Observation of visual texture of metallic and pearlescent materials

Abstract

We have investigated the visual texture properties of effect coatings. The key question addressed in this work is how the visual texture properties of effect coatings can be visually assessed in a reproducible way.We show that it is possible to define two important visual texture parameters: Diffuse Coarseness and Glint Impression. These two parameters describe the visual texture under two different illumination conditions: diffuse and directional lighting, respectively. Strict definitions of these illumination conditions were found to be crucial when discussing visual texture of effect coatings. For each of these two visual texture parameters, experiments were set up, and observation procedures were designed that standardize the observation conditions. Visual tests were performed on both visual texture parameters. We found good results in terms of observer-repeatability and observer-accuracy. Our results show that if the visual texture of effect coatings needs to be visually characterized under different illumination conditions, such as different light booths or changing weather conditions, both diffuse and directional illumination should be included separately.

Perceptual analysis of distance measures for color constancy algorithms

“…As a measure of the interobserver variability, the individual differences from the mean observer scores are computed, a procedure that is often used in studies involving visual judgements, e.g., [32,33]. For each observer, the correlation coefficient of his or her average algorithm scores (averaged over scenes and illuminants) with the algorithm scores of the average observer is computed.…”

Spectral BRDF-based determination of proper measurement geometries to characterize color shift of special effect coatings

“…The increasing popularity of these coatings demands the development of new techniques and instruments to characterize the spectral reflectance and the color as a function of the different irradiation/viewing geometrical configurations [3,[6][7][8][9][10][11][12][13][14], and for different illuminants and real light sources [15]. Full knowledge of the spectral bidirectional reflectance distribution function (BRDF) of these coatings makes it possible to infer the coating color for any geometrical configuration (irradiation and viewing directions and solid angles) as well as the spectral distribution of the irradiation [16].…”

Color representation and interpretation of special effect coatings

“…The increasing popularity of special effect coatings demands the development of new techniques and instruments to characterize their color [4][5][6][7][8][9][10][11][12][13][14][15]. Of particular relevance is to determine a reduced set of measurement geometries to completely characterize these coatings.…”