CIE Tristimulus Values Research Articles

A biconcave-shaped random laser array for unclonable coding

Photonic barcodes with random fingerprints possess significant potential applications in anti-counterfeiting and security protection due to their unclonable characteristics. Here, a scalable coding strategy is proposed to realize the physical unclonable function (PUF) codes based on a random-distributed biconcave-cavity random laser (BCRL) array in microchannel. Its unique configuration exhibits scalable randomness induced by microcavities and the scatterers, demonstrating a PUF characteristics in lasing intensity variations with pump positions. The random intensity information is firstly used as 1st-order coding to generate the PUF codes. The CIE tristimulus values of the tricolor lasing is then established as 2nd-order coding. The obtained codes strongly rely on the relative position of the arrays, indicating excellent unclonability and high generation efficiency. This work supplies a low-cost way to generate PUF codes for security system, promoting random lasing applications in security protection.

Evaluation of Color Properties of Wool Fabrics Dyed with Calligonum comosum at Different Dye Conditions

In this search, the wool fabric was dyed with a natural dye Calligonum comosum (Callig. Co. dye); the dyeing process was applied under different conditions by changing dye bath temperature, time of dyeing, and pH of dye bath also using different mordants. Ultraviolet protection factor (UPF) was determined for each dyed wool sample. The role of these dying conditions on the via color strength analysis their effects on the reflectance spectra were investigated using the spectro-photometer tool, CIE tristimulus values, and the color parameters. The dye-ability strength and fastness to washing and perspiration properties of these wool samples dyed with (Callig. Co. dye) were carried out spectrophotometrically and evaluated the antimicrobial activity for blank and dyed wool fabrics via gram-positive and gram-negative was followed. The results showed that dyeing wool fabrics with (Callig. Co. dye) increased their protective abilities markedly, and they have effective protection against UV rays, also improving their antimicrobial activity. Moreover, Different conditions of the dye bath changed the optical properties noticeably. The present study will be useful for dermatologists advising patients regarding the UPF properties of clothes made from natural fabrics (wool) and dyed with natural colorants (Callig. Co. dye).

Effect of TiO2 nanoparticles on the structural configurations and thermal, mechanical, and optical properties of chitosan/TiO2 nanoparticle composites

The solution casting method was used to prepare nanocomposite films of chitosan/TiO2 nanoparticles (NPs) because of their applications in various fields. The effects of TiO2NP concentration on the structural, morphological, thermal, mechanical, and optical properties of such films were studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, and thermal analysis (thermogravimetric analysis [TGA] and differential scanning calorimetry [DSC]). The XRD patterns reveal miscibility between the amorphous components of chitosan and TiO2NPs. The HRTEM and FESEM images illustrate the distribution and dispersion of TiO2NPs on the film surface. Data from FTIR spectroscopy, DSC, and TGA and the mechanical properties indicate the dependence of chitosan properties on the presence of TiO2NPs and the existence of interactions between chitosan and TiO2NPs. The reflectance and transmittance values obtained were used to calculate the CIE tristimulus values, color parameters, refractive index, absorption coefficient, dielectric spectra, optical conductivity, volume energy loss function (VELF), and surface energy loss function (SELF). The dependence of the absorption coefficient on the photon energy demonstrated that the optical transfer is permissible and direct. The variations of the dielectric spectra and optical conductivity indicate different interactions between photons and electrons in the films produced and relate to the electronic structure. The values of the VELF were found to be greater than those of the SELF, which confirms that the energy loss occurred mostly within the material. Films were also examined for water vapor transmission (WVT) and water vapor permeability (WVP), and the results showed that incorporation of TiO2NPs onto chitosan caused a decrease of WVT and WVP. In addition, the antimicrobial activity of the nanocomposite films against Gram-positive and Gram-negative bacteria was studied, and good antimicrobial activity was found, indicating their ability to inhibit bacterial proliferation at the culture site. The developed chitosan thin films supporting an optimized amount of TiO2NPs could be used to treat various diseases.

Methods for improving the accuracy of CIE tristimulus values of object color by calculation Part II: Improvement on measurement wavelength ranges

The previous paper (part I) analyzed test errors of the spectrophotometer and their reasons, then systematically investigated the algorithms to reduce measuring bandpass error and intervals error. This paper (part II) focuses on the influence of measurement wavelength ranges and their truncation errors, and some algorithms to overcome the truncation errors. CIE recommends that tristimulus values are calculated over a range of 360–830 nm. However, most spectrophotometers do not meet it. The reduction of measurement range will result in a measurement range error or a truncation error. In this study, five ranges commonly employed in practice are selected for investigating the truncation errors, and three extrapolation methods are used to extend the data to compensate for the measurement range loss. Results are obtained by employing 1301 Munsell color chips under illuminant D65 and CIE 1964 standard observer. For the standard 1-nm intervals, the narrower the range, the larger the truncation error. For the usual-measured 10-nm intervals, bandpass error and intervals error should be handled at the same time, 380–780 nm Table LWL gives the highest accurate outcomes, which even improve the accuracy of the range 360–750 nm to an acceptable level. Whereas, ranges of 360–700 nm and 400–700 nm still need extrapolation to reduce their truncation errors even with Table LWL. Three extrapolation methods of nearest, linear and second-order all reduce the truncation error, but for different ranges, algorithms and illuminants, the optimal method of extrapolation varies.

Macrostructure and optical studies of hydroxypropyl cellulose in pure and Nano-composites forms

In the present study, composites of hydroxypropyl cellulose and iron (III) oxide nanoparticles (HPC:Fe2O3 NPs) were prepared in different ratios (20:0.5, 20:1, 20:1.5 and 20:2 wt:wt). Variations in the group coordination of the prepared composites in the IR region were employed. The reflectance spectra in the visible region (400–700 nm) were followed to characterize and reveal the relationship of the structure properties of the prepared nanocomposites. The CIE tristimulus values and color parameters as well as the location on the chromaticity diagram were determined. The variations in the optical parameters such as; absorption coefficient, absorption edge, band tail width and band gap energies, extinction coefficient and color strength were determined as a function of α-Fe2O3 NPs concentrations. The results of the FTIR spectra noticed that by increasing the concentration of Fe2O3 NPs in the mixture, variations in the intensity, area, band width, and the transmittance values of some bands were observed which indicate that change in the vibrational bonds and in the molecular configuration of HPC was occurred. The location of the α-Fe2O3 NPs concentration on the chromaticity diagram was different and confirmed the change in the colors of the investigated composites. The obtained variations in the optical parameters by increasing the presence of α-Fe2O3 NPs may be due the induced structural change in the system of HPC. In conclusion, increasing the existence of α-Fe2O3 NPs in the HPC network has great effect on improving the performance properties of hydroxypropyl cellulose.

Color prediction of metallic coatings from measurements at common geometries in portable multiangle spectrophotometers

Illuminating and viewing geometries may strongly affect the color appearance of metallic coatings, which can be characterized accurately by bidirectional reflectance distribution function (BRDF) measurement devices. However, such devices with hundreds or even thousands of different geometries are usually expensive and complex. Accordingly, two modified models were developed in this study, based on the distribution of aluminum-flake pigments in the coatings, to, respectively, estimate the spectral radiance factors and the CIE tristimulus values of metallic coatings utilizing the measurements at 6 common geometries of portable multiangle spectrophotometers. Their performance was examined with 65 achromatic and 20 chromatic metallic coating samples under D65, A, and F11 illuminants. The average CIEDE2000 color differences over all 19 geometries were found to be less than 1.8 for both models, while the average CAM02-SCD and CIELAB color differences can, respectively, reach 1.7 and 2.0, indicating the effectiveness of our methods.

Effect of classification by competitive neural network on reconstruction of reflectance spectra using principal component analysis

AbstractThe best way to describe a color is to study its reflectance spectrum, which provide the most useful information. Different methods were purposed for reflectance spectra reconstruction from CIE tristimulus values such as principal components analysis. In this study, the training samples were first divided into 3, 6, 9, and 12 subgroups by creating a competitive neural network. To do that, L*a*b*, L*C*h or L*a*b*C*h were introduced to neural network as input elements. In order to investigate the performance of reflectance spectra reconstruction, the color difference and RMS between actual and reconstructed data were obtained. The reconstruction of reflectance spectra were improved by using a six or nine‐neuron layer with L*a*b* input elements. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 182–188, 2017

Interpolation, extrapolation, and truncation in computations of CIE tristimulus values

AbstractThis article addresses some general practices for the computation of CIE tristimulus values (TSVs), including different methods used for the interpolation, extrapolation, and truncation of data in the visible wavelength range. In each case, a quantitative analysis is presented on the basis of a dataset with 2365 spectral reflectances covering a wide color gamut, assuming six CIE illuminants and the two CIE standard colorimetric observers. For interpolation, it is found that among five tested methods, the (cubic) spline method is the best one when the spectral reflectance factors are uniformly sampled over the visible wavelength range. For extrapolation, it is found that the second‐order extrapolation method gives better results than the use of nearest available data points or linear extrapolation methods. With respect to truncation, considering five different usual truncated ranges, it is found that the range from 360 to 780 nm provides more accurate results than the range from 380 to 780 nm currently recommended by CIE for nonfluorescent samples, and the use of the truncated range from 400 to 700 nm in place of the CIE‐recommended range of 360 to 830 nm leads to TSVs with considerably high color differences of up to 0.9 CIELAB units. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 10–18, 2017

Reflectance spectra recovery from tristimulus values by extraction of color feature match

A procedure for recovering spectral reflectance from CIE tristimulus values is presented using a modified pseudo-inverse method. Unlike previous spectral recovery methods, this approach uses a new sample selection criterion based on color feature match to select a series of suitable samples for creating the adapted transformation matrix to reconstruct spectra reflectance. Taking into account the computational time and accuracy, the dynamic subgroups were created by dividing the spectral reflectance preliminarily, and the adapted subsets were created by the sample similarity/dissimilarity between samples in the dynamic subgroup and target sample. Consequently, instead of applying only one transformation matrix for the reconstruction process, a series of adapted transformation matrices were obtained from the adapted subsets using color feature match. Three different datasets of spectral reflectance and three different error metrics have been applied in this study. According to all the error metrics considered, the proposed method is quite accurate and outperforms the Pseudo-Inverse method and the weighted Pseudo-Inverse method, which is effective in reconstructing spectral reflectance.

Spectral Color Reproduction from CIE Tristimulus Values Using a Node Address Array Selection Technique

This study proposes a feasible method for spectral color reproduction based on a node address array selection technique from CIE tristimulus values. In this method three-dimensional lookup table (3-D LUT) has been constructed to connect the node address array and the spectrum as the source and destination spaces. First we present a general framework for how to reproduce spectral color. Then results of recovery are evaluated by the root mean square error (RMSE) and the color difference CIE ∆E00. According to the results considered, the proposed method could reconstruct the spectral reflectance with a high spectral and colorimetric accuracy.

Prediction of emission spectra of fluorescence materials using principal component analysis

AbstractFluorescent materials are now a critical field of research due to their unique excitation and emission properties that can be tailored to specific fluorescence detection technologies. In this work, a procedure is described to approximate the emission spectral data of fluorescent materials of different types from their excitation spectral data using principal component analysis (PCA) technique. First, PCA as a statistical and mathematical method was used to reconstruct the excitation and emission spectra of training dataset and then, the approximation was accomplished by multiple linear regression (MLR).The performance of obtained function was examined on testing dataset. Afterward, CIE tristimulus values of the fluorescent samples were calculated based on ASTM, E2152–12 standard test method. The colorimetric accuracy was then evaluated by calculating the geometric differences in CIE tristimulus values X, Y, and Z for the 1964 standard colorimetric observer under illuminant D65. The obtained results show a good curve fit between the actual emission spectra and recovered emission spectra. In addition, based on cumulative variance and root mean square (RMS), eight principal components were selected as optimum number of principal components for prediction of emission spectra data. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 16–21, 2016

Effect of temperature on the evolution of colour during the maceration of fruits in liquor

The effect of temperature on the kinetics of pigment extraction during the maceration of different fruits (raspberry, blackberry, and cranberry) into a commercially available hard spirit (orujo, with 42% v/v ethanol) was evaluated. The analytical method used was UV-Vis spectrophotometry. The initial extraction rate showed an Arrhenius-type dependence with apparent energy activation of 28.8, 69.8, and 55.6 kJ/mol, respectively. Furthermore, a study about the evolution of the colour (from colourless to reddish colour appearance) during the soaking process was done by calculating the CIE tristimulus values (X, Y, Z) for illuminant C, until reaching the apparent stabilisation of colour, which occurs after about two to four weeks for the studied temperatures (5, 23, and 40°C). Studies about the evolution of colour in the soaking process of this kind of fruit liquors can lead to a better understanding of this process, and thus to a better control over the mechanisms underlying it.  

Comparison of the performance of inverse transformation methods from OSA-UCS to CIEXYZ

The Optical Society of America's Uniform Color Scales (OSA-UCS) is one of the color spaces that most closely approximate a "true" uniform color space. Different techniques have been used to convert OSA-UCS-based color specification parameters, L, j, and g, to the CIE tristimulus values, X, Y, and Z. However, none of these methods provides a direct method of inverting OSA-UCS to CIEXYZ values. Thus, numerical algorithms, such as the Newton-Raphson method, have been employed to obtain the transformations. The relative low accuracy and long computation time of this method makes it undesirable for practical applications. An artificial neural network (ANN) was employed to convert OSA-UCS to CIEXYZ. Its performance was compared with that of numerical methods. After optimization, ANN gave a better performance with a mean error (ΔEXYZ) of 1.0×10(-4) and a conversion time of less than 1 s for 1891 samples.

Crosstalk characterization method for stereoscopic three-dimensional television

A crosstalk characterization model is proposed that shows the relationship between colors with and without crosstalk by using CIE tristimulus values. The proposed model is based on the 3D color measurement results of two different stereoscopic 3D televisions with shutter glasses, namely, a PDP and an LCD. The PDP exhibits a significant dependence of crosstalk on channel and tristimulus values, meaning that different channels and wavelengths result in different degrees of crosstalk, while the LCD exhibits little channel or wavelength dependence. Moreover, for PDP, the proportion of leaked light increases as the luminance of the opposite view decreases. In spite of different crosstalk characteristics, both PDP and LCD show similar performance resulting in 1.5ΔE* <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ab</sub> and 1.9ΔE* <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ab</sub> average color difference between the measured and the predicted. The proposed model could be used to develop a better crosstalk metric or a crosstalk cancellation algorithm by more accurately predicting colors including crosstalk.

Visual gamma correction for LCD displays

An improved method for visual gamma correction is developed for LCD displays to increase the accuracy of digital colour reproduction. Rather than utilising a photometric measurement device, we use observers’ visual luminance judgements for gamma correction. Eight half tone patterns were designed to generate relative luminances from 1/9 to 8/9 for each colour channel. A psychophysical experiment was conducted on an LCD display to find the digital signals corresponding to each relative luminance by visually matching the half-tone background to a uniform colour patch. Both inter- and intra-observer variability for the eight luminance matches in each channel were assessed and the luminance matches proved to be consistent across observers (Δ E 00 < 3.5) and repeatable (Δ E 00 < 2.2). Based on the individual observer judgements, the display opto-electronic transfer function (OETF) was estimated by using either a 3rd order polynomial regression or linear interpolation for each colour channel. The performance of the proposed method is evaluated by predicting the CIE tristimulus values of a set of coloured patches (using the observer-based OETFs) and comparing them to the expected CIE tristimulus values (using the OETF obtained from spectro-radiometric luminance measurements). The resulting colour differences range from 2 to 4.6 Δ E 00. We conclude that this observer-based method of visual gamma correction is useful to estimate the OETF for LCD displays. Its major advantage is that no particular functional relationship between digital inputs and luminance outputs has to be assumed.

Estimation of CIE tristimulus values under various illuminants

AbstractIn this work, a procedure is described to estimate the CIE tristimulus values of Munsell color chips under new illuminants from CIE tristimulus values under specific illuminant. The estimation was performed by multiple linear regression (MLR) and principal component analysis (PCA) techniques. In addition, the effects of illuminants combination and Munsell hue, value and chroma on reconstruction of CIE tristimulus values were evaluated in both methods. The results obtained indicate that the performance of principal component method is better than multiple regression method. The accuracy of estimation depends on the initial and target illuminants and hue, chroma and value of samples. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 100–107, 2009

Colour calibration of a laboratory computer vision system for quality evaluation of pre-sliced hams

Due to the high variability and complex colour distribution in meats and meat products, the colour signal calibration of any computer vision system used for colour quality evaluations, represents an essential condition for objective and consistent analyses. This paper compares two methods for CIE colour characterization using a computer vision system (CVS) based on digital photography; namely the polynomial transform procedure and the transform proposed by the sRGB standard. Also, it presents a procedure for evaluating the colour appearance and presence of pores and fat-connective tissue on pre-sliced hams made from pork, turkey and chicken. Our results showed high precision, in colour matching, for device characterization when the polynomial transform was used to match the CIE tristimulus values in comparison with the sRGB standard approach as indicated by their Δ E ab ∗ values. The [3 × 20] polynomial transfer matrix yielded a modelling accuracy averaging below 2.2 Δ E ab ∗ units. Using the sRGB transform, high variability was appreciated among the computed Δ E ab ∗ (8.8 ± 4.2). The calibrated laboratory CVS, implemented with a low-cost digital camera, exhibited reproducible colour signals in a wide range of colours capable of pinpointing regions-of-interest and allowed the extraction of quantitative information from the overall ham slice surface with high accuracy. The extracted colour and morphological features showed potential for characterizing the appearance of ham slice surfaces. CVS is a tool that can objectively specify colour and appearance properties of non-uniformly coloured commercial ham slices.

Representing Colors as Three Numbers

RGB in graphics is both a way of specifying color and a way of viewing color. Graphics algorithms manipulate RGB colors, and the images produced by graphics algorithms are encoded as RGB pixels and displayed on devices that render these pixels by emitting RGB light. Colored images are also used to specify color in graphics. Most computer graphics texts and tutorials provide a description of human color vision and measurement as defined by the CIE tristimulus values, XYZ. Often missing, however, is an in-depth discussion of the relationship between the different applications of RGB and XYZ, and any discussion of color models beyond trichromacy. The goal of this tutorial is to provide a complete, concise analysis of RGB color specification and its relationship to perceptual and physical specifications of color, and to introduce some models for color perception beyond tristimulus theory.

White gold alloys:

A numerical grading system has been established for white gold alloys using the ASTM Yellowness Index D1925, an existing colour quality standard. The Index is calculated from the CIE (International Commission of Illumination) Tri-stimulus values, X, Y and Z, and the scale is linear, so that as the number decreases, the alloy becomes whiter. This Index provides values that have good correlation with visual assessments and permits easy differentiation of colour without knowledge of an alloys composition. The use of a spectrophotometer instrument provided a quick means of sample colour measurement, with high precision and accuracy.

Metameric matching and its compensation with individual color matching functions

Match in tristimulus values using CIE standard observer is the most popular way to make two colors of different spectral power distributions look identical. This metameric match, however, does not always guarantee those two colors appears the same for individual observer. This may be because the CIE color matching functions (CMFs) are different from those of individual observer. In FVM2003, we showed some individual differences in CMFs. Here, we conducted metameric matching experiments to see whether mismatch in CIE tristimulus values can be explained by compensating individual CMFs. The experiments were conducted on three subjects whose CMFs were measured with our methods. A subject, whose head position was fixed with a chin rest, was asked to make match between a reference and a test stimulus by observing them alternatively and by adjusting color of the test stimulus. Color paper and a CRT monitor were used to present the reference and the test stimulus, respectively. The surrounding of the stimuli was dark. Each subjects conducted 5 to 10 sessions for 7 test colors. The CIE tristimulus values of the test and the reference were different for colors of metameric pairs, and the data showed individual differences. In order to obtain the customized tristimulus values, we applied the individual CMFs to the spectrum of the test and the reference stimuli. Such compensation showed some improvement for several metameric pairs, but not for all pairs. Our results indicate that it is effective to take individual CMFs into consideration for the metameric matching. A part of the results was obtained through the activities of the research group “Evaluating individual color matching functions.”