Goniospectrophotometric space curves of diffraction gratings and their applicability as appearance fingerprints

Abstract

The bidirectional reflectance distribution functions of diffraction gratings were calculated by applying diffraction theory and transformed into goniospectrophotometric space curves. Gratings with parallel sinusoidal grooves having periods of 1-3.5 μm and amplitudes below 0.2 μm were analyzed. The obtained goniospectrophotometric space curves consist of lines with different slopes and possible interconnections. The slope of the lines is directly connected to the grating period and the length to the period and the amplitude. Such curves could be regarded as a simple appearance fingerprint of a diffraction grating. The ability of portable multiangle spectrophotometers to provide them for diffraction gratings is analyzed.

Color characterization of coatings with diffraction pigments

“…Previous experimental studies on coatings with diffraction coatings have been recently published, showing the color travel of these coatings in CIE a*,b*-diagrams [11,12]. Interestingly, theoretical simulations can be found in literature [13], giving insight in the dependence of the spectral reflectance on the period of the diffractive grating and its amplitude.…”

Angular and Spectral Bandwidth Considerations in BRDF Measurements of Interference- and Diffraction-Based Coatings

“…The spectral BRDF of goniochromatic surfaces changes in great extent for different combinations of illumination and viewing directions (geometries), and it makes their colorimetric description complex. Most of the research work on the appearance of goniochromatic surfaces has dealt with the proper methodology to describe their color by selecting adequate geometries, and to use measurements for representing such surfaces [6][7][8][9][10][11][12][13][14][15][16][17]. However , the metrological aspect of measuring the spectral BRDF and the color with real instruments, which have finite-size apertures, has not been systematically studied yet as in this work.…”

“…Since the deflection depends on the wavelength, the color at a given observation direction depends on the deflection angle with respect to the normal direction to the pigment. In coatings based on diffraction pigments, the color shift reveals very clearly when varying the aspecular angle at a constant incidence angle [2,[15][16][17]31]. An example of this color shift with the geometry is shown as a CIE a*b* diagram in Figure 2, for one of the highly goniochromatic diffraction-based special effect coating studied in Reference [15] (SpectraFlair R Silver 1500-14).…”