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Abstract:
We discuss the validation of BTF data measurements by means used for BRDF
measurements. First, we show how to apply the Helmholtz reciprocity and
isotropy for a single data set. Second, we discuss a cross-validation for BRDF
measurement data obtained from two different measurement setups, where the
measurements are not calibrated or the level of accuracy is not known. We show
the practical problems encountered and the solutions we have used to validate
physical setup for four material samples. We describe a novel coordinate system
suitable for resampling the BRDF data from one data set to another data set.
Further, we show how the perceptually uniform color space CIELab is used for
cross-comparison of BRDF data measurements, which were not calibrated.
