The quantification of material appearance is important in product design. In particular, the sparkle impression of metallic paint used mainly for automobiles varies with the observation angle. Although several evaluation methods and multi-angle measurement devices have been proposed for the impression, it is necessary to add more light sources or cameras to the devices to increase the number of evaluation angles. The present study constructed a device that evaluates the multi-angle sparkle impression in one shot and developed a method for quantifying the impression. The device comprises a line spectral camera, light source, and motorized rotation stage. The quantification method is based on spatial frequency characteristics. It was confirmed that the evaluation value obtained from the image recorded by the constructed device correlates closely with a subjective score. Furthermore, the evaluation value is significantly correlated with that obtained using a commercially available evaluation device.
The sparkle impression is an important factor of appearance quality. The impression is generated by reflection from a material surface that contains metallic or pearl pigments. Although several methods of evaluating the impression have been proposed, there is insufficient correlation between the results of these methods and subjective evaluation because the impression depends on the observation distance. The present study developed a method of evaluating the sparkle impression considering the observation distance. To this end, a subjective evaluation experiment was performed for different observation distances and a measurement system comprising a spectral camera and lighting device was constructed. The evaluation model was proposed on the basis of the spatial frequency characteristics of the recorded image and human visual characteristics. The contribution ratio between subjective evaluation scores and evaluation values was high.