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Billmeyer and Saltzman's principles of color technology, 3rd edition
Abstract
This is a textbook at the entry level on the industrial technology of colorimetry. This paper is a review of that textbook. The copyright is owned by John Wiley & Sons and reprints are only available through the publishers.
... accounting for the Tiff file encoding and a linear matrix. (See Berns (2000, 2001) for a numerical example.) Comparisons are listed in Table 1. ...
... Target Mean ∆E 00 Maximum ∆E 00 Standard deviation ∆E 00 ColorChecker DC 1.9 13.7 1.8 Gamblin 2.4 7.1 1.6 'Un-ageing' La Grande Jatte The optical behaviour of La Grande Jatte was modeled using Kubelka–Munk turbid-media (KM) theory (Nobbs 1985, Berns 2000 ...
Georges Seurat first used his divisionist painting technique on A Sunday on La Grande Jatte - 1884 beginning in October 1885. Painting with pigments representing colours seen in the visible spectrum that were minimally mixed on the palette and using divided brushstrokes, he aimed to impart luminosity to the surface and to explore 19th century ideas of colour theory, such as simultaneous contrast. Pigment analysis has disclosed that the brushwork containing zinc yellow has darkened significantly: Yellow, green- yellow, and orange brushstrokes have become brown, olive-green, and reddish brown, respectively. Additionally, the painting has further darkened due to the natural ageing of the oil medium. By performing spectral reflectance measurements in situ on darkened areas of the painting and on paint-outs of comparable unaltered colours, using Kubelka-Munk turbid media theory, imaging the painting with colour-managed digital photography, and image editing with Adobe® Photoshop®, a digital version of the original, more luminous appearance of La Grande Jatte was simulated.
... Possible color alterations after the treatment were evaluated through the total color change ΔE* in the CIE L*a*b* color space [43] by means of a portable colorimeter (PCE-CSM-4 from PCE instruments), using as references illuminant D65 and observer CIE 10 • . The measurements were performed on six specimens per treatment and mockup type (for a minimum of 24 measurement points). ...
Many of the concrete structures that conform our modern cultural heritage are in need of repair and protective interventions. Silane-based impregnation treatments can be used to repair onset cracks and reinforce the surface due to their ability to produce silica and C-S-H gels, and can be modified by incorporating hydrophobic precursors to create multifunctional treatments that also protect from water ingress.
Since the effectiveness of impregnation treatments is dependent on substrate properties and chemical-physical changes it may have experienced over time, validation using standard materials may not always be representative of on-site application. In this work, the effectiveness of three innovative silane-based impregnation treatments developed by our group (two of them combining superhydrophobic properties) was evaluated on mockup specimens, which simulate the properties of the cementitious materials from six different heritage structures across Europe, artificially aged to simulate weathering by three methods: carbonation, chloride ingress and physical damages (freeze–thaw and thermal cycles).
The characterization of the treatments showed they are compatible in terms of chemical interaction, applicability and minimal aesthetical alterations. Surface resistance and ultrasound pulse measurements have been used to assess the improvement in mechanical properties. The incorporation of hydrophobic components and fumed silica has a relatively low impact over the mechanical properties while it significantly reduces water absorption and grants water repellent properties to the surface, giving rise to a superhydrophobic performance.
... The color changes induced by the treatments on the stone were evaluated by measuring the total color difference ΔE* [50] by means of a solid reflection spectrophotometer (Colorflex model from HunterLab). Conditions used were illuminant D65 and observer CIE 10 o . ...
The decay of building materials is generally caused by the combination of chemical, physical and biological agents. Therefore, the development of products that combine multiple protection mechanisms is desirable. We have developed, via a sol-gel route, CuO/SiO2 nanocomposites with application as a multifunctional protective treatment for building stones. In this work, we demonstrate that CuONPs act as a catalyst of the sol-gel process and promote the formation of nucleation centers, affecting the final structure of the nanocomposites. We also conclude that the nanocomposites increase mechanical resistance and decrease microbial growth of two reference laboratory microorganisms (bacteria and yeast) on a typical building limestone. Moreover, the release of Cu2 + ions is the most likely mechanism for the biocidal effect. Finally, we find that the highest concentration of CuONPs, in the studied range (0.00–0.35% w/v), was not the most effective because it causes a NPs precipitation, decreasing the biocidal effect, and the resulting material is heterogeneous and fragile. An intermediate proportion of CuONPs provides a suitable consolidant and biocide performance.
... Negative a* axis gives chromatically the green and positive a* axis gives chromatically the red. The positive b* axis gives chromatically the yellow and negative b* axis gives chromatically the blue.22,23 ...
PURPOSE
The color of the ceramic restorations is affected by various factors such as brand, thickness of the layered the ceramic, condensation techniques, smoothness of surface, number of firings, firing temperature and thickness of dentin. The aim of this study was to evaluate the color change and surface roughness in dental porcelain with different thicknesses during repeated firings.
MATERIALS AND METHODS
Disc-shaped (N=21) metal-ceramic samples (IPS Classic; Ivoclar Vivadent; Shaar, Liechtenstein) with different thickness were exposed to repeated firings. Color measurement of the samples was made using a colorimeter and profilometer was used to determine surface roughness. ANOVA and Tukey tests with repeated measurements were used for statistical analysis.
RESULTS
The total thickness of the ceramics which is less than 2 mm significantly have detrimental effect on the surface properties and color of porcelains during firings (P<.05).
CONCLUSION
Repeated firings have effects on the color change and surface roughness of the dental ceramics and should be avoided.
... According to these values, the colour surface of all samples changed significantly throughout the experiment, as variations in three CIELAB units are considered as the lower limit of perceptibility of differences in the colour (Benavente et al., 2003; Grossi et al., 2007; Prieto et al., 2010b,c). Even assuming higher thresholds, such as five CIELAB units (Berns, 2000; Völz, 2001; Gómez-Robledo et al., 2008) or six CIELAB units (Hardeberg, 1999), all values of the total (DE* ab ) and partial (DC* ab ) colour differences obtained greatly exceeded these thresholds. Moreover, these results again indicate that none of the treatments were successful because in all cases the colour change produced in samples treated with the plastic-based products was greater than the colour change in the untreated samples (positive control). ...
... So, these loci refer to the average Munsell value of the charts. According to Berns (2000), in a perfect match between the Munsell variables and CIELAB, these loci of constant hue and chroma would be a symmetrical and circular 'spider-web' plot. The chart USA2000 approaches this condition rather well (Figure 1a). ...
Soil color charts, which contain standard color chips arranged following the Munsell system, are useful tools for visual assessment of soil color in the field and laboratory. Several editions of these charts, manufactured in USA and Japan, are used indifferently by soil scientists. One new and one old edition of both USA and Japanese soil color charts have been studied here in CIELAB color space, assessing the regular spread of their color chips. We plotted the loci of constant Munsell hue and chroma on the a*b* plane, and computed color differences between neighboring chips (∆L*, ∆C*, ∆H*). In the new editions, USA charts proved to have greater average lightness and chroma steps (∆L*=9.90, ∆C*=5.86) than Japanese charts had (∆L*=8.98, ∆C*=5.36). Irregularities in the measured values of L* C* h were found in the old Japanese chart with respect to the new one, including lower values of the average steps: lightness-, chroma- and hue-difference reduced by 18%, 13%, and 21%, respectively. The same trend was also found for the old USA charts, but with less reduction. It can be concluded that chips with the same Munsell notation may have different colors in different soil color charts.
... The use of the simplified K-M theory for the opaque case is well established in practice and well described in the literature. [7] [8] [9] [10] Practical successes have been achieved by the reduction in mathematical complexity and elimination of controlling thickness. The simple opaque assumption was made for this investigation. ...
Compared with colorimetric imaging, multispectral imaging has the advantage of retrieving spectral reflectance factor of each pixel of a painting. Using this spectral information, pigment mapping is concerned with decomposing the spectrum into its constituent pigments and their relative contributions. The output of pigment mapping is a series of spatial concentration maps of the pigments comprising the painting. This approach was used to study Vincent van Gogh's The Starry Night. The artist's palette was approximated using ten oil pigments, selected from a large database of pigments used in oil paintings and a priori analytical research on one of his self portraits, executed during the same time period. The pigment mapping was based on single-constant Kubelka-Munk theory. It was found that the region of blue sky where the stars were located contained, predominantly, ultramarine blue while the swirling sky and region surrounding the moon contained, predominantly, cobalt blue. Emerald green, used in light bluish-green brushstrokes surrounding the moon, was not used to create the dark green in the cypresses. A measurement of lead white from Georges Seurat's La Grande Jatte was used as the white when mapping The Starry Night. The absorption and scattering properties of this white were replaced with a modern dispersion of lead white in linseed oil and used to simulate the painting's appearance before the natural darkening and yellowing of lead white oil paint. Pigment mapping based on spectral imaging was found to be a viable and practical approach for analyzing pigment composition, providing new insight into an artist's working method, the possibility for aiding in restorative inpainting, and lighting design.
... Many colour scales has been developed for this purpose Berns [3]. Most frequently used system CIELAB was designed in 1976 year. ...
Age-related colour changes of biological objects are the results of changes in structure and properties which may reflect the influence of the extrinsic and intrinsic environment. The method able to discriminate these two factors was not published yet. Non-erupted teeth which are isolated from the environment of the oral cavity (intrinsic factors) have not yet been explored too. A device for research the dentist's chair-side measurements of vital erupted teeth as well as extracted impacted teeth (immediately after extraction) was built from commercially supplied components (fiber optic spectrometer) coupled with specific custom-made parts and a specific software driver. The measurement method related tooth for total colour changes in system CIELAB 1976 was evaluated to be inadequate. For more precise method of the ∆ECMC(l:c) were theoretical trichromatic coordinates of standard tooth and the ratio of extrinsic and intrinsic factors for vital erupted and impacted teeth modelled by multivariate 3D-mathematical regression models. The rate of complex discolouration caused by the total factors decreases over the life of humans. The rate of colour changes caused by intrinsic factors is nearly constant over the life-time. Age estimation of the vital erupted teeth 21 (inversion exponencial function of CMC(2:1)) will be only approximate (s.d. 6.2 years). More convenient for approximate age estimation are the impacted teeth immediately after extraction (inversion linear function of CMC(2:1)), significant correlation with the known real age p-value < 0.001, (s.d. 3.1 years). Correlation between the subjects age and the yellowness of b* values of skulls is significant (r 2 = 0.80). The similar correlation between the subjects age and yellowness of b* values of impacted teeth (r 2 = 0.79) suggests a presumably similar mechanism of colour changes in bone and impacted teeth. These teeth are relatively available biological samples and can be obtained without any difficult medical or ethical issue.
... : Example of a single-chip sensor sensor spectral sensitivies are not a linear combination of the CIE standard observer [4] ones, they lead to false colors [10]. Using multispectral technology, colorimetric acquisition , capturing of metamere colors and the correct simulation of different illuminations become possible. ...
In this paper, we introduce a new camera concept – a multispectral camera with a color filter array well-known from common RGB cameras. The proposed system provides ap-proximately the color fidelity of a multispectral camera while featuring the compactness and – in principle – the low costs of an RGB camera. After a review of an RGB camera and a widely used in-terpolation algorithm we introduce the new camera type and provide a new interpolation algorithm which retains approximately the sharpness of the original multispectral image. We accomplish this by lowpass filtering of color channel differences. Comparison results for the new interpolation al-gorithms as well as a comparison of the multispectral and the RGB system concepts are provided.
The purpose of this study is to evaluate the factors affecting the assessment of granite color, such as grain size and texture, and to propose a methodology for this task which would reduce the margin of error associated with this procedure. For this purpose, an evaluation was carried out on the color of several granites with different textures used in the dimensional stone industry to highlight the importance of the sample area, the number of measurements per sample and the aperture of the equipment. A colorimeter was used to measure the granite color according to the CIE-L*a*b* and CIE-L*C*abhab systems, in both large slabs and small samples selected in a processing plant of ornamental granites. Granite color characteristics from large slabs had to be obtained with at least 60 shots due to the variation between different slabs. Therefore, several samples are needed for granite characterization. The color of gray granites does not vary significantly. Nevertheless, the more weathered granites show significant differences which are more evident in the b*-parameter, or the yellow–blue component, which allow the use of the colorimeter for quality control. By doing so significant differences among the rock pieces used in a single building can be avoided. There were no significant differences found in the color parameters from distinct apertures. However, due to the heterogeneity of the granite the color is evaluated better with larger apertures. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2012
Color science is the science that studies the properties of color and their application in different areas of life. More complex emotional states produce colors in works of art. Their impact far beyond the immediate sensations associated in stable and strong feelings. The same meaning is embedded in the words of the great Soviet artist Kuzma Petrov-Vodkin "There are colors and soothing irritation, screaming, arguing with each other and living together gently. In their fight or consent is born their impact on human." Johann Wolfgang Goethe was among the first researchers in the field of color perception. He dedicates this study almost two decades and the first links between the different effects of color with mental processes.
The color inconstancy of prints is related to the ink spectral properties and the lookup table for multi- ink printing systems. In this paper, color inconstancy was investigated for several ink-jet printers based on their ink set and the default lookup tables. A virtual model for each printer was created to determine the range of color inconstancy that a specific ink set could achieve. The color inconstancy performance of each default lookup table was evaluated by evaluating the color inconstancy of a printed test target. The optimum combinations of three- and four-chromatic inks were investigated to minimize the color inconstancy and keep a relative large color gamut simultaneously. The results showed that the color inconstancy can be decreased significantly without compromising the reproduction colorimetric accuracy. Moreover the color inconstancy can be improved by appropriate ink design.
Visible reflectance spectrophotometry is a valuable tool in art conservation. In particular, the spectral data can be used to evaluate potential pigment combinations for inpainting to insure metamerism is minimized. This is a critical criterion because of the wide range of museum lighting and observers, including imaging devices. Recently, a new method of pigment selection for inpainting was devel- oped that successfully minimizes metamerism. Normally, small-aperture spectrophotometers are used. An experiment was performed to test whether this technique could be used with direct digital capture of artwork. Multi-filter colour images were used to estimate spectral reflectance factor. The accuracy of the spectral estimation depended on the spectral properties of the system calibration target. The new method of pigment selection was able to correctly identify pigments from the estimated spectra in many cases. The reported results focus on blue pigments, often a cause of significant metamerism when poorly matched.
When a pair of common second-surface plane mirrors face each other, repeated mirror-to-mirror reflections form a virtual optical tunnel with some unusual properties. One property readily analyzed in a student experiment is that the color of objects becomes darker and greener the deeper we look into the mirror tunnel. This simple observation is both visually compelling and physically instructive: measuring and modeling a tunnel's colors requires students to blend colorimetry and spectrophotometry with a knowledge of how complex refractive indices and the Fresnel equations predict reflectance spectra of composite materials.
Differences in fabric may explain why relationships between aggregate stability and soil color have never been reported for a relatively narrow-ranging population of soils. Therefore, three size fractions (1–2, 0.25–1, and 0.05–0.25 mm) of 25 topsoils (75 samples) from a Regosol–Umbrisol soilscape (Sierra Nevada, SE Spain) were characterized for fabric by scanning electron microscopy, aggregate stability by wet sieving, and CIELAB color (hab, L*, C*ab) by diffuse spectral reflectance. A stability-index ranking from 0.17 to 0.98 paralleled a ranking of hab (88.5 to 66.1), L* (48.3 to 30.2), and C*ab (7.6 to 18.9): that is, the progressive increase in stability was related to increased soil redness, darkness, and chromaticity. The reason was an increase in binding agents such as clay, organic C, and free forms coating the surfaces of the aggregates. The values of the correlation coefficients (0.55 to 0.82), factor-analysis variances (73 to 88%), and multiple-regression coefficients (0.40 to 0.65) indicated, however, that much of the variability in stability cannot be statistically explained by color changes. Size fractions of soils with a similar binding-agent content did not significantly (P < 0.05) differ in color but they did in aggregate stability. They also showed fabric differences, indicating that the coatings are similarly effective as coloring, while their stabilizing capacity is regulated by size, shape, and arrangement of particles. A close packing of mixed silt sizes stacked like roof tiles resulted in a stable fabric itself. Color can indicate aggregate stability, depending on the binding-agent content, but, being insensitive to the inner particle arrangement, it cannot provide a complete prediction.
Virtual Reality (VR) has great potential to become a
usable design tool for the planning of light and colour in
buildings. However, the complex interaction between light
and objects makes the problem of lighting scenes a central
conceptual and practical problem of computer graphics. This
paper aims at discussing the problem of translating reality to
its digital counterpart. We deal with methodological issues
concerning how to compare visual results between different
media, mixed adaptation and arbitrary parameter setting in
the software. Our comparison between a 25 m2 real room and
different VR-simulations showed various problems related to
the translation and comparison of reality to VR.
Data were collected from video recorded interviews with
56 observers. Colour appearance was assessed with semantic
descriptions, magnitude estimation and colour matching.
Measurements of reflectance, luminance and spectral
composition were made.
This article investigates the impact of sulfur dioxide attack, deposition of dark particles in urban environments and laser cleaning with Nd:YAG 1064 nm on color change in a range of ornamental limestones. We have used the CIELAB and CIELCH systems to compare the relative importance of the variation of each coordinate for the color change. Sulfur dioxide and dark particle deposition seems to increase the chroma, most particularly in the yellow component. Particle deposition also leads to an obvious darkening of stone surfaces. Laser irradiation at 1064 nm affects the red component of limestone, particularly if they already possess a reddish color. In general, the more intense the original color of the stone the greater are the chromatic changes, but the direction change of the color-parameter affected by a particular process remains the same. It has always been apparent in an atmosphere heavily polluted with soot that the main changes to light-colored stones are the exponential decrease in the parameter L* (darkening–blackening). This has important aesthetic and social implications. However, in the near future it may be that in cleaner atmospheres, perhaps more dominated by organic pollutants, a yellowing process may be of greater concern. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 320–331, 2007
In spite of color being one of the physicochemical parameters most commonly used to characterize ornamental stone, there is yet no standardized protocol for measuring this parameter. Such a protocol is of particular importance for characterizing the color of heterogeneous surfaces, as in the case of granite. The aim of the present study was to determine the minimum area and the number of measurements required to characterize the color of granite rocks. A spectrophotometer and a tristimulus colorimeter, were used to measure the color of granite samples, and the measurements were expressed in CIE L*a*b* color system units. Three parameters were considered as variable factors: the type of rock (Labrador Claro, Grissal, Rosa Porriño, and Blanco Cristal), surface finish (polished, honed, sawn, and flamed), and target area (circular apertures of diameter 5, 8, 10, and 50 mm). The results of the application of multivariate analysis of variance and of the classical CIELAB formula and CIE L*a*b*-based color-difference formulae (i.e., CIE94 and CIEDE2000) to the data revealed that, although all considered factors affected the minimal area and the number of measurements required, the different circular apertures of both the instruments can be disregarded if the number of measurements and area recommended in this study are used. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010
Three psychophysical experiments were conducted to investigate the colour appearance changes between different sizes under various media or viewing conditions. The results are highly consistent that when increase stimulus size, the colour will appear to be lighter and more colourful with little change in hue. © 2010 Wiley Periodicals, Inc. Col Res Appl, 36, 201–209, 2011;
A review of electrochromic (EC) polymers and their applications in absorption/transmission, reflective, and patterned electrochromic devices (ECDs) is presented. Fundamental properties of EC materials such as optical contrast, coloration efficiency, switching speed, and stability are described along with the commonly used characterization methods. The origin of electrochromism in conjugated polymers is explained in terms of the electronic structure changes in the backbone upon doping/dedoping. The ability to tailor the EC properties of conjugated polymers and tune their color states via modification of the polymer structure is demonstrated. Multicolor electrochromic materials can be obtained by substitution of a parent polymer and controlled polymerization of comonomers and with blends and laminates of homopolymers. Absorption/transmission-type ECDs from complementarily colored polymers and reflective-type ECDs on metalized substrates are illustrated with several examples from the literature. Finally, several patterning methods that are promising for ECD applications are discussed. Examples of ECDs constructed from patterned electrodes using line-patterning, screen-printing, and metal vapor deposition techniques are investigated for their possible use in commercial applications.
Standardized in 1976 as a uniform color space, CIELAB is extensively utilized in color science and engineering applications. CIELAB provides both a color difference formula and correlates for common perceptual descriptors of color. Deficiencies in both areas are well-known, and based on these known limitations, numerous fixes have been developed yielding alternative color difference formulae that are derived as modifications of the color difference in CIELAB. In addition, several new color appearance spaces have also been proposed as modifications of the basic CIELAB framework. In this paper, we point out other, lesser-known and poorly-appreciated, limitations of CIELAB that occur particularly in the dark regions of color space. We demonstrate via examples, how these limitations not only cause performance compromises but lead to fundamental breakdowns in system optimization and design problems, making CIELAB unusable in these problems. We consider the reasons why these fundamental limitations were overlooked in the original development of CIELAB and analyze the mathematical representations contributing to the undesired behavior. We argue that fundamental new research is required to overcome this dark side of CIELAB; the development of uniform color spaces and new color appearance spaces must be revisited afresh using new experimental data and keeping in mind newer devices and applications.
In practice, most metameric pairs do not achieve colorimetric equality for a set of reference conditions. These parameric pairs are composed of a residual color difference and a metameric difference. Three techniques have been used to correct this residual color difference: an additive correction in L*a*b*, a multiplicative correction in XYZ (recommended by the CIE), and parameric decomposition where the batch's spectrum is adjusted. Parameric decomposition can be viewed as batch correction using three “colorants” (process primaries) where the color-mixing model is linear in reflectance. Most often, Cohen and Kappauf's Matrix R technique is used where the primaries are color matching functions. Alternative primaries were derived from a Munsell Book of Color and an automotive paint system using principal component analysis (PCA) and independent component analysis (ICA). 1,152 parameric pairs about 24 color centers were synthesized using the paint system and Kubelka–Munk turbid-media theory. Each parameric pair was corrected to a metameric pair using these methods. Spectral accuracy was evaluated by comparing the corrected spectra to metameric reference spectra calculated using Kubelka–Munk batch correction. The Matrix R technique had the worst spectral accuracy under the reference conditions while both PCA and ICA had similar and reasonable accuracy. The special index of metamerism, change in illuminant, was calculated for each parameric pair using these various correction techniques to achieve colorimetric equality. The Matrix R and CIE-recommended multiplicative techniques were statistically significantly worse than parameric decomposition using Munsell Book of Color PCA and ICA and automotive ICA process primaries. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 293–303, 2007
The influence of surface roughness on color change in several Spanish building stones is studied in samples of the following: Red Alicante, Black Marquina, White Macael, and Yellow Triana. In an experimental laboratory test (acid attack), we simulated the weathering process and made a comparative analysis between this and the polishing process. Changes in both color and roughness were measured during these processes. In limestones with medium or high chroma (Red Alicante) and both low chroma and lightness (Black Marquina), the total color changes were particularly affected in both the polishing and acid attack processes. On the other hand, in marbles with both low chroma and high lightness (White Macael and Yellow Triana), the total color changes were almost imperceptible in both processes. However, no change occurred in the hue of any of the analyzed stones. Spectrophotometric data showed that color change was due mainly to changes in surface roughness and not to chemical reactions that may have altered the oxidation state of the chromophore in the chromogen of the stone. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 343–351, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10178
Several methods to determine the color gamut of any digital camera are shown. Since an input device is additive, its color triangle was obtained from their spectral sensitivities, and it was compared with the theoretical sensors of Ives-Abney-Yule and MacAdam. On the other hand, the RGB digital data of the optimal or MacAdam colors were simulated to transform them into XYZ data according to the colorimetric profile of the digital camera. From this, the MacAdam limits associated to the digital camera are compared with the corresponding ones of the CIE-1931 XYZ standard observer, resulting that our color device has much smaller MacAdam loci than those of the colorimetric standard observer. Taking this into account, we have estimated the reduction of discernible colors by the digital camera applying a chromatic discrimination model and a packing algorithm to obtain color discrimination ellipses. Calculating the relative decrement of distinguishable colors by the digital camera in comparison with the colorimetric standard observer at different luminance factors of the optimal colors, we have found that the camera distinguishes considerably fewer very dark than very light ones, but relatively much more colors with middle lightness (Y between 40 and 70, or L* between 69.5 and 87.0). This behavior is due to the short dynamic range of the digital camera response. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 399–410, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20245
For opaque coloration systems, Kubelka-Munk turbid media theory is used commonly to model optical mixing behavior. Most educational publications on the subject use opaque paint systems when describing the two-constant approach and textile systems when describing the single-constant simplification. Because of the differences in defining concentration for these systems and the corresponding degrees of freedom, the single-constant simplification for paint and textile systems are not identical. The second edition of “Principles of Color Technology” showed a numerical example for an opaque paint system modeled using the textile equations. The third edition used the same example but modified the degrees of freedom, a hybrid of the paint and textile approaches. Recent research by Berns and Mohammadi has evaluated the single-constant simplification for modeling artist paints; they have used both the hybrid and paint approaches. Thus, it was of interest to review these different approaches and determine whether these differences have practical importance and whether future printings and editions of Principles of Color Technology should be modified. The three approaches were tested for tints made from a mixture of cobalt blue and titanium white acrylic emulsion artist paints. The differences between the textile and hybrid approaches were inconsequential. The paint approach was superior and its use is recommended for opaque paint systems. The differences in the numerical example from Principles of Color Technology were very small. For future printings of the third edition, the example will remain unchanged. For future editions, including the numerical example remains an open question. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 201–207, 2007
Digital video and display media are at a “sweet spot” of growth with brighter and more colorful digital projectors and displays available seemingly every day. Much more is possible in achieving brighter and more vibrant colors, colors that may even transcend our typical experience in terms of dynamic range and an expanded gamut in the perceptual sense. If the full capabilities of these technologies to produce a fuller visual experience are to be realized, new processing and encoding methodologies are required. In this article, the powers of adaptation and the CIECAM02 color appearance model are exploited to define perceptual gamut. The strategy of this methodology is, simply and in effect, to “push down” the white point of the display and demonstrate, both empirically and with a limited set of images, a striking gamut expansion in the perceptions of lightness, chroma, brightness, and colorfulness beyond the locus of pure, spectral color, and the MacAdam limits as observed with traditional display configurations. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 475–482, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20260
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
Microemulsion systems have proved very efficient in color removal from textile wastewater using n-butyl alcohol as cosurfactant. The cosurfactant has a very important role in microemulsified systems, as it is responsible for their stability, mainly in systems formed by ionic surfactants. Although very efficient, n-butyl alcohol is partially soluble in water, which would permit its passage to the effluent. In this work, isoamyl and octyl alcohols, due to their lower solubility in water, were used as cosurfactants to evaluate their influence in color removal. The colorimetry system used was the CIE L*a*b* (CIELAB) color space and CIE L*a*b* color difference (ΔE*ab). The wastewater used in this study was the reactive exhausted dye liquor from a dye house (first discharge) containing Procion Yellow H-E4R (CI Reactive Yellow 84), Procion Blue H-ERD (CI Reactive Blue 160) and Procion Red H-E3B (CI Reactive Red 120). The obtained results were modeled using an experimental planning (the Scheffé net) and evaluated through isoresponse diagrams by correlation graphs between experimental values and those obtained by the models with an error lower than 4%. All the optimized systems were very efficient and more than 94% of the dyes contained in the effluent were removed. The microemulsion load capacity was determined using a synthetic solution containing, the same dyes present in the reactive exhausted dyebath, but 200 times concentrated, and the dyes extraction was more than 99.6%. By comparing n-butyl, isoamyl and octyl alcohols, it was observed that the system using isoamyl alcohol presented slightly better color removal and much higher load capacity than the n-butyl and octyl alcohols. Copyright © 2004 Society of Chemical Industry
Color measurements have been performed using eighteen virgin-olive-oil tasting cups with ten different commercial virgin olive
oils, positioned in a color cabinet with a D65 source. Three geometries (spectroradiometer tilted 0°, 30°, and 60°) were employed,
simulating different positions of the taster’s eye. Our main goal was to test whether traditional blue-tinted cups effectively
conceal the color of virgin olive oils, as desired in sensorial analyses. None of the cups employed had all their geometrical
dimensions within the standardized values, despite being cups used in official sensorial analyses. Measuring a magnitude similar
to the spectral transmittance, we found substantial differences among the glasses of the eighteen tasting cups. Comparing
color variability for one virgin olive oil in different tasting cups, and one tasting cup with different virgin olive oils,
we discovered that: (1) variability was higher in the case of one virgin olive oil in different cups; (2) in both cases the
variability increased with the tilt of the spectroradiometer; (3) even when the variability was lowest (i.e., 0° measurements
for two oils in the same cup), the average color difference was above typical visual thresholds in simultaneous comparison
experiments. In the most usual case of a successive comparison between two oils in the same tasting cup, it is expected that
in most cases tasters will perceive color differences between the oils when their eyes are tilted 60° with respect to the
horizontal, but not when they observe the cup in the horizontal direction. In summary, blue-tinted olive-oil-tasting cups
reduce, but do not completely conceal, oil color. The use of opaque tasting cups with black walls is suggested.
Two psychophysical experiments were conducted to analyze the role of color attributes in simple tasks involving color matching and discrimination. In Experiment I observers made color matches using three different adjustment control methods. The results showed that the Lightness, Chroma, Hue (LCH) and the Lightness, redness/greenness, blueness/yellowness ({L, r/g, y/b}) adjustment controls elicited significantly better performance than the display RGB controls in terms of both accuracy and time, but were not significantly different from each other. Expert observers performed significantly better than naïve observers in terms of accuracy. Experiment II was a replication and extension of the experiment by Melgosa et al. [Color Res Appl 2000; 25: 356–367] in which observers judged differences and similarities for color attributes in pairs of colored patches. At a 95% confidence level, the results from judging difference were significantly better than those from judging similarity. Hue and Lightness were significantly more identifiable than Chroma, r/g, and y/b. These results indicate that people do not have ready access to the lower level color descriptors such as the common attributes used to define color spaces, and that higher level psychological processing involving cognition and language may be necessary for even apparently simple tasks involving color matching and describing color differences. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 445–457, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20257
Current color-printing technologies may use three or more inks, e.g., CMY, CMYK, CMYKcm, CMYKGO, CMYKRGB. When the number of inks exceeds three, there is the usual color-management one-to-many mapping problem. Because the spectral properties of many modern inks are optimized for maximum color gamut and in some cases, black ink may not be used for pictorial images, many prints have poor color constancy. Changes in lighting dramatically change color balance, particularly for neutrals. An algorithm was developed for multi-ink printing in which the one-to-many mapping problem was overcome by selecting ink combinations with the best color constancy between illuminants F11 and D50. The algorithm was tested using a pigmented-ink inkjet proofing printer. CMYKGO prints color-separated using this algorithm were compared with a generic ICC profile for CMYKcm prints. The CMYK inks were common to both prints. The new algorithm improved color constancy significantly.
A paired comparison psychophysical experiment was performed to evaluate the quality of several imaging techniques. Images rendered for an LCD were compared with two- and three-dimensional objects viewed in a multi- source light booth. The test images were a combination of different spectral capture and image reconstruction techniques estimating spectral reflectance factor transformed into colorimetric images by imposing an illuminant and observer, in this case simulated daylight (6800K) and incandescent (2700K) for the 1931 CIE observer. Some images were also transformed directly to colorimetry. To compare the color accuracy with conventional RGB imaging, color-managed images from a typical consumer camera were included in the experiment. All image types captured using the research-grade camera performed very well, regardless of the illuminant, number of channels, or transformation method. A set of colorimetric images captured using previously optimized filters performed as well as the multispectral images. The commercial-grade images proved to be inferior to those created with the research-grade system, as expected.
Appearance standards for gloss, haze, and goniochromatic color are applied to computer graphic reflection models. Correspondences are derived between both the gloss and haze standards and the specular exponent of the Phong model, the surface roughness of the Ward model, and the surface roughness of the Cook-Torrance model. Metallic and pearlescent colors are rendered using three aspecular measurements defined in a proposed standard for goniochromatic color. The reflection models for gloss and goniochromatic color are combined to synthesize pictures of clear coated automotive paint. Advantages of using appearance standards to select reflection model parameters include the small number of required measurements and the inexpensive commercially available instruments necessary to acquire the data. The use of a standard appearance scale also provides a more intuitive way of selecting the reflection model parameters and a reflection model independent method of specifying appearance.
This study tackles the image color to gray conversion problem. The aim was to understand the conversion qualities that can
improve the accuracy of results when the grayscale conversion is applied as a pre-processing step in the context of vision
algorithms, and in particular dense stereo matching. We evaluated many different state of the art color to grayscale conversion algorithms. We also propose an ad-hoc adaptation of the most theoretically promising algorithm,
which we call Multi-Image Decolorize (MID). This algorithm comes from an in-depth analysis of the existing conversion solutions and consists of a multi-image
extension of the algorithm by Grundland and Dodgson (The decolorize algorithm for contrast enhancing, color to grayscale conversion,
Tech. Rep. UCAM-CL-TR-649, University of Cambridge, 2005) which is based on predominant component analysis. In addition, two variants of this algorithm have been proposed and analyzed:
one with standard unsharp masking and another with a chromatic weighted unsharp masking technique (Nowak and Baraniuk in IEEE
Trans Image Process 7(7):1068–1074, 1998) which enhances the local contrast as shown in the approach by Smith etal. (Comput Graph Forum 27(2), 2008). We tested the relative performances of this conversion with respect to many other solutions, using the StereoMatcher test suite (Scharstein and Szeliski in Int J Comput Vis 47(1–3):7–42, 2002) with a variety of different datasets and different dense stereo matching algorithms. The results show that the overall performance
of the proposed MID conversion are good and the reported tests provided useful information and insights on how to design color
to gray conversion to improve matching performance. We also show some interesting secondary results such as the role of standard
unsharp masking vs. chromatic unsharp masking in improving correspondence matching.
KeywordsColor to grayscale conversion–Dense stereo matching–Dimensionality reduction–3D reconstruction–Unsharp masking
As the basic theory for color mixing in intensely light-scattering materials, the Kubelka-Munk single-constant/two-constant theories have played an important role in color science and technology. However, in practice there are some shortcomings. This paper checked the theories with a series of systematical experiments, data processing and analyzing, and has revealed several disagreements with the experimental evidence in the case of the additivity color-mixing law for turbid materials. Explanations on some of these problems are given, which are different from the conventional views.
The granite processing sector of the northwest of Spain handles many varieties of granite with specific technical and aesthetic properties that command different prices in the natural stone market. Hence, correct granite identification and classification from the outset of processing to the end-product stage optimizes the management and control of stocks of granite slabs and tiles and facilitates the operation of traceability systems. We describe a methodology for automatically identifying granite varieties by processing spectral information captured by a spectrophotometer at various stages of processing using functional machine learning techniques.
Displays are coming on the market that can produce a larger range of colors over EBU and this has led to much research on the topic of how to use the additional color gamut volume provided by the displays. Some research has focused on different methods to map colors from small to large gamuts, whereas this paper focuses on defining the required gamut boundaries for natural content. Two gamuts were created from the results of a psychophysical experiment that asked observers to choose their preferred image in terms of saturation. One gamut corresponded to the median value of their choices and the second gamut corresponded to the 90% value of their choices. The results indicated that even at the 90% value, the resulting gamut was smaller than that of the wide-gamut display for most hues and actually closer to EBU for some hues. These results are display independent, at least when considering modern displays that can reach luminance values above 250cd/m2.
The influence of surface roughness on color change in several Spanish building stones is studied in samples of the following: Red Alicante, Black Marquina, White Macael, and Yellow Triana. In an experimental laboratory test (acid attack), we simulated the weathering process and made a comparative analysis between this and the polishing process. Changes in both color and roughness were measured during these processes. In limestones with medium or high chroma (Red Alicante) and both low chroma and lightness (Black Marquina), the total color changes were particularly affected in both the polishing and acid attack processes. On the other hand, in marbles with both low chroma and high lightness (White Macael and Yellow Triana), the total color changes were almost imperceptible in both processes. However, no change occurred in the hue of any of the analyzed stones. Spectrophotometric data showed that color change was due mainly to changes in surface roughness and not to chemical reactions that may have altered the oxidation state of the chromophore in the chromogen of the stone. Contract grant sponsor: Research Project GV-97-RN-14-3 Contract grant sponsor: predoctoral research fellowship from Generalitat Valenciana awarded to D. Benavente.
"We discuss the estimation of a process capability index for three-dimensional data. Initially, we focus on the case in which the engineering tolerance associated with the measurements is a sphere. Then, we extend the discussion to the more general case in which the engineering tolerance is ellipsoidal. In both cases, we develop summary measures for repeatability and reproducibility, to be used in the context of a process capability index. In the spherical tolerance case we define summary measures, where each measure is based on the diameter of a sphere that leads to a pre-specified capture rate (we will use here 99%). As a process capability index, we propose ratios, where each ratio is the diameter of such a sphere divided by the diameter of the tolerance sphere. In the ellipsoidal tolerance case, such summary measure will be based on the length of the major axes of the ellipsoid of identical shape and orientation to the tolerance ellipsoid providing a pre-specified capture rate (again, we will use here 99%). As a process capability index, we propose ratios, where each ratio is the major axis of such ellipsoid divided by the major axis of the tolerance ellipsoid. We present two algorithms in the language R aimed at facilitating the estimation of our summary measure of variability. The first algorithm evaluates the probability that a linear combination of three (or fewer) independent chi-square variables will be less than or equal to a given constant. The second algorithm estimates the value a linear combination of chisquare variables is less than or equal to, given a pre-specified probability. In addition, we offer an algorithm in the language R for computing the process capability index in the context of color metrics. We present applications to color measurements and to R&R analysis of color metrics. We show how the components of variance in these three-dimensional measurements can be easily compared to each other and to the tolerance region, using the single-dimensional summary measures of process capability"--Abstract. Typescript. Thesis (M.S.)--Rochester Institute of Technology, 2005. Includes bibliographical references (leaves 82-82).
Industry standard methods for measuring appearance are applied to realistic image synthesis. Two appearance attributes, gloss and haze, are known to be determined by the shape of the specular reflection lobe. Standards which specify the measurement of these two geometric appearance attributes are used to select BRDF model parameters for a number of computer graphics reflection models. The bi-directional reflectance distribution function (BRDF) of metallic and pearlescent paints can be characterized with only a few industry standard specular measurements. Using these measurements, a new computer graphics BRDF model is developed. The Beard-Maxwell BRDF model, which utilizes a systematic measurement pro-tocol to determine appropriate model parameter values, is presented. An associated database containing parameters for hundreds of measured surfaces, is overviewed. Also, a new method of Monte Carlo importance sampling is described which allows impor-tance sampling of arbitrary BRDFs.
Digital cameras on the market today have a great potential to become the powerful tool for capturing images for use in all demanding fields (such as artwork digitalization), so many professionals started using digital technology. But, it is often the case, that it is necessary to spend a lot of time for visual editing and making color corrections in various software applications. In this research, some ICC color management techniques were used and tested to investigate the quicker ways to achieve digital images with improved color reproduction accuracy, without visual editing. A testing procedure for characterizing digital camera is described. This procedure is target-based, thus providing objective measurement of quality. The special color reference target for digital camera characterization was developed, applied and tested. The results show that using proposed methodology, the workflow efficiency and color accuracy can be improved.
Although metal ceramic fixed restorations are commonly preferred by clinicians, there remain a limited number of studies on how opaque porcelain color is affected by fabrication procedures, such as the number of firings and types of metal alloys.
The purpose of this study was to determine the effects of various types of metal alloys on the color of opaque porcelain after repeated firings.
Seven different types of metal ceramic alloys (3 base metals: Metalloy CC, chromium cobalt (B-MCC); Heraenium NA, nickel chromium (B-HNA); Argeloy NP, nickel chromium beryllium (B-ANP); 3 noble metals: Ceradelta, palladium silver (N-CD); Cerapall 2, palladium (N-CP2); V-Delta SF, gold palladium (N-VDSF); and 1 high noble metal: V-Gnathos Plus, gold platinum (HN-GP)) were used to support a 0.1-mm-thick layer of opaque porcelain (IPS d.SIGN Opaquer, shade B1) to determine the metal alloys' effect on the opaque porcelain color after repeated porcelain firings. Opaque porcelain was applied on specimens (16 mm x 1 mm) prepared from each type of alloy. The specimens (n=21) were subjected to 1 opaque firing, 4 consecutive dentin firing cycles, and 1 glaze firing cycle. Delta E values were calculated for all metal alloy groups from opaque firing (control group) to each subsequent firing stage within each tested alloy group. One-way ANOVA and Fisher's least significant difference tests were performed to determine the differences between alloys. In addition, DeltaE values calculated after repeated firings were analyzed by 1-way ANOVA and paired t test, to determine whether repeated dentin firing stages affected the color of opaque porcelain (alpha=.05).
After the first and second dentin firings, the color shift in opaque porcelain was significant for all tested alloy groups (P<.001). The color of opaque porcelain changed significantly after the third dentin firing for all groups except for B-HNA and N-VDSF (P<.001). After the fourth dentin firing, the color of opaque porcelain changed significantly for all tested alloy groups (P=.022 for B-ANP, P=.042 for N-VDSF, and P<.001 for remaining alloys). After glaze firing, the color change in opaque porcelain was significant in all but the N-CP2 group (P=.002 for N-VDSF, P=.014 for HN-GP, and P<.001 for remaining alloys). Delta E values showed that B-MCC after the first dentin firing, N-CD after the second dentin firing and glaze firing, and B-ANP after the third and fourth dentin firings showed significantly different DeltaE values than all remaining test alloys (P<.001).
Subsequent porcelain firings significantly affected the color of a 0.1-mm-thick layer of opaque porcelain for all alloys tested. After the third and fourth firings, 1 base metal alloy (B-ANP) showed significantly greater color change than the remaining dental alloys when the color difference was compared to baseline. In addition, the color change in a noble alloy (N-CD) was significantly less than that of the other alloys after glaze firing. However, color shifts after repeated dentin firings were imperceptible (DeltaE<2.6) and clinically acceptable (DeltaE<5.5) for each type of alloy.
There are several electronic shade-matching instruments available for clinical use, but the reliability and accuracy of these instruments have not been thoroughly investigated.
The purpose of this in vitro study was to evaluate the reliability and accuracy of 4 dental shade-matching instruments in a standardized environment.
Four shade-matching devices were tested: SpectroShade, ShadeVision, VITA Easyshade, and ShadeScan. Color measurements were made of 3 commercial shade guides (Vitapan Classical, Vitapan 3D-Master, and Chromascop). Shade tabs were placed in the middle of a gingival matrix (Shofu GUMY) with shade tabs of the same nominal shade from additional shade guides placed on both sides. Measurements were made of the central region of the shade tab positioned inside a black box. For the reliability assessment, each shade tab from each of the 3 shade guide types was measured 10 times. For the accuracy assessment, each shade tab from 10 guides of each of the 3 types evaluated was measured once. Differences in reliability and accuracy were evaluated using the Standard Normal z test (2 sided) (alpha=.05) with Bonferroni correction.
Reliability of devices was as follows: ShadeVision, 99.0%; SpectroShade, 96.9%; VITA Easyshade, 96.4%; and ShadeScan, 87.4%. A significant difference in reliability was found between ShadeVision and ShadeScan (P=.008). All other comparisons showed similar reliability. Accuracy of devices was as follows: VITA Easyshade, 92.6%; ShadeVision, 84.8%; SpectroShade, 80.2%; and ShadeScan, 66.8%. Significant differences in accuracy were found between all device pairs (P<.001) for all comparisons except for SpectroShade versus ShadeVision (P=.033).
Most devices had similar high reliability (over 96%), indicating predictable shade values from repeated measurements. However, there was more variability in accuracy among devices (67-93%), and differences in accuracy were seen with most device comparisons.
It remains unclear which gingival shade guide is most effective in producing the best visual shade match.
The purpose of this study was to determine and compare the coverage errors (CEs) of 2 different gingival shade guides and their combination in a selected population.
The CEs of the following gingival shade guides were evaluated: (1) Lucitone 199, (2) IPS Gingiva, and (3) a combination of the 2 shade guide systems. The spectral reflectance values of the center of each gingival shade tab (1.5 mm in diameter) were measured (without a backing) with a spectroradiometer and an external light source at wavelengths from 380 nm to 780 nm at 2-nm intervals. All spectral reflectance measurements were made using 0-degree observer and 45-degree illumination and then converted to CIE values. The attached gingiva of 120 subjects was measured with the same protocol. The CEs of each of the 120 subjects' attached gingiva for each of the 2 shade guide systems and their combination were determined and averaged. The mean minimum CEs were analyzed with repeated measures ANOVA and the post hoc Tukey HSD for multiple comparison (alpha=.05).
A significant difference (P<.001) was found among the mean minimum CEs of the 2 gingival shade guide systems and their combination. The Tukey HSD test revealed that the mean minimum CEs for Lucitone 199 (Delta E 10.8 +/-4.4) were significantly different from the IPS Gingiva (Delta E 8.6 +/-3.6) shade guide system. However, the combination of the 2 gingival shade guide systems (Delta E 7.9 +/-3.4) was not significantly different from the IPS Gingiva system, but a significant difference was found among races (P=.016). No interactions were found between the other tested groups. The mean CE for white individuals (Delta E 8.3 +/-2.5) is significantly different and less than the mean CE for African Americans (Delta E 10.0 +/-4.4). The CEs for Asians (Delta E=9.1 +/-4.3) and others (Delta E 9.0 +/-4.4) are not significantly different from CEs for whites or African Americans.
The IPS Gingiva shade guide system resulted in the lowest CEs compared to the Lucitone 199 shade guide system. The mean CE for Lucitone 199 was significantly greater than the mean CE for IPS Gingiva and for the combination of the 2 guides. The mean CE for whites is significantly different and less than the mean CE for African Americans. The CEs for Asians and others are not significantly different from CEs for whites or African Americans.
The total quantifiable color difference between shade matching and shade duplication has not been investigated formally.
The purpose of this in vitro study was to evaluate and compare the color difference of the total color replication process and the direction of the individual color parameters for 3 dental porcelain shade-matching systems.
The shade of 11 porcelain master disks was determined visually and instrumentally using 3 porcelain shade-matching systems: (1) Vita Lumin/Vita VMK 68, (2) Vitapan 3D-Master/Vita Omega 900, and (3) Shofu ShadeEye-EX/Vintage Halo. Corresponding porcelain disks made of 4.5 mm opaque and 1 mm dentin porcelain were fabricated with each of the porcelain systems. The colors of the master disks and fabricated disks (CIE L* a* b* coordinates) were measured with a spectroradiometer with a 45 degrees /0 degrees configuration. Repeated-measures analysis of variance was used to evaluate within-group differences among the porcelain systems for the total color difference (Delta E) and direction of the color parameters (Delta L, Delta a, and Delta b). The Ryan-Einot-Gabriel-Welsch multiple range test was used for post-hoc analysis (alpha=.05).
The largest mean Delta E was recorded for the Vitapan 3D-Master system, which was significantly different from the other systems (P=.0024). A significant difference was found between the interaction of the different systems and the direction of color (P=.0024). The amount of change within each color parameter was dependent on the porcelain system, as well as the amount of change among the color parameters.
Within the limitations of this study, the results suggest that reliable delivery of a properly matched restoration to existing porcelain restorations cannot be ensured regardless of the shade assessment method used (visual or computer-generated).
The past decade or so has witnessed a marked increase in consumer awareness in virtually every aspect of modern life. The concomitant rise in consumer expectations has extended, of course, to dentistry and, in particular, to the more aesthetic aspects of the discipline, namely shade matching and tooth whiteness. As a consequence, various instrumental methods of shade matching have been launched commercially in recent years; in addition, considerable, commercial research effort is currently being focused on instrumental methods of assessing tooth 'whitening'. Such interest in 'aesthetic dentistry' has, in turn, resulted in the author's laboratories having received myriad enquiries from dental researchers in relation to colour perception, colour theory and instrumental colour measurement. Despite the importance of colour in relation to dentistry and the current, very high level of research interest in the subject, remarkably few, if any, references have appeared that concern the application of colour theory to dentistry; furthermore, the colorimetric aspects of shade matching and tooth whitening have received virtually no discussion in relevant journals. The high level of interest in colour in dentistry coupled with the paucity of publications in this particular area, prompted the research work presented here.
This study tested the shade match of single porcelain-fused-to-metal restorations with the adjacent dentition when the restorations were fabricated according to data from conventional visual shade matching or from a new spectrophotometric system. The samples of a Vita Classic shade guide were measured with the spectrophotometer to determine the CIE L*a*b* color parameters. Three clinicians independently selected the best match to a maxillary right or left incisor needing a restoration in 10 patients. The 10 incisors were then measured using a reflectance spectrophotometer. CIE L*a*b* coordinates were directly recorded on the spectrophotometer's detector area using a standard light source. Resulting conventional and spectrophotometric restorations were tested intraorally for best match with the adjacent incisor using conventional shade matching versus spectrophotometric measuring. Total color difference was calculated, and all groups were statistically analyzed. Initial shade evaluation matched for all three visual shade selections in two cases. In six cases only two evaluators matched, and in the remaining two cases all three visual selections differed. In contrast, in nine of 10 cases all three spectrophotometric shade selections matched. Additionally, in nine of 10 cases delta E values of visually assessed tooth shades were higher than spectrophotometrically assessed delta E values. Resulting delta E values for conventional crowns compared to spectrophotometric crowns were significantly higher. Finally, in nine of 10 cases spectrophotometric crowns were preferred over conventional crowns for definitive cementation when evaluated visually. Spectrophotometric shade analysis and communication can be used efficiently for fabrication of porcelain-fused-to-metal restorations.
This paper presents empirical support for a new observer model of inferring three-dimensional shape from monocular texture cues. By measuring observers’ abilities to estimate the relative three-dimensional curvature along a textured surface from two-dimensional projected images, and concurrently examining the local spectral changes occurring in the projected image for various texture patterns, we have found that correlated changes in oriented energy along lines corresponding to the lines of maximum and minimum curvature of the surface are crucial for conveying the three-dimensional shape of the surface. Energy along these lines of maximum and minimum curvature can be used to compute the orientation of local surface patches. Texture patterns consisting of simple and complex sinusoidal gratings and plaids, and filtered noise were drawn onto a surface that was corrugated sinusoidally in depth about the horizontal axis and projected in perspective onto an image plane. The perceived relative surface curvature was reconstructed from measurements of local ordinal depth around a central fixation point at 12 different phases of the corrugation. Our results show that: (1) it is neither necessary nor sufficient to identify individual texture elements or texture gradients in order to extract the shape of the surface; (2) one-dimensional frequency modulation is insufficient for conveying complex three-dimensional shape. (3) Veridical ordinal depth is seen only when the projected pattern contains changes in oriented energy along lines corresponding to projected lines of maximum curvature of the surface. (4) For a surface corrugated in depth about the horizontal axis, this pattern of oriented energy arises from energy along the vertical direction in the global Fourier transform of the pre-corrugated pattern. (5) Local orientation changes across lines of minimum curvature can be also critical for conveying shape. (6) These correlated orientation changes along lines of maximum and minimum curvature are entirely lost in parallel projection. Hence texture is a useful cue for shape if the image is a perspective projection. (7) Only some natural textures will provide sufficient monocular cues to support veridical shape inferences, and this can be predicted from their global Fourier transforms.
We have measured color discrimination in the isoluminant plane under rigorously controlled adaptation conditions. Two regimes were studied. Under the first regime the observer was adapted to the region of color space in which the discriminations were made. Thresholds for detecting changes along the S-(L + M) axis are a linearly increasing function of the excitation of the S cones. Thresholds for detecting changes along the L-M axis are independent of the locus of adaptation along this axis. The straightness of these functions is inconsistent with the theory that second stage mechanisms are more sensitive in the middle of their operating ranges. No convincing evidence of interactions in the effects of adaptation locus or test stimuli was observed. Under the second regime the observer was adapted to one point in color space and the stimuli to be discriminated were located in other places in color space. Discrimination seems to be limited primarily by mechanisms maximally sensitive to modulation along the isoluminant cardinal axes but evidence suggestive of the operation of higher order mechanisms was also found.
We measured the responses of 305 neurons in striate cortex to moving sinusoidal gratings modulated in chromaticity and luminance about a fixed white point. Stimuli were represented in a 3-dimensional color space defined by 2 chromatic axes and a third along which luminance varied. With rare exceptions the chromatic properties of cortical neurons were well described by a linear model in which the response of a cell is proportional to the sum (for complex cells, the rectified sum) of the signals from the 3 classes of cones. For each cell there is a vector passing through the white point along which modulation gives rise to a maximal response. The elevation (theta m) and azimuth (phi m) of this vector fully describe the chromatic properties of the cell. The linear model also describes neurons in l.g.n. (Derrington et al., 1984), so most neurons in striate cortex have the same chromatic selectivity as do neurons in l.g.n. However, the distributions of preferred vectors differed in cortex and l.g.n.: Most cortical neurons preferred modulation along vectors lying close to the achromatic axis and those showing overt chromatic opponency did not fall into the clearly defined chromatic groups seen in l.g.n. The neurons most responsive to chromatic modulation (found mainly in layers IVA, IVC beta, and VI) had poor orientation selectivity, and responded to chromatic modulation of a spatially uniform field at least as well as they did to any grating. We encountered neurons with band-pass spatial selectivity for chromatically modulated stimuli in layers II/III and VI. Most had complex receptive fields. Neurons in layer II/III did not fall into distinct groups according to their chromatic sensitivities, and the chromatic properties of neurons known to lie within regions rich in cytochrome oxidase appeared no different from those of neurons in the interstices. Six neurons, all of which resembled simple cells, showed unusually sharp chromatic selectivity.
A new method of measuring simultaneous contrast, or chromatic induction, is introduced and used to test the hypotheses that induction results from either multiplicative or subtractive interaction of either (1) like receptors or (2) like second-stage, opponent mechanisms. Predictions derived from these hypotheses do not predict the outcome of the experiments as well as the traditional notion that induced colors are in the direction complementary to the inducing color with respect to the test color. We conclude that simultaneous contrast is a consequence of interaction within higher-level chromatic mechanisms.
For a given pair of colors (i) and (j) of the same brightness, an observer generates in a visual colorimeter a third color (i,j) such that he perceives all three colors to be equally bright and the three differences between them to be of equal size. In color-perception space, the three colors form an equilateral triangle on a surface of constant brightness. The precision of setting the third color (i,j) can be characterized by ellipsoids in color space. Three observers take part in the experiment and over 30 pairs of colors (i) and (j) are presented to them. In approximately 50% of the cases a given observer will agree, within the uncertainty of his own data, with the mean color (i,j) of another observer. The corresponding color-difference-matching ellipses (cross sections of the ellipsoids) of the different observers show a satisfactory correlation. The experimental data presented may be used to test color-difference formulas and the chromaticity spacing in UCS diagrams.
Evidence is presented for a visual capacity specialized to sense the chromatic direction of change in colors over time. Discrimination thresholds were measured between pairs of suprathreshold color changes presented in consecutive intervals. In one interval, the color of a spatially uniform disk was changed at a constant speed along the circumference of a circle in an equiluminant color plane. In the other, an instantaneous change, which can be described as a vector in the equiluminant plane, was added to the circular color modulation. Averaging across conditions showed that the threshold for discriminating between a pair of purely temporal color changes was approximately proportional to the cosine of the color angle between them. The model that is presented to account for these results is based on parallel directional-color mechanisms that are tuned to different directions in color-space and are responsive to change in one color direction but not its opposite.
Our initial purpose was to develop a quantitative method of estimating the cardinal directions of color space. The method is based on the finding that patterns consisting of pairs of drifting gratings modulated along different cardinal axes appear to slip with respect to one another, while the same patterns appear as a single coherent plaid if the modulation directions of the patterns are rotated by 45 deg in color space [Krauskopf & Farell (1990). Nature, 348,328-331]. A forced-choice procedure was used in which observers were asked to choose which of two successively presented patterns appeared less coherent. The patterns consisted of pairs of drifting gratings; the direction of modulation of one of the gratings was fixed and that of the other varied. For example, an estimate of an individual's isoluminant plane could be obtained by fixing the modulation of one grating in the luminance direction and finding the elevation of the modulation of the other grating that resulted in minimum perceived coherence. We found it important to take into consideration individual differences in the tilt of the isoluminant plane in color space and in the detectability of targets in the nominal cardinal directions. When this was done we found that reliable measurements could be made. The method effectively provided quantitative estimates of the cardinal directions. However, the most important result was the inadequacy of the generalization that patterns appear coherent when they share similar components along cardinal directions (Krauskopf & Farell, 1990) to account for the new results. The present results suggest that patterns appear not to cohere to the extent that they fail to stimulate common chromatic mechanisms, but the assumption that these mechanisms are tuned only along cardinal axes can be rejected. Along with other data the results point to the existence of higher-order mechanisms tuned to different isoluminant chromatic directions.
This paper examines the nature of the post-receptoral chromatic and achromatic mechanisms involved in a texture segmentation task. Observers viewed a 64 x 64 square-element texture in which the chromaticity and brightness of each element was drawn from a one-dimensional Gaussian distribution of values centered at a white point in color space. The orientation in color space and variance of this distribution defined the noise in the stimulus. The mean chromaticity and/or brightness of a central 32 x 32 element area (the target) was shifted away from the white point along the same direction as the noise or along a different direction. We measured target thresholds as a function of noise amplitude. The steepness of this relationship defined the effectiveness of the noise. Within planes spanned by the achromatic axis and one of the two cardinal chromatic axes, we found selective effects of noise along each of the two cardinal axes. Within the purely chromatic (isoluminant) plane, we found selective effects of noise along four lines--the two cardinal chromatic axes and two intermediate ones. We describe a simple model to account for our results.
We investigated the functional properties of neurons in extrastriate area V3. V3 receives inputs from both magno- and parvocellular pathways and has prominent projections to both the middle temporal area (area MT) and V4. It may therefore represent an important site for integration and transformation of visual signals. We recorded the activity of single units representing the central 10 degrees in anesthetized, paralyzed macaque monkeys. We measured each cell's spatial, temporal, chromatic, and motion properties with the use of a variety of stimuli. Results were compared with measurements made in V2 neurons at similar eccentricities. Similar to area V2, most of the neurons in our sample (80%) were orientation selective, and the distribution of orientation bandwidths was similar to that found in V2. Neurons in V3 preferred lower spatial and higher temporal frequencies than V2 neurons. Contrast thresholds of V3 neurons were extremely low. Achromatic contrast sensitivity was much higher than in V2, and similar to that found in MT. About 40% of all neurons showed strong directional selectivity. We did not find strongly directional cells in layer 4 of V3, the layer in which the bulk of V1 and V2 inputs terminate. This property seems to be developed within area V3. An analysis of the responses of directionally selective cells to plaid patterns showed that in area V3, as in MT and unlike in V1 and V2, there exist cells sensitive to the motion of the plaid pattern rather than to that of the components. The exact proportion of cells classified as being selective to color depended to a large degree on the experiment and on the criteria used for classification. With the use of the same conditions as in a previous study of V2 cells, we found as many (54%) color-selective cells as in V2 (50%). Furthermore, the responses of V3 cells to colored sinusoidal gratings were well described by a linear combination of cone inputs. The two subpopulations of cells responsive to color and to motion overlapped to a large extent, and we found a significant proportion of cells that gave reliable and directional responses to drifting isoluminant gratings. Our results show that there is a significant interaction between color and motion processing in area V3, and that V3 cells exhibit the more complex motion properties typically observed at later stages of visual processing.
Orientation tuning of neurons is one of the chief emergent characteristics of the primary visual cortex, V1. Neurons of the lateral geniculate nucleus, which comprise the thalamic input to V1, are not orientation-tuned, but the majority of V1 neurons are quite selective. How orientation tuning arises within V1 is still controversial. To study this problem, we measured how the orientation tuning of neurons evolves with time using a new method: reverse correlation in the orientation domain. Orientation tuning develops after a delay of 30-45 milliseconds and persists for 40-85 ms. Neurons in layers 4C alpha or 4C beta, which receive direct input from the thalamus, show a single orientation preference which remains unchanged throughout the response period. In contrast, the preferred orientations of output layer neurons (in layers 2, 3, 4B, 5 or 6) usually change with time, and in many cases the orientation tuning may have more than one peak. This difference in dynamics is accompanied by a change in the sharpness of orientation tuning; cells in the input layers are more broadly tuned than cells in the output layers. Many of these observed properties of output layer neurons cannot be explained by simple feedforward models, whereas they arise naturally in feedback networks. Our results indicate that V1 is more than a bank of static oriented filters; the dynamics of output layer cells appear to be shaped by intracortical feedback.
The problem of color constancy may be solved if we can recover the physical properties of illuminants and surfaces from photosensor responses. We consider this problem within the framework of Bayesian decision theory. First, we model the relation among illuminants, surfaces, and photosensor responses. Second, we construct prior distributions that describe the probability that particular illuminants and surfaces exist in the world. Given a set of photosensor responses, we can then use Bayes’s rule to compute the posterior distribution for the illuminants and the surfaces in the scene. There are two widely used methods for obtaining a single best estimate from a posterior distribution. These are maximum a posteriori (MAP) and minimum mean-squared-error (MMSE) estimation. We argue that neither is appropriate for perception problems. We describe a new estimator, which we call the maximum local mass (MLM) estimate, that integrates local probability density. The new method uses an optimality criterion that is appropriate for perception tasks: It finds the most probable approximately correct answer. For the case of low observation noise, we provide an efficient approximation. We develop the MLM estimator for the color-constancy problem in which flat matte surfaces are uniformly illuminated. In simulations we show that the MLM method performs better than the MAP estimator and better than a number of standard color-constancy algorithms. We note conditions under which even the optimal estimator produces poor estimates: when the spectral properties of the surfaces in the scene are biased.
For a visual system to possess color constancy across varying illumination, chromatic signals from a scene must remain constant at some neural stage. We found that photoreceptor and opponent-color signals from a large sample of natural and man-made objects under one kind of natural daylight were almost perfectly correlated with the signals from those objects under every other spectrally different phase of daylight. Consequently, in scenes consisting of many objects, the effect of illumination changes on specific color mechanisms can be simulated by shifting all chromaticities by an additive or multiplicative constant along a theoretical axis. When the effect of the illuminant change was restricted to specific color mechanisms, thresholds for detecting a change in the colors in a scene were significantly elevated in the presence of spatial variations along the same chromatic axis as the simulated chromaticity shift. In a variegated scene, correlations between spatially local chromatic signals across illuminants, and the desensitization caused by eye movements across spatial variations, help the visual system to attenuate the perceptual effects that are due to changes in illumination.
We recorded from single cells in area V2 of cynomolgus monkeys using standard acute recording techniques. After measuring each cell's spatial and temporal properties, we performed several tests of its chromatic properties using sine-wave gratings modulated around a mean gray background. Most cells behaved like neurons in area V1 and their responses were adequately described by a model that assumes a linear combination of cone signals. Unlike in V1, we found a subpopulation of cells whose activity was increased or inhibited by stimuli within a narrow range of color combinations. No particular color directions were preferentially represented. V2 cells showing color specificity, including cells showing narrow chromatic tuning, were present in any of the stripe compartments, as defined by cytochrome-oxidase (CO) staining. An addition of chromatic contrast facilitated the responses of most neurons to gratings with various luminance contrasts. Neurons in all three CO compartments gave significant responses to isoluminant gratings. Receptive-field properties of cells were generally similar for luminance and chromatically defined stimuli. We found only a small number of cells with a clearly identifiable double-opponent receptive-field organization.
Colored targets pop out of displays under conditions in which the standard red-green, yellow-blue and black-white mechanisms cannot directly mediate detection. Experimental evidence suggests that observers possess chromatic detection mechanisms tuned to intermediate hues such as orange as well as to hues characterizing the standard color-opponent mechanisms and that these mechanisms, as a group, form a fine-grained representation of hue within the central visual field. Spatially-parallel search is mediated by a single such mechanism that is spectrally sensitive to the target chromaticity but insensitive to the distractor chromaticities; different mechanisms are used to detect a single target in a way that depends on distractor chromaticities.
Current models of colour vision assume that colour is represented by activity in three independent post-receptoral channels: two encoding chromatic information and one encoding luminance. An important feature of these models is that variations in certain directions in colour space modulate the response of only one of the channels. We have tested whether such models can predict how colour appearance is altered by adaptation-induced changes in post-receptoral sensitivity. In contrast to the changes predicted by three independent channels, colour appearance is always distorted away from the direction in colour space to which the observer has adapted. This suggests that at the level at which the adaptation effects occur, there is no colour direction that invariably isolates only a single post-receptoral channel.
Evidence supporting the existence of higher order color mechanisms, that is, ones beyond the previously identified second stage mechanisms is presented. This evidence includes a reanalysis of the data of Krauskopf et al. [Vision Res. 20, 1123-1131 (1982)] on the desensitizing effects of viewing chromatically modulated fields, new experiments on a generalized version of the "transient tritanopia" experiment of Mollon and Polden [Phil. Trans. R. Soc. Lond. 278, 207-240 (1977)] and results on the relationship between discrimination and detection of brief color changes.
Viewing of annuli modulated in color in a sawtooth fashion in time results in differential threshold elevations for the detection of color changes of inscribed disks. The elevations are of nearly the same magnitude as those resulting from viewing modulated disks. However, the differential effects on thresholds for complimentary colors are reversed. The differential effects, thus, are correlated with the variation in appearance of the test area.
This paper introduces a new technique for the analysis of the chromatic properties of neurones, and applies it to cells in the lateral geniculate nucleus (l.g.n.) of macaque. The method exploits the fact that for any cell that combines linearly the signals from cones there is a restricted set of lights to which it is equally sensitive, and whose members can be exchanged for one another without evoking a response. Stimuli are represented in a three-dimensional space defined by an axis along which only luminance varies, without change in chromaticity, a 'constant B' axis along which chromaticity varies without changing the excitation of blue-sensitive (B) cones, a 'constant R & G' axis along which chromaticity varies without change in the excitation of red-sensitive (R) or green-sensitive (G) cones. The orthogonal axes intersect at a white point. The isoluminant plane defined by the intersection of the 'constant B' and 'constant R & G' axes contains lights that vary only in chromaticity. In polar coordinates the constant B axis is assigned the azimuth 0-180 deg, and the constant R & G axis the azimuth 90-270 deg. Luminance is expressed as elevation above or below the isoluminant plane (-90 to +90 deg). For any cell that combines cone signals linearly, there is one plane in this space, passing through the white point, that contains all lights that can be exchanged silently. The position of this 'null plane' provides the 'signature' of the cell, and is specified by its azimuth (the direction in which it intersects the isoluminant plane of the stimulus space) and its elevation (its angle of inclination to the isoluminant plane). A colour television receiver was used to produce sinusoidal gratings whose chromaticity and luminance could be modulated along any vector passing through the white point in the space described. The spatial and temporal frequencies of modulation could be varied over a large range. When stimulated by patterns of low spatial and low temporal frequency, two groups of cells in the parvocellular laminae of the l.g.n. were distinguished by the locations of their null planes. The null planes of the larger group were narrowly distributed about an azimuth of 92.6 deg and more broadly about an elevation of 51.5 deg, which suggests that they receive opposed, but not equally balanced, inputs from only R and G cones. These we call R-G cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Thresholds for detecting changes in color are raised following viewing a field sinusoidally modulated in color over time. This effect is highly selective. For example, thresholds for detecting reddish and greenish changes from white are raised following viewing a field varying in a reddish-greenish direction, but not after viewing one varying in a yellowish-bluish direction. Similarly thresholds for yellowish and bluish changes from white are raised following viewing a field varying along a yellowish-bluish axis but not altered by exposure to reddish-greenish variation. Thresholds for chromatic changes are not raised following viewing a field varying in luminance. Thresholds for changes in luminance are raised following viewing a field varying in luminance but not altered by exposure to purely chromatic variation. Since this selectivity is found only for these directions and not intermediate directions in color space we conclude that these directions are cardinal, that is, signals varying along these directions are carried along separate, fatiguable, second stage pathways. The results conform to the expectations of opponent process theory with the important exception that the yellowish-bluish cardinal direction is a tritanopic confusion line and not a red-green equilibrium line.
Color contrast was assessed in the equiluminant plane using asymmetric matching. Test and surround stimuli lay on cardinal axes of a cone opponent chromaticity space, (l-lw, s-sw). Matches were made as a function of both test and surround chromaticity. Some matches showed constant maximal induction consistent with retinal adaptation to the surround; others showed constant minimal induction. These matches were separated by a hiatus in which color appearance did not vary greatly with test chromaticity. The results suggest that rectified retinal spectral opponent pathways do not form a unitary chromatic opponent pathway but are subject to pathway-specific interactions.
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