Low-frequency correlations (1/f^α type) in paint application of metallic colors

Abstract

We examine trial-to-trial variability of color coordinates in automotive coatings containing effect pigments, which are considered a reference paradigm for engineering angle-dependent color effects. We report the existence of correlations that show 1/f - Fourier spectra at low frequencies in all color coordinates. The scaling exponent was lower at near-specular conditions for lightness variations, suggesting a contribution from the deposition of metal flakes in metallic colors. However, the exponent was lower near the specular for blue-yellow variations, suggesting a contribution from chemical pigments in solid colors. These results were independent of the illuminant spectra. The methods employed are useful in the evaluation of industrial color matching among assembly parts.

Classification of batch processes in automotive metallic coatings using principal component analysis similarity factors from reflectance spectra

“…Finally, PCA methods do not necessarily preserve the temporal order of reflectance spectra within and between color batches in comparison to time series analysis of color coordinates [17], and thus, they are not very sensitive to the start and end of atypical conditions during industrial painting. This could be especially useful in the search for specific spectral patterns within large historical reflectance databases where the start and end of abnormal painting conditions are not known a priori.…”

“…Reflectance spectra are mapped to color coordinates [4,9,10] and a set of pass/fail color tolerances or threshold values are usually defined for agreement with visual assessment at all selected viewing angles [4,9,13,16]. However, color tolerances are difficult to define near the specular reflection [9,16] and often ignore trial-to-trial correlations of color coordinates from deposition of effect pigments and painting conditions [17].…”

Efficient frequency conversion based on local optimization theory

“…For this purpose, it will be assumed that both the two TWM processes are phase-matched, and that the desired modulation of the coupling coefficient κ ij has been achieved. We considered the two-process TWM in equation (1) where:…”

“…Mid-infrared lasers in the 3-5 μm wavelength region have many applications, such as spectrum, military countermeasures and remote monitors of the special environment, and so on [1,2]. In recent years, the technique of STIRAP to achieve efficient and robust frequency conversion has been the subject of many theoretical and experimental studies [3][4][5][6][7][8][9][10][11].…”