Abstract
Sparkle and graininess are textural effects that appear as intrinsic spatial features of coatings containing goniochromatic pigments, whereas others such as mottling are undesired outcomes. In this study, we present new methods for the evaluation of sparkle, graininess and mottling of automotive coatings through images acquired with a novel gonio-hyperspectral imaging system based on light-emitting diodes with extended spectral sensitivity beyond the visible range (368–1309 nm). A novel analysis of sparkle that considered the amount of sparkling spots was used. Graininess was quantified through a novel statistical descriptor based on the energy descriptor computed from the histogram. A new index was proposed for an enhanced detection of mottling based on the analysis of striping, which was better observed and quantified in the infrared range. Spectral assessments showed a strong relationship with color and spectral reflectance for graininess and mottling. In conclusion, the results showed that these new spatial and spectral methods are a suitable, alternative and potential approach for the assessment of these textural features.
Highlights
IntroductionThe automotive sector has been responsible for the huge production and evolution of these pigments due to the need to constantly launch vehicles with impressive innovations
The appearance of objects has become more complex with the emergence of special effect pigments.The automotive sector has been responsible for the huge production and evolution of these pigments due to the need to constantly launch vehicles with impressive innovations
In order to overcome the limitations of currently existing instruments, we propose the evaluation of sparkle, graininess and mottling by means of novel parameters extracted from a gonio-hyperspectral imaging system based on light-emitting diodes (LEDs) previously applied to the colorimetric and spectral evaluation of goniochromatic coatings [35]
Summary
The automotive sector has been responsible for the huge production and evolution of these pigments due to the need to constantly launch vehicles with impressive innovations An example of this can be found in the use of vivid car finishes using these special effect pigments, which produce a dynamic appearance, far different from the solid finishes obtained with traditional solid coatings. Texture is defined as the variation of gray tones and the spatial distribution of them over an area [3,4] An example of this can be found in pigments known as goniochromatic, gonioapparent or effect pigments that show appearance variations as a function of the illumination and observation angles. The goniochromatic particles inside the pigment can generate specific spatial distributions that create additional optical effects dependent upon the angular configuration [5,6]
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