Validation of a gonio-hyperspectral imaging system based on light-emitting diodes for the spectral and colorimetric analysis of automotive coatings

Abstract

In this study, a novel gonio-hyperspectral imaging system based on light-emitting diodes for the analysis of automotive coatings was validated colorimetrically and spectrally from 368 to 1309 nm. A total of 30 pearlescent, 30 metallic, and 30 solid real automotive coatings were evaluated with this system, the BYK-mac and X-Rite MA98 gonio-spectrophotometers, and also with the SPECTRO 320 spectrometer for further comparison. The results showed very precise correlations, especially in the visible range. In conclusion, this new system provides a deeper assessment of goniochromatic pigments than current approaches due to the expansion of the spectral range to the infrared.

Review of instrumental inter‐agreement study of spectral and colorimetric data of commercial multiangle spectrophotometers

“…In addition, they provide visual texture effects (gloss, 11 sparkle 12 or glitter or glint, coarseness 13 or graininess, pearliness, 14 etc), and therefore it requires a complex instrument to characterize these materials completely, and to propose efficient models of visual and instrumental correlation for detection, scaling and discrimination (including tolerances 15,16 ). Thus, in many cases, a conventional optical set-up, 17 typically used in classical spectrophotometers or based on color-imaging systems, 18,19 both for diffuse or directional geometries, is not completely efficient for color management in these industries (automotive, etc. ) In general, a multiangle spectrophotometer characterizes the gonio-color appearance by measuring the spectral relative reflectance factor and the CIELAB values of the sample with different illumination and observation angles.…”

Texture Evaluation of Automotive Coatings by Means of a Gonio-Hyperspectral Imaging System Based on Light-Emitting Diodes

“…While measurements of sparkle, graininess and mottling are as yet not regulated by any standards, the proposed setup followed those applied to multi-angle color measurements issued by the German Institute for Normalization (Deutsches Institut für Normung, DIN, Berlin, Germany) and the American Society for Testing Materials (ASTM, West Conshohocken, United States): DIN 6175-2, ASTM E2194-09 and ASTM E2539-08 [37][38][39]. This decision was made because these effects were analyzed through a device previously developed for spectral and colorimetric assessments ( Figure 2) [35]. Essentially, this device (GOHYLED system, Centre for Sensors, Instruments and Systems Development -Universitat Politècnica de Catalunya, Terrassa, Spain) was composed of a spectrally tunable light source based on LEDs and two monochromatic cameras that covered the range from 368 to 1309 nm; and two rotation stages, one to control the observation and the other the illumination directions.…”

“…Since the BYK-mac ® works in the VIS, only the results obtained in this range were compared. The input data for all the assessments were reflectance images as in reference [35].…”

“…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]. This system can assess texture over a large area and from the ultraviolet (UV) to the IR range, thereby providing pixel-wise spectral information.…”

Graininess characterization by multidimensional scaling

“…The system characterizes samples by their spectral reflectance, and colour at different geometries, and also through the textural effects of sparkle, graininess and mottling. Regarding textural measurements, the graininess attribute is defined by specific indices, based mainly on first-and second-order statistics (19,20). The measuring area of this instrument was of 50 × 37 mm.…”