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We evaluate an image-based multiangle bidirectional reflectance distribution function measurement setup by comparing it to measurements from two commercially available goniospectrophotometers. The image-based setup uses an RGB camera to perform bidirectional measurements of the sample material. We use a conversion matrix to calculate luminance from the captured data. The matrix is calculated using camera spectral sensitivities that are measured with a monochromator. Radiance factor of the sample material is measured using a commercially available tabletop goniospectrophotometer and compared to measurements made using the image-based setup in the colorimetric domain. Our measurement setup is validated by comparing the measurements performed using a goniospectrophotometer. Uncertainty and error propagation is calculated and taken into account for validation. The sample material measured is wax-based ink printed on packaging paper substrate commonly used in the print and packaging industry. Results obtained show that the image-based setup can perform bidirectional reflectance measurements with a known uncertainty. The goniospectrophotometer measurements lie within the uncertainty of the measurements performed by the image-based measurement setup. The setup can be used to perform bidirectional reflectance measurements on samples with properties similar to the samples used in this paper.

Image based measurement setups are widely used for multidirectional reflectance measurements of materials. Different reflection models are used to estimate the material reflectance.In this paper we use two commonly known simple reflection models to evaluate an image based measurement setup proposed in our previous studies. Sample material is measured at multiple incident and viewing directions using the setup. The captured data is divided into training and test set to evaluate the setup. Two reflection models are trained using the training dataset. To evaluate the measurement setup, one of the sample materials is measured at few incident and viewing directions using a light source and a Tele-Spectro-Radiometer (TSR). This measured data is then compared with the reflectance estimated by the two reflection models.Results shows that image based multi-directional reflectance measurements can be performed using measurement setup proposed in our previous work. The data captured using the setup can be used to fit different reflections models for the sample materials used in this setup.

Materials with a complex visual appearance, like goniochromatic or non-diffuse, are widely used for the packaging industry. Measuring optical properties of such materials requires a bidirectional approach, and therefore, it is difficult and time consuming to characterize such a material. We investigate the suitability of using an image-based measurement setup to measure materials with a complex visual appearance and model them using two well-established reflection models, Cook–Torrance and isotropic Ward. It was learned that the complex materials typically used in the print and packaging industry, similar to the ones used in this paper, can be measured bidirectionally using our measurement setup, but with a noticeable error. Furthermore, the performance of the reflection models used in this paper shows big errors colorimetrically, especially for the goniochromatic material measured.