimuthal angles of the reflected radiance
We present a spectral BRDF measurement instrument
Summary
Appearance capture techniques provide quantitative, detailed representations of material appearance to help us understand and simulate the visual world around us.[1]. Another example of anisotropic material is metamaterial with nanometric scale structures. Since the direction and the wavelength of the reflected light from a metamaterial can be controlled by the To meet these demands, a four-axis spectral gonioreflectometer is proposed. Compared with the other appearance measurement instruments, the proposed instrument prevails in its broadband capability, large angular range, compactness, and extensibility
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