Wood photography using light irradiation and heat treatment

To apply the coloring method using light irradiation and thermal treatment to print photographs on wood, the effect of the transmittance of negative films was investigated. ΔE* decreased with light irradiation when specimens covered with films with transmittances exceeding 20% were irradiated for 100 h. It was thought that this phenomenon was due to the decrease in Δb*. The color of light‐irradiated wood changed remarkably with thermal treatment; however, the change in the color of exposed specimens covered with films with transmittances exceeding roughly 20% became constant. Clear photographs could be printed on wood using negative films with transmittances less than approximately 20%. Furthermore, the difference between the maximum and minimum values of ΔE* after thermal treatment was about 22. Humans can distinguish four to seven colors that can be created by this method. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 312–316, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20027     

Evaluating the 1931 CIE color‐matching functions

The use of colorimetry within industry has grown extensively in the last few decades. Central to many of today's instruments is the CIE system, established in 1931. Many have questioned the validity of the assumptions made by Wright¹ and Guild,² some suggesting that the 1931 color‐matching functions are not the best representation of the human visual system's cone responses. A computational analysis was performed using metameric data to evaluate the CIE 1931 color‐matching functions as compared to with other responsivity functions. The underlying assumption was that an optimal set of responsivity functions would yield minimal color‐difference error between pairs of visually matched metamers. The difference of average color differences found in the six chosen sets of responsivity functions was small. The CIE 1931 2° color‐matching functions on average yielded the largest color difference, 4.56 ΔE. The best performance came from the CIE 1964 10° color‐matching functions, which yielded an average color difference of 4.02 ΔE. An optimization was then performed to derive a new set of color‐matching functions that were visually matched using metameric pairs of spectral data. If all pairs were to be optimized to globally minimize the average color difference, it is expected that this would produce an optimal set of responsivity functions. The optimum solution was to use a weighted combination of each set of responsivity functions. The optimized set, called the Shaw and Fairchild responsivity functions, was able to reduce the average color difference to 3.92 ΔE. In the final part of this study a computer‐based simulation of the color differences between the sets of responsivity functions was built. This simulation allowed a user to load a spectral radiance or a spectral reflectance data file and display the tristimulus match predicted by each of the seven sets of responsivity functions. © 2002 Wiley Periodicals, Inc. Col Res Appl, 27, 316–329, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10077     

Are chroma tolerances dependent on hue‐angle?

Relationships between suprathreshold chroma tolerances and CIELAB hue‐angles have been analyzed through the results of a new pair‐comparison experiment and the experimental combined data set employed by CIE TC 1–47 for the development of the latest CIE color‐difference formula, CIEDE2000. Chroma tolerances have been measured by 12 normal observers at 21 CRT‐generated color centers L*₁₀ = 40, C*_ab,10 = 20 and 40, and h_ab,10 at 30° regular steps). The results of this experiment lead to a chroma‐difference weighting function with hue‐angle dependence W_CH, which is in good agreement with the one proposed by the LCD color‐difference formula [Color Res Appl 2001;26:369–375]. This W_CH function is also consistent with the experimental results provided by the combined data set employed by CIE TC 1–47. For the whole CIE TC 1–47 data set, as well as for each one of its four independent subsets, the PF/3 performance factor [Color Res Appl 1999;24:331–343] was improved by adding to CIEDE2000 the W_CH function proposed by LCD, or the one derived by us using the results of our current experiment together with the combined data set employed by CIE TC 1–47. Nevertheless, unfortunately, from the current data, this PF/3 improvement is small (and statistically nonsignificant): 0.3 for the 3657 pairs provided by CIE TC 1–47 combined data set and 1.6 for a subset of 590 chromatic pairs (C*_ab,10>5.0) with color differences lower than 5.0 CIELAB units and due mainly to chroma. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 420–427, 2004; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/col.20057     

Use of gray system theory in product‐color planning

A quantitative evaluation method for the CIE color‐planning activity within the product design cycle is proposed in this article. The questionnaire‐based process that is traditionally employed to obtain objective color psychology tends to be time‐consuming. Accordingly, this study proposes the use of gray system theory to overcome this problem. In the CIE color system, colors are defined by three primary colors, R (red), G (green), and B (blue). Using these three principal hues with fixed equigap sequences to simulate specific basic color samples is an efficient means of investigating unicolor images on a personal computer. However, a gray relational generating operation can be used to simulate colors beyond these basic samples and to predict the corresponding membership values for semantic words. In addition, the gray clustering operation is introduced to predict the overall color image evaluation of multicolored products. The predicted evaluation results of the gray system theory and a back‐propagation neural network are both compared with experimentally verified results. The results indicate that the gray forecasting model is the more effective means of predicting the image evaluation, and therefore, the method is adopted within the color‐planning activity. Although this study takes the example of the Internet‐aided color planning of a baby walker as a case study, the proposed method can also be used on other products. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 222–231, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20009     

How the CIE 1931 color-matching functions were derived from Wright-Guild data

The principles that guided the founders of the CIE 1931 system for colorimetry are examined. The principles are applied to the Wright-Guild experimental determinations of the color mixture data to show in detail how and why each step in the development of the CIE 1931 system for colorimetry came about. These steps are examined in the light of 65 years advanced knowledge of colorimetry. The necessity for each of these principles in the modern world is examined critically to determine whether one might hold to the same principles if the system were being freshly formulated today. © 1997 John Wiley & Sons, Inc. Col Res Appl, 22, 11–23, 1997.     

Theoretical aspects of mesopic photometry and their implication in data assessment and investigation planning

There is no photometric standard observer for the mesopic region, but five systems of mesopic photometry have been proposed, each based on its own experimental data set. But more experimental data are required, especially for parts of the colour gamut. In order to make the best use of existing data and to optimize the value of new data, theoretical aspects need to be considered. These lead to the conclusion that not all data are acceptable. © 1998 John Wiley & Sons, Inc. Col Res Appl, 23, 264–273, 1998     

Improvement of CMC upon CIEDE2000 for a new experimental dataset

This communication reports additional analyses of the dataset presented in the article “A preliminary comparison of CIE color differences to textile color acceptability using average observers” by Mangine, Jakes, and Noel © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 239–241, 2006     

Color assessment of granitic rocks and implications for their ornamental utilization

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*_abh_ab 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     

Analysis of five sets of color difference data

In a systematic optimization process five sets of recent color difference data have been analyzed for commonalities. Adjustment of the X tristimulus values and application of a systematic, surround dependent S_L function was found to be beneficial in all cases. Other modifications of the CIE94 color‐difference formula were found to bring improvements only in some cases and may be spurious. Application of what seem to be nonsystematic scale factors in a range of 0.78–1.38 improve correlation between calculated and visual color differences in all cases. After optimization, calculated color difference values explain between 80–90% of the variation in visual color differences. Some of the datasets are shown not to be well suited for formula optimization. Optimization in all cases by set, for three sets of data by quadrant in the a^*b^* diagram, and for one set by subset did not reveal any additional systematic trends for improvement. It appears that the basic structure of CIE94, with the recommended modifications, is a good approximation as a model for color‐difference evaluation in the range from 0.5–10 units of difference. The model is surround dependent. A number of issues remain to be resolved. © 2001 John Wiley & Sons, Inc. Col Res Appl, 26, 141–150, 2001     

Diffractive CIE 1931 chromaticity diagram

A novel diffractive CIE 1931 chromaticity diagram is generated by utilizing surface relief gratings on a plastic sample. A properly illuminated sample is shown to reflect the CIE chromaticity diagram with exact colors and large gamut. Additive color mixing is accomplished by utilizing the four main peaks of a 4000 K fluorescent lamp's spectrum as the primary colors. The primary grating units are reflecting the combination of the primary colors to the desired viewing angle and thereby forming the correct chromaticity (x, y) at each pixel of chromaticity diagram. Weights of primary colors at each pixel of the diagram are controlled by fixing the relative areas of the primary gratings. The master grating is fabricated with aid of electron beam lithography. The final grating is hot embossed on a polycarbonate sample using an electroplated nickel shim. Chromaticity values are measured from the plastic sample by a spectroradiometer. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 409–413, 2007     

Transformation of primaries using four chromaticity points and their maps

This note describes several approaches to transforming primaries using four chromaticity points and their maps. The motivation is an exercise described by Wold (Die Farbe 1999/2000;45:99–117). Whereas, several approaches to the problem depend on the points corresponding to the primaries themselves, and on whether the old primaries are specified in the new system or vice versa. This note presents an approach that will work for a general (nonsingular) set of four reference chromaticity points and their maps. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 506–509, 2008     

Derivation of the 1964 colorimetric standards

Although the CIE states that the 1931 2° [x (λ), y (λ), z (λ)] standard observer characteristics and those of the 1964 10° [x ₁₀(λ), y ₁₀(λ), z ₁₀(λ)] standard observer were derived from experimental data in the same way, there are differences. One discrepancy is a difference of 6 nm in the tangent wavelength of the (Y)(Z) line on the chromaticity chart, with a corresponding change in the minimum wavelength of x ₁₀. The reason for this is investigated and the two systems are considered. © 1998 John Wiley & Sons, Inc. Col Res Appl, 23, 221–225, 1998     

Request for existing experimental datasets on color differences

The Technical Committee 1‐55 of the International Commission on Illumination on “Uniform color space for industrial color difference evaluation” is requesting the submission of datasets for use in developing a new approximately uniform color space for industrial use. The data should be submitted to the TC Chair, Dr. Manuel Melgosa at the University of Granada. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 159, 2007     

Colour matching using LEDs as primaries

In our metameric experiment, the colour of a filtered incandescent lamp was matched with the additive mixture of three LEDs in a Lummer–Brodhun‐type visual photometer. Two sets of primaries were used, one had their dominant wavelengths at 467, 533, and 600 nm; the other set had dominant wavelengths at 478, 552, and 635 nm. These values correspond approximately to the characteristic wavelengths of the Prime and Non‐Prime Colour spectral regions defined by W. A. Thornton. 1 Both the light of the incandescent lamp and that of the LED clusters were seen monocularly in a centrally divided bipartite field at a visual angle of 2°. The luminance of the matching fields was in the order of 20 cd/m² to provide sufficient gamut for the LED mixture. Ten young observers with normal colour vision participated in the experiment. The emission spectra of the viewing fields were measured with an array‐type spectroradiometer, and two sets of colour‐matching functions were used to calculate the chromaticity of the matching stimuli: the CIE 1931 standard colorimetric observer and the Judd–Vos modification of the colour‐matching functions. We found that the Judd–Vos modification of the CIE 1931 standard observer represents more accurately the real observers in the evaluation of our results. No systematic differences between the use of the two sets of LEDs were detected in contradiction to Thornton's findings. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 360–364, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20044     

Transformation from Munsell space to Swedish NCS—Through Nayatani theoretical space

A relationship and a method of transformation are given on color attributes between Munsell, Nayatani Theoretical, and NCS color spaces. The purpose of the study is to clarify the conceptual differences in structure between the three spaces. The structural differences are explained by using the transformations on five color samples. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 151–157, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10235     

Correlation and modeling between color variation and quality of the surface between accelerated and natural tropical weathering in Acacia mangium,Cedrela odorata and Tectona grandis wood with two coating

To prevent the photodegradation process, a wide range of coatings have been developed. This study evaluated wood color change (ΔE*) and the surface quality index (SQI) generated by ASTM D‐660 standards in wood protected with polyurethane and varnish finishes of three tropical species (Acacia mangium, Cedrela odorata and Tectona grandis) in two weathering conditions (natural and accelerated condition). In addition, a model was developed to predict ΔE* and SQI in natural weathering based on ΔE* and SQI from accelerated weathering. The results showed that the application of these finishes generated variations in the color parameters of wood before being exposed to the elements. Additionally, it was found that finishes generated increases in ΔE*, especially the varnish type finish, and decreasing of SQI. Finally, models were found to predict color changes or surface quality in natural weathering based on color changes or surface quality in accelerated weathering. The model algorithm was expressed by ΔE* or SQI measured (X) and time exposure (t) in accelerated weathering by equation . With these models, it is possible to predict the equivalence of exposure times in natural weathering in tropical conditions for different kinds of finishes in three tropical species. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 519–529, 2014     

Metamers for assessing the quality of CIE D50 simulators

Simulators of CIE Illuminants D65 and D75 are widely used for visually judging colors, but D50 simulators are used in photography and color printing. The CIE method of assessing the quality of daylight simulators provides sets of virtual metamers for assessing D55, D65, and D75 simulators, but does not provide them for D50. Data specifying sets of metamers for assessing the quality of D50 simulators are presented. They are based in part on data in a Japanese standard and in part on newly derived data. © 1996 John Wiley & Sons, Inc.     

Deriving instrumental tolerances from pass-fail and colorimetric data

Equations such as CIE94 and CMC are now in common use to set instrumental tolerances for industrial color control. A visual experiment was performed to generate a data set to be used in evaluating typical industrial practices. Twenty-two observers performed a pass-fail color tolerance experiment for a single high-chroma yellow color. Thirty-two glossy samples varying in all three CIE-LAB dimensions were compared with a single standard. A near-neutral anchor pair was used to define the quality of match criterion. The pooled pass data were used to fit a 95% confidence ellipsoid. The chromaticness dimension was well estimated by either CMC or CIE94. The lightness dimension was poorly estimated by either equation. Evaluating the sampling distribution of the 32 test samples via a covariance matrix revealed a poor sampling, particularly in the ΔL*Δb* plane. This sampling may have biased the visual experiment. The visual data were used to optimize various color-difference equations based on CIE94 and CMC, where the l:c and total color difference were adjustable parameters. Several methods of optimization are described including minimizing the number of instrumental wrong decisions and logistic multiple-linear regression. Some methods require only pass response data, while others require both pass and fail data. Because industrial tolerances are usually based on a single observer, ellipsoids were fitted for three observers to demonstrate the large variability between observers in judging color differences. It was concluded that when tolerances need to be set based on a single observer's visual responses of samples not well distributed about the standard, typical industrial occurences, one should only adjust the tolerance magnitude based on a statistically valid equation such as CIE94. One should not change l:c or derive a new ellipsoid. © 1996 John Wiley & Sons, Inc.     

Color rendering,a reassessment

The deficiencies of the CIE method of measuring and specifying colour rendering properties of light sources are discussed. © 1999 John Wiley & Sons, Inc. Col Res Appl, 24, 197–206, 1999