Abstract
Nowadays, the automotive coating market is governed by a demand for deep and vibrant colors with effects. In this field, the requirement is very high because the color is associated with a sign of quality. In a typical collision, different parts of the vehicle may be damaged. The damaged part must be repaired, sanded and prepared before being painted. To reduce costs, the body shop must then prepare a paint with a good color matching, and thus as fast as possible. It is therefore necessary for the formulation of the repair coating to reproduce the effects, both colored and textured, from absorbent or effect pigments (aluminum particles, pearlescent materials …) from a characterization of the concerned vehicle coating. It is relatively simple to qualify the colored effects from the reflectance curves and then the CIELab coordinates. However, the description of the texturing effect generated by the distribution of effect particles at the microstructure scale is quite complex. The metrological approach of the perceptive properties is still at its beginnings. The parameters used do not necessarily correspond directly to the phenomena actually perceived by the human eye. As part of this thesis work, the mobilization of expert knowledge through various sessions of free sorting and brainstorming on coated samples made it possible to highlight really perceptive texture descriptors. These descriptors have been the subject of "objective" evaluations by experienced observers. They thus made it possible to associate a quantitative evaluation scale with each descriptor. This stage of the present thesis work allowed the establishment of ground truth data materialized by a set of reference samples representing different ordered levels of a descriptor. These ground truth data were then used to design a set of measurable physical texture descriptors that were directly correlated to perceptual scales constructed in the previous step. In the procedure developed, the human eye has been replaced by a digital camera acting as a tristimulus integrator of radiometric information. The image acquisition phase was a decisive step in the process: it was necessary to reproduce the conditions of evaluation of the properties perceived, recognized and retained during the various stages using expert human observers. It was then possible to characterize the texture phenomena by image analysis and to correlate them with the values of the previously defined mean observer.