An image based multi-angle method for estimating reflection geometries of flexible objects

Abstract

Gonio-spectrometers and multi-angle spectrophotometers are successfully used for performing multi-angle measurements of non-diffuse materials like metallic inks and paints used in the print and packaging industry and car paint industry. Using a gonio-spectrometer to measure the amount of light reflected at different incident and reflection angles is a time consuming and an expensive process and is mainly performed in laboratories for research purposes. In order to perform multi-angle planar measurements, at relatively cheaper and faster way, we use a geometrical method which can be used with an image based measurement setup to measure such materials. The image based measurement setup help record the light reflected from the sample, in the digital pixel array sensor. The geometrical method estimates the incident (i) and reflection (r) angles at a given point (P) on the sample surface. It also maps the pixel positions on the camera sensor array to the corresponding point (P) on the sample surface. This information can therefore be used to understand the amount of light incident and reflected from a given point (P) on the sample surface and record it accordingly. The proposed measurement setup can be used in, for example packaging industry, to perform online gonio-metric measurements during material reproduction process and estimate the incident and reflection angles of homogeneous flexible object materials when measuring light incident and reflected from the sample at different angles. The results obtained show that the geometrical method corrects for the geometrical distortions and estimate the incident (i) and reflection (r) angles successfully.