On the relations between color,gloss, and surface texture in injection‐molded plastics

The relation between color and gloss of injection‐molded plastic specimens was evaluated by means of a 45°/0° geometry spectrophotometer and a glossmeter. The specimens were plaques having one smooth, glossy field and one rougher, textured region made of two different polymeric materials (acrylonitrile‐butadiene‐styrene and polypropylene) in a range of colors. A significant influence of the lightness L* of the specimens on the measured gloss of the textured field, with a low gloss appearance, was found. This can probably be attributed to a contribution from bulk scattering, which is linked to the reflectance from within the specimen. The influence of texture on the measured color of the plaques was assessed by evaluating the color difference between the smooth field and the more textured area on the specimens. When the surface was textured, the color changed; in general it became lighter and less saturated. The magnitude of the change depended on the color of the material. The darker the material was, the larger was the increase in lightness L* as the surface became rougher. The shift in chroma C* was determined not only by the saturation but also by the lightness of the specimens. Darker specimens exhibited a larger decrease in chroma when the surface was textured. The change in the measured color caused by increasing the surface roughness could be predicted in a satisfactory manner using a model developed for xerographic printing paper. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 291–298, 2009     

Angle‐resolved light scattering from textured injection‐molded plastics

With regard to surface appearance, the angle‐resolved light scattering from textured polymeric surfaces was evaluated to link the reflectance properties to measured gloss as well as visually perceived gloss. Bidirectional reflectance distributions were determined by means of a scatterometer and the specimens involved were textured injection‐molded plaques manufactured from three different polymers; an acrylonitrile‐butadiene‐styrene (ABS) copolymer, a polypropylene (PP), and a polycarbonate and ABS copolymer blend (PC/ABS). The influence of color, surface roughness, and angle of incidence on the scattering characteristics was evaluated. An off‐specular reflectance peak was observed for the textured specimens the magnitude of which was clearly determined by the surface roughness and the angle of incidence. The color of the specimens mainly influenced the diffuse reflectance. The results provide a measure of perceived gloss and supported previously reported findings regarding the relevance of the concept of contrast gloss for the gloss characterization of textured polymeric surfaces. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Goniocolorimetry: From measurement to representation in the CIELAB color space

The classical definitions of color are well adapted to diffusing objects, whose color is almost independent of the viewing angle, and to very glossy object observed in the specular direction in respect to the light source. For glossy or iridescent objects, the color is difficult to characterize due to its dependence on the viewing direction. In order to cope with such objects and to represent their angle‐dependent colors in a colorimetric space, we adapt the CIELAB space to “goniocolorimetric” measurements. A crucial point when defining this space is the statement of the viewing solid angle. First, we suggest performing a BRDF measurement at high angular resolution in order to characterize the gloss of the specimen. Then, since for the definition of colors the CIE recommends cones of half‐angle of 2° or 10°, we propose to convert the measured BRDF into a reflectance factor defined in respect to these solid angles. This procedure is eased by a planar multispectral image of the BRDF, where solid angles are specified by the pixel size. At last, the reflectance factors are converted into CIELAB coordinates. By using this procedure, the perfect white diffuser but also the perfect mirror can be represented in this colorimetric space. © 2010 Wiley Periodicals, Inc. Col Res Appl, 36, 169–178, 2011;     

Modeling the appearance of metal‐like packaging printing

A study of the agreement between a visual assessment and the measurement of the reflectivity of printed metallic inks was performed. A psychophysical property for this percept was identified as visual brilliance. The visual judgments of a series of printed panels were compared with measurements from various types of specular reflectance instruments. The results showed that gloss does not linearly follow the appearance of highly reflective specular surfaces. It was observed that the visual assessment of brilliance was highly correlated to the normalized hemispherical diffuse reflectance factor difference. Further, visual brilliance could be mapped to a logarithmic function of the luminous specular reflectance factor and the measurement scale of log(Y) agreed with the scale of hemispherical diffuse reflectance. It was, thus, concluded that either of these measures may be utilized to establish aims and tolerances for production control of the reproduction of foil‐like prints. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 38–49, 2017     

The effect of gloss on color

A model was developed for the effect of gloss on reflected color, taking the measurement geometry of the color measuring device into account. It considers the total front surface reflectance of a given sample to be independent of gloss and determined only by its refractive index and the angle of the incident beam. Although the total front surface reflectance is fixed, its specular component increases (and the diffuse component decreases) with increasing sample gloss. Therefore, the diffuse reflectance factor measured by a spectrophotometer decreases with sample gloss. In this article, a defined curve was fitted to the measured reflectance factor of black xerographic print samples having a range of gloss values for the 0/45 and diffuse spectrophotometer geometries, and this curve was used to predict the CIELAB color values for samples of the other colors at various gloss levels. The predicted color was compared to the measured color for cyan, magenta, yellow, red, green, and blue images that spanned a wide range of gloss. The RMS color error between the predicted and measured color of all of these images was found to be about 3 CIELAB ΔE* units. © 1999 John Wiley & Sons, Inc. Col Res Appl, 24, 369–376, 1999     

Toward the soft metrology of surface gloss: A review

The most straightforward way to assess the glossiness of a surface is by measuring the specular reflectance by use of a specular glossmeter. Although alternative measurement methods have been proposed, this is still the most frequently used instrumental measurement technique for gloss evaluation until today. However, due to both the multidimensional nature of gloss perception and to the initial purpose of a specular glossmeter only to judge the gloss differences of surfaces with similar appearance, specular glossmeter results do not seem to provide a reliable basis for estimating the gloss appearance of a surface. During the past decades, increased attention has been paid to understanding how the human visual system arrives at a particular sensation of surface gloss, and which factors influence this process. This article was established in response to these new insights, and provides the reader an overview of the most important developments and findings regarding gloss measurement and gloss perception over the past 15 years. With the ultimate goal to achieve a better correspondence between gloss measurement and gloss perception in the future, issues of alternative measurement methods are considered, and some suggestions for relevant future research are proposed. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 559–570, 2014     

Goniochromatic properties of human tooth dentin

This study measured the goniochromatic properties of human tooth dentin through the viewing angle dependent color change measurement, and determined the influence of the microscopic structural nonuniformity of dentin surface on the gonioappearance. Color of 21 polished dentin specimens was measured by a spectroradiometer in wet and dry conditions. Spectral reflectance values were obtained with 0, 20, 45, and 70° aspecular viewing angles to the surface. These values were converted to CIE color coordinates (CIE L*, a*, and b*) relative to the specular set (0°) standard white tile to determine general goniochromatic effect, and to the same aspecular set standard white tiles to determine the influence of nonuniformity on dentin surface caused by dentinal tubules. Color coordinates and chroma were influenced by the viewing angle (P < 0.05). As to the influence of nonuniformity, CIE L* and a* and chroma were influenced by the viewing angle while CIE b* was not (P = 0.05). Goniochromatic effect of human dentin was confirmed instrumentally, and the nonuniformity of dentin increased goniochromatic effect. Based on these results, goniochromatic properties of intact teeth should be studied further, and restorative materials that can simulate these properties should be developed. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2012     

Surface reflectance estimation by the dichromatic model

A method is described for estimating the surface-spectral reflectances of glossy objects when the color signal is a mixture of diffuse reflections, specular reflections, and interreflections. The objects are inhomogeneous dielectric materials, and the reflected light is measured using a spectroradiometer. We first describe the main idea; the color signals, reflected from two closely apposed surfaces with a single interreflection between them, can be expressed by a linear combination of the illuminant spectrum and two diffuse spectral reflection functions. We introduce a representation in which each of these three terms is projected onto a point on a unit sphere. Estimation of the diffuse reflection functions is then reduced to finding the vertices of the spherical triangle. Next, an algorithm is described to estimate the locations of the vertices of diffuse reflectance functions from the measured samples. The reliability of the algorithm is demonstrated in an experiment using two plastic objects with glossy surfaces. © 1996 John Wiley & Sons, Inc.     

The Influence of the Measuring/Viewing Angle on the Color of Injection-Molded Plastics

A multi-angle spectrophotometer was used to measure the CIELab coordinates L?, a? and b? in different angles relative to the incident light. The specimens used were acrylonitrile-butadiene-styrene injection-molded plaques in different colors and with different surface textures. Variations in the coordinates when changing the measuring angle depended on the color and the texture. In general, however, smooth (glossy) surfaces were measured to be darker and of higher chroma than textured surfaces and as the gloss of the surfaces decreased (due to texturing), the lightness of the surfaces increased and the absolute values of a? and b? decreased over the range of measuring angles (not too close to the specular reflection angle). A psychometric study involving a human test panel was used as a complement to the measurement. The agreement between the measurements and this study cannot be said to be satisfactory, unless the variation in the color coordinates was quite clear. Possible reasons are discussed.     

Quantification and prediction of visually perceived specular gloss at three illumination/viewing geometries

In the present study, attempts were made to clarify the existence of a correlation between visually perceived and instrumentally measured specular gloss of a series of achromatic samples. To this end, seven achromatic physical scales of specular gloss each consisting of 10 or 11 samples were prepared using lithographically printed black, white, and five in between gray papers. The samples were visually assessed and subsequently quantified in terms of a visually uniform color constant lightness scale, by a panel of 14 observers in an especially designed unidirectional light compartment at three illumination/observation geometries, namely 20°/20°, 60°/60°, and 85°/85°. Four statistical parameters were utilized to determine the correlation between visually perceived and instrumentally measured specular gloss. The results show that the instrumental 60°/60° geometry is capable of efficiently quantifying the equivalent specular gloss as perceived by a human observer. Surprisingly, it was also possible to accurately predict the visually quantified specular gloss both at the 20° and the 85° geometries by the aid of applying special linear relationships derived from the instrumentally measured specular gloss of the 60° geometry.     

Influence of surface roughness on the diffuse to near‐normal viewing reflectance factor of coatings and its consequences on color measurements

In this work, we discuss the effect of surface roughness on the measurement of the diffuse to near‐normal viewing reflectance factor of coatings and evaluate its impact on the corresponding color coordinates. We compare specular component included (SCI) and excluded measurements. We introduce a gloss‐factor to account for surface roughness in specular component excluded measurements. We present experimental results on samples with different degrees of surface roughness. Samples in this study were chosen to expose the contribution of the surface in the reflectance factor. For slightly rough surfaces, the influence on the measured reflectance factor depends on whether the specular‐component is included or excluded. As the surface roughness increases, the specular‐excluded reflectance factor increases approaching its value with the SCI further roughness lead to similar measurement results in both configurations. © 2012 Wiley Periodicals, Inc. Col Res Appl, 38, 177–187, 2013.     

Specular gloss versus surface topography for oil‐filled nanoparticle coatings on paper

The appearance or printing quality of paper surfaces is mostly characterized by their glossiness, measured with a glossmeter as specular reflectance. The gloss properties of a base paper substrate can be improved after application of a poly(styrene‐co‐maleimide) nanoparticle coating under pure conditions or in the presence of different vegetable oils. The specular gloss properties of 11 different nanoparticle paper coatings have been determined under 75° and 85° incident light angles, with good relation between values along parallel (machine) and perpendicular (transverse) direction. The gloss properties for the different coatings have been further related to the surface topography. Therefore, the statistical and spatial surface roughness parameters have been studied in detail at two length scales including non‐contact profilometry (1 × 1 mm²) and atomic force microscopy (2 × 2 μm²). Based on values of the Rayleigh parameter for non‐contact profilometry, the surfaces can be considered as optically rough. The gloss values cannot be directly related to statistical surface roughness parameters. Otherwise, an experimental power‐law model for gloss has been proposed as a function of (β/Sq) with correlation length β and root‐mean‐square roughness Sq. A best‐fit model illustrates that gloss properties of various nanoparticle paper coatings mainly relate to the spatial surface roughness parameters determined from non‐contact profilometry. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 596–610, 2016     

Evaluating contrast gloss of textured polymeric surfaces

The concept of contrast gloss and its relation to visually perceived gloss was examined for textured polymeric specimens. The specimens were injection‐molded plaques manufactured in three different polymers (acrylonitrile‐butadiene‐styrene copolymer, polypropylene, and a blend of polycarbonate and acrylonitrile‐butadiene‐styrene copolymer). A contrast gloss factor was determined from the reflectance data obtained with a conventional multiangle spectrophotometer. To evaluate the visual impression of gloss of the specimens a psychometric study was performed. The contrast gloss factor corresponded well with the visual assessment of the gloss and it was able to discern the visual differences between several specimens not significantly discriminated by their gloss values. These latter gloss values were obtained with a conventional glossmeter measuring specular gloss. In correspondence with the visual assessments and practical experience, the relation between the contrast gloss factor and the specular glossmeter measurements was found to depend on the type of polymer used. When evaluating gloss of specimens varying in color, the contrast gloss factor corresponded well with the visual assessments. This was in contrast to the specular glossmeter measurements which ranked the specimens essentially in the opposite order. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

NIST reference goniophotometer for specular gloss measurements

The measurement of specular gloss consists of comparing the luminous reflectance from a test specimen to that from a gloss standard, under the same geometric conditions. The reference goniophotometer described here was designed and characterized to comply with the geometric and spectral conditions specified in the international documentary standards for specular gloss measurements at the standard geometries of 20, 60, and 85°. In addition, this instrument measures the bi-directional luminous reflectance and transmittance for incident angles from 0 to 85°. The goniophotometer and the measurement procedures used to determine the specular gloss of nonmetallic samples are described in this paper, as well as the characterization of the instrument and uncertainty analysis. The minimum relative expanded uncertainty (k=2) for the reference goniophotometer is 0.3%. Optical Technology Div., Gaithersburg, MD 20899-8441.     

Repeatability and reproducibility of specular gloss meters in theory and practice

In order to numerically quantify and to ensure consistency of the visual appearance of the end product, many industries perform color and gloss measurements, through the results of which they define maximum tolerances during quality control. For this, they may primarily rely on precision data for repeatability and reproducibility as reported by instrument manufacturers, who develop their instruments according to standardized measurement geometries defined in international standards. This paper reports on an investigation of the inter-instrument agreement between specular gloss meters which conform to universally adopted gloss standards. Six commercially available instruments, manufactured by three different companies, and twenty-five gloss artifacts, with specular gloss values ranging between 2 and 110 gloss units (60° geometry), were selected for use in the study. The repeatability and reproducibility of the instruments were assessed according to the criteria described in ASTM D523-14 and ISO 2813:2014, and to the specifications reported by the instrument manufacturers. Ray tracing simulations were performed by use of the bidirectional reflectance distribution function measurement data of two samples, and based on the standardized optical design of the specular gloss meter, in order to get a better insight on the expected tolerances of the gloss readings from a theoretical point of view. On average, the practical results indicate that both the repeatability and reproducibility values are higher than those specified in the recommendations and by the manufacturers. Ray tracing simulations confirm this finding. While specified repeatability and reproducibility thresholds are based on ideal standards, in practice, there are parameters that can lead to significant higher deviations. Care should therefore be taken when analyzing measurement results obtained from different instruments, and when defining tolerances for evaluation of gloss measurements.     

Effect of sodium chloride,sodium tripolyphosphate and pH on color properties of pork meat

The myoglobin state determines the color of meat, and most of the additives used in processing meat products cause color changes. The aim of this study was to quantify the effect of pH (4.0, 5.0 and 6.0), sodium chloride (0, 1.5 and 3.0%) and sodium tripolyphosphate (0, 0.15 and 0.30%) on the color properties and myoglobin states of pork meat (Subscapularis muscle). CIELAB color parameters (Lightness, redness, yellowness, chroma and hue) and reflectance spectrum, between 400–700 nm, were obtained. The different myoglobin forms (deoxymyoglobin, oxymyoglobin and metmyoglobin) were quantified using K/S reflectance values. Both, sodium chloride and tripolyphosphate reduced meat lightness, although the latter additive did not modify redness, yellowness, chroma or hue, but stabilized the percentage of oxymyoglobin. A decrease in pH and the addition of sodium chloride or sodium tripolyphosphate, led to an increase in the Metmyoglobin percentage. © 2003 Wiley Periodicals, Inc. Col Res Appl, 29, 67–74, 2004; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/col.10215     

A new approach to appearance characterization

A proposal to characterize appearance in three different categories—color, cesia, and spatial properties or spatiality—is made. Color will include whiteness and yellowing and is related to optical power spectral properties of the stimulus detected by observers. Cesia will include transparency, translucence, gloss, luster, haze, lightness, opacity, matt, etc., and is related to the properties of reflecting, transmitting, or diffusing light by objects or materials evaluated by human observation. Spatial properties are divided in two main groups: (1) modes of appearance in which color is modified depending on the angle of observation related to the light incidence angle, such as metallic, pearlescent, or iridescent materials, and (2) modes of appearance related to optical properties of surfaces or objects in which effects of ordered patterns (textures) or finishing characteristics can be described by spatial filtering (roughness, polish, distinctness of image, orange peel, etc.). © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 164–167, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20205     

Diffuse reflectance‐factor measurements of rose petals

The diffuse reflectance factor for different colored rose petals is measured as a function of wavelength using a high resolution optical spectrometer. The tristimulus values, the CIE chromaticity coordinates, the dominant wavelength and purity, the CIE whiteness index, the tint index, the CIE 1976 LAB coordinates, as well as CIELAB hue‐angle and chroma are reported. The data on diffuse reflectance factor are presented in the 390?800 nm range at intervals of 10 nm. Using the data, one can generate the perceived color of the roses and the color coordinates in different illuminating light sources and environments. The present data will be useful for the color characterization of flowers, realistic rendering of flowers in computer graphics, color photography, and in the development of filters for color photography. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2011     

Optical and surface properties of whey protein isolate coatings on plastic films as influenced by substrate,protein concentration,and plasticizer type

Composite film structures of common plastic polymers including polypropylene (PP) or poly(vinyl chloride) (PVC) with whey protein isolate (WPI) coatings may be obtained by a casting method. Optical and surface properties of the resulting WPI‐coated plastic films, as affected by protein concentration and plasticizer type, were investigated to examine the biopolymer coating effects on surface modification with polymeric substrates of opposite polarity. The measured properties involved specular gloss, color, contact angle, and critical surface energy. Regardless of the substrates, WPI‐coated films possessed excellent gloss and no color, as well as good adhesion between the coating and the substrate when an appropriate plasticizer was added to the coating formulations. The protein concentration did not significantly affect gloss of WPI‐coated plastic films. Among five plasticizers applied, sucrose conferred the most highly reflective and homogeneous surfaces to the coated films. The WPI coatings were very transparent and the coated films with various protein concentrations and plasticizers showed no noticeable changes in color. Experimental results suggest that WPI coatings formulated with a proper plasticizer can improve the visual characteristics of the polymeric substrate and enhance water wettability of the coated plastic films. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 335–343, 2004     

Comparison of color gamuts among several types of paper with the same printing technology

In this work, we have studied the relationship among the colorimetric properties of different types of paper, having different finishing and grammage. Their color reproduction capability has also been analyzed by using the same printing technology (inkjet printing). On the one hand, we have plotted CIELAB data under the illuminant D50 into constant lightness and hue‐angle planes to be compared with MacAdam limits and with Pointer's real‐world surface color. On the other hand, we have calculated the volume gamut of the color solid associated to each color paper gamut. Analyzing the results, we have checked that there is not any clear relationship among the colorimetric properties of paper (for instance, CIE whiteness index, etc.) and the color gamut volume associated. However, the colorimetric parameters associated to the printed sample showed a quite good linear correlation between the minimum lightness (or the maximum blackness value) of the printed color chart and the color gamut volume. In particular, the greatest color gamut volume corresponds to the glossy papers taking into account this correlation for inkjet printing. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 330–336, 2009