Evaluating an image-based bidirectional reflectance distribution function measurement setup

Abstract

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.

Bidirectional Reflectance Measurement and Reflection Model Fitting of Complex Materials Using an Image-Based Measurement Setup

“…It records the spectral radiance factor in the range of 390 nm-730 nm at 10-nm intervals at anormal incident (θ i ) and reflection (θ r ) angles in the range of [+80 • ,−80 • ] at 5 • intervals. Please refer to Appendix B in [14] for more details about the GCMS instrument. .…”

“…Figure 3 shows the setup in a vector plane. Our measurement setup was well explained in [14,[23][24][25], which can be referred to for more details. As discussed in [27], the captured image records the radiance (L r (θ i , θ r )) exited from the sample surface in digital values for each camera sensor.…”

“…However, they are less accurate when compared with slow and expensive techniques similar to the ones used for standardization in metrology. Sole et al [14] used and evaluated such a measurement setup by measuring fairly diffuse flexible packaging paper samples. The measurements obtained can be used to fit a reflection model (BRDF for an opaque homogeneous material), which will describe the material reflectance properties mathematically for computer graphics rendering or simulating visual appearance attributes.…”

“…In the situation where we use the measurement setup (used in [14]), a greater number of illumination directions (θ L ) would result in a higher number of incident and viewing direction combinations, thus giving a dense sampling and possibly a better estimation of the material BRDF. Measuring the samples at a number of θ L directions, however, adds to the measurement setup complexity.…”

“…In this paper, we investigate the suitability of the image-based measurement setup used in [23][24][25] to measure such complex materials and model them using well-established reflection models. This setup is well explained in [14,[23][24][25], and we would request the reader to refer to these articles for more details. We use the terminology 'our measurement setup' when referring to this image-based measurement setup.…”