Design of a hyperspectral imaging gonioradiometer for appearance characterization

Optical scatter properties of surfaces can be fully described by the aid of the bidirectional scatter distribution function (BSDF). In recent years, many measuring instruments have been reported that measure the BSDF of flat, spatially uniform surfaces. In this paper, an instrument is presented that allows for the determination of the spectral, spatially variant BSDF of non-flat surfaces. To this end, an existing BSDF measurement system was adapted by incorporation of a snapshot hyperspectral camera. The hyperspectral imaging system enables detailed spectral reflectance data collection for each pixel in the acquired image, paving the way to characterize samples with spatially variant reflectance properties. Moreover, since the hyperspectral system uses a plenoptic acquisition method, measurements can be performed on non-flat surfaces. The main characteristics of the refurbished instrument are discussed, considering challenges such as zooming and focusing on three-dimensional objects. Finally, some example measurements are presented to illustrate the capabilities of the instrument.