Suitability of goniospectrophotometric space curves as appearance fingerprints

Goniospectrophotometric space curves were obtained by summation of spatially under-sampled bidirectional reflectance distribution function over all directions and repeating this for all wavelengths in the visible spectral region. This gives a 3D goniospectrophotometric curve called an xDNA graph. Systematic analysis applying 19 measurement geometries confirms existence of characteristic shapes of the graph for all optically similar samples. This enables distinguishing between differently rough samples, an interference effect on various transparent layers, and selective spectral absorption of light in differently thick pigmented coatings. Therefore, the considered goniospectrophotometric space curves could serve as an appearance fingerprint of such samples.