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Spatially resolved measurements of diffuse reflectance.


Diffuse reflectance measurements in sphere geometries are usually performed using a single photodetector. However measurements of graininess require also spatial resolution, thus they are performed using a radiometric camera attached to the integrating sphere. The usually applied measurement geometry is d:0°. When performing such measurements on glossy samples, the phenomenon of gloss exclusion can directly be observed: a dark area corresponding to the specular excluded solid angle. METAS and PTB have performed a systematic study on a set of samples having different values of gloss, lightness, and colour, using two different measurement setups. It was found that the size of the dark area could be calculated using geometric relations of the measurement setup. Furthermore, the reflectance factor of the dark area, compared to its surround can be correlated with the gloss value of the sample: the higher the gloss of the sample, the greater the difference between the dark area and its surround.

Blattner, P.; METAS, Bern, SWITZERLAND
Pastuschek, Marcel; 4.5, Angewandte Radiometrie, PTB-Braunschweig
Schirmacher, Alfred; 4.5, Angewandte Radiometrie, PTB-Braunschweig