Total Appearance Assessment Based On Samples With Metallic Coatings

Since metallic coating is widely used as a kind of decorative material, its total appearance assessment is becoming more and more important. Color, gloss and texture are the three key components for the total appearance of metallic coatings. So far, several domestic and overseas scholars have studied some single attribute of the metallic coatings, but the link and interaction between these attributes have not yet been fully considered and so the total appearance of metallic coatings has failed to be described perfectly. In order to evaluate the total appearance of metallic coatings comprehensively and accurately in consistent with the actual visual results, further studies are necessary.In this study, on the one hand, based on the various visual assessment data and instrumental measurements under different conditions, the prediction of color appearance, gloss, texture and their relationships were investigated. On the other hand, due to the total appearance difference being caused by the angle between the splicing samples with the same metallic coating, the psychophysical experiments were carried out to determine the angle thresholds for the just perceptible and just acceptable difference of the total appearance and then the influencing factors on the angle thresholds were discussed in detail.In the evaluation experiments of the appearance attributes, the psychophysical method of magnitude estimation was adopted to assess the color appearance parameters, gloss and texture of the specially designed and custom-made 161 metallic samples. For the color appearance parameters, the color appearance model of CIECAM02 can well predict the lightness and hue of the samples, while with a relatively poor prediction for the colorfulness. The correlation between the measurements by a glossmeter and the visual gloss values depends upon the gloss levels of the test samples and their chosen measurement geometries. Based on the measurements at the incident angles of 20°?60° and 85°, respectively, a continuous and smooth model was proposed to effectively predict the visually perceptual surface gloss of metallic coatings. According to the visual evaluations of texture, the impacts of the gloss levels as well as the color regions of the samples on the visual texture were analyzed and an optimization model was established based on the measured parameters by BYK-mac with the improvement of texture prediction accuracy. In addition, the fractal dimensions from image analysis were explored to characterize the texture of metallic coatings and were further verified to be effective and practical.With the 23 representative samples carefully selected from the metallic paint sample library of a certain automotive company, the angle thresholds of just perceptible and just acceptable appearance difference were collected in both concave and convex directions at different sample placement modes. By comparing the angle thresholds under different conditions, the scaling relation between the just acceptable and just perceptible angle thresholds was deduced and also the factors influencing the total appearance were discussed, including the portrait or landscape placement mode of samples and the positive (concave) or negative (convex) direction of sample rotation. Meanwhile, linking the angle thresholds to the appearance attributes indicates that the lightness of the test sample contributes most to the just perceptible as well as the just acceptable angle thresholds between the two splicing surfaces of the sample parts painted with the same metallic coating.Finally, on the basis of summarizing the research of this thesis, the prospects of the future study were also proposed.