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Proceedings of the 90th JSCM Anniversary Conference
J. Jpn. Soc. Colour Mater., 91〔3〕，82–84（2018）

Novel Technique for Color and Appearance Measurement and Analysis
Prakash Kumar＊,† and Ayako Iwakoshi＊＊ Nippon Paint Automotive Coatings Co., Ltd., 2-14-1 Shodai-Ohtani, Hirakata-City, Osaka 573-1153, Japan†Corresponding Author, E-mail: prakash.kumar@nipponpaint.jp(Received November 28, 2017; Accepted February 8, 2018)

Abstract
The measurement and analysis of color and appearance is essential for design and approval of coatings in automotive industry. Novel methodto measure the appearance using color measurement of coated surface is investigated. The reflection of objects from coated surface undersimilar lighting condition is analyzed using new image analysis technique to compare appearance of coatings. Result shows good correlation
between visual perception and appearance measurement.
Key-words: Automotive, Clearcoat, Appearance, Color, Image analysisof 35 μm and cured in an oven at 140°C for 30 minutes toobtain finished panels for testing.
Digital images of the panels are obtained in controlled
light intensity at fixed reflection angle using high resolution
camera (Fig. 1). The image RGB values are obtained and low
pass filter is applied to the data. The appearance arithmetic
and root mean squared roughness parameters values

1．Introduction
The coatings appearance is one of the key requirementsin the automotive industry. There are several standards thatare used to determine the quality of appearance. One of themethods is by using the wave-scan instrument that provides
structure information in five distinct wavelengths based on
the reflection of light source over a surface1). It is widely
mentioned that the measured surface waviness in terms ofthese values are difficult to correlate well with the visualperception2) specially for colored painted panels3).
New technique is developed to analyze appearance fromdigital image of coatings. Instead of single laser source of
fixed wavelength, color image obtained from digital camera
could be used for analysis of surface appearance waviness.
Image of surface obtained under reflection of a light source
at a fixed angle and exposure can be used to quantitatively
determine the appearance. The image is digitally analyzed forvariations in pixels RGB value and calculation of roughness
based on variation in the numerical value of the color
coordinates. Human eyes visualizes color spectrum based on
the three primary colors red, green, and blue receptors, andimage analysis based on the RGB map of the surface is well
suited for the appearance as well as color analysis.

R a=1 n1 n
Σ yi and Rq= n Σ 1 yi2 are calculated based on then 1

plot of RGB pixels values yi across the image. Higher Ra
would imply more structure present in the surface withhigher waviness. The labelled panels are examined by fourpanelists independently providing rating from 1 to 5 with 5
being the best appearance. The surface roughness parameters
are measured by contact roughness meter Mitutoyo SJ-210
and correlated with the appearance roughness parameters.
The method is further extended to analyze the metallic
appearance and flip-flop measurement of effect coatings

2．Experimental section
E-coat steel panels of size 20 cm×10 cm are spray-coatedusing waterborne three-wet painting process with 20 μm
primer layer. Commercial grade automotive basecoat paintsof four colors namely red, blue, grey, and metallic silver withdifferent variations from Nippon Paint Automotive Co. Ltd.
is applied to a thickness of about 15 μm by spray coating on
panels. 2K solventborne clearcoats is applied to a thickness© 2018 Journal of the Japan Society of Colour Material

Fig. 1 Panel images sorted with color.

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