Calculation of color gamuts based on the Neugebauer model

The calculation of color gamuts is often based on transforming the colorant boundaries to color space. This method works for “well behaved” processes, but in some cases it is necessary to take into account not only these physical boundaries, but also other kinds of boundary surfaces. These additional boundaries are introduced here for 3-ink and 4-ink processes and are called natural and hybrid boundaries. Examples of print processes for which these different kinds of boundaries should be taken into account are given for the Neugebauer and localized Neugebauer model. Finally, an analytical approach is presented for the calculation of color gamuts of “well behaved” processes based on the Neugebauer model. © 1997 John Wiley & Sons, Inc. Col Res Appl, 22, 365–374, 1997     

Formulas for computing correlated color temperature

Formulas by which the correlated color temperature of a light source may be calculated directly from the chromaticity coordinates u and v are introduced. The derivation process of the formulas is described. This method is compared with Robertson's method. It has many advantages.     

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

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

Recursive quadratic programming algorithm for color matching

A recursive quadratic programming (RQP) algorithm for color matching is described. RQP does not work on the assumption that the difference of spectral reflectance between sample and match can be approximated by a first-order expansion. Color matching is instead obtained only by agreement of a trichromatic specification. A numerical example showing a possible field of application of RQP is presented.     

Determining colour gamuts of digital cameras and scanners

The determination of the colour gamuts of colour reproduction media is an important aspect of both understanding them in isolation and using them in the context of a colour reproduction system. Although this is well understood for output colour reproduction media, a solution for input media is not to be had in a simple way. To this end, in this article, we propose a method based on simulating the responses of an input medium to given spectral power distributions. We then determine the gamut of an input medium on the basis of having a set of spectra that covers the majority of all possible spectra, knowing a medium's quantized responses to them, and then determining a boundary beyond which the medium does not produce variation in its responses. © 2002 Wiley Periodicals, Inc. Col Res Appl, 28, 59–68, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.     

Mixed-integer programming algorithm for computer color matching

This article introduces an extension of the linear-programming formulation algorithm already known. A method for the calculation of suboptimal recipes involving a reduced number of colorants is outlined, as well as the possibility of taking into account the effect of incompatibility between pairs of colorants from the complete inventory. Both improvements are based on the introduction of mixed-integer programming techniques, and result in increased usefulness of linear programming for practical applications. A numerical example showing the results obtained with the proposed algorithm is presented.     

基于并行计算的优化方法参数自动整定算法

优化求解器的参数设置对优化求解器的性能有着至关重要的影响,可以通过参数整定来充分发挥优化求解器潜在的求解性能。过程模型复杂程度的提高和规模的增大,给参数自动整定算法的效率带来极大的影响。根据基于随机采样的参数自动整定算法对每一组参数设置的选择和评估是相互独立的特点,采用并行化方法对其进行了改进。数值实验表明基于并行计算的参数自动整定能够提高整定效率,并且在足够的硬件条件支持下适合应用于面向生产过程的操作运行的在线操作优化。     

A spectrophotometric color matching algorithm for precolored fiber blends

In this article, a spectrophotometric color matching algorithm based on Stearns‐Noechel model is proposed. This algorithm was run to predict recipes for 48 viscose blends. Color differences between the original blend samples and the calculated were expressed in CIELAB units (10°standard observer). M (the empirical constant in Stearns‐Noechel model) value was determined by median analysis. When M equals to 0.09, the best fit was obtained for three‐components fiber blends. In that case, the maximum color difference is 1.22 CIELAB units and the average computed color difference is 0.56 CIELAB units for 36 three‐components fiber blends under D65 illuminant. When M is from 0.03 to 0.06, the best fit was obtained for four‐components fiber blends. In that case, the maximum color difference is 4.48 CIELAB units and the average computed color difference is 1.02 CIELAB units for 12 four‐components fiber blends under D65 illuminant. It is demonstrated that the algorithm can be used in color matching of fiber blends. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 108–114, 2009     

Quantification of illuminant metamerism for four coloration systems via metameric mismatch gamuts

Illuminant metamerism was evaluated by generating achromatic metamers for an acrylic-enamel coating, an acrylobutadiene styrene polymer, a polyester textile, and a nylon textile using computer colorant formulation techniques. The tristimulus matching algorithm used to generate the metamers was based on Kubelka-Munk turbid media theory. By definition, each set of metamers that were formulated to match under CIE illuminant D₆₅ for the 1964 CIE standard observer would mismatch under a test illuminant, forming a gamut of colorimetric coordinates. These metameric mismatch gamuts were evaluated quantitatively using multivariate statistics. Illuminants A, F2, and F11, representing incandescent, cool-white fluorescent, and narrow-band fluorescent, respectively, were used as test illuminants. Illuminant similarities, coloration system similarities, tristimulus variability, and reference illuminant selection criteria were evaluated.     

Fast image enhancement based on color space fusion

The current Retinex algorithm processes the RGB channels separately for color image enhancement. However, it changes the ratios of RGB components and also causes some serious problems, such as color distortion, color noise, and the halo artifacts. To solve these issues, we propose a novel algorithm based on color space fusion. The single scale Retinex with fast mean filtering is applied to the luminance component in hue‐saturation‐value (HSV) color space. An enhancement adjustment factor is introduced to avoid color distortion and noise amplification. Then, the surrounding function is replaced by a small scale Gaussian filter in RGB color space to eliminate the halo artifact. A parameter is involved to keep the color natural when the reflection is estimated. Finally, the enhanced color image is constructed from the weighted averaging results of these two steps. The subjective and objective evaluations of many different backlight images captured by different cameras are implemented to verify the validity of the proposed algorithm in our experiments. The experimental results show that the proposed algorithm can not only significantly suppress the halo effect and noise amplification, but can also remove color distortion. Our proposed algorithm is superior to the multi‐scale Retinex with color restoration approach and other state‐of‐the‐art methods. © 2014 Wiley Periodicals, Inc. Col Res Appl, 41, 22–31, 2016     

An algorithm for computing the asymptotic fisher information matrix for seasonal SISO models

Abstract.  The paper presents an algorithm for computing the asymptotic Fisher information matrix of a possibly seasonal single-input single-output (SISO) time-series model. That matrix is a block matrix whose elements are basically integrals of rational functions over the oriented unit circle. The procedure makes use of the autocovariance or the cross-covariance function of two autoregressive processes based on the same noise. The algorithm also works when the input variable is omitted, the case of a seasonal ARMA model.     

Comparison of real colour gamuts using a new reflectance database

A large set of data, comprising the spectral reflectances of real surface colours, has been accumulated. The data comprise 16 groups with different materials and include 85,879 measured spectra. From these data, CIELAB colorimetric coordinates were calculated under CIE illuminant D50 and the CIE 1931 standard colorimetric (2°) observer. Several published colour gamuts including those developed by Pointer and ISO reference colour gamut [ISO Graphic Technology Standard 12640‐3:2007] were compared using the present data set. It was found that the Pointer gamut is smaller than the new real data in most of the colour regions. The results also showed that the ISO reference colour gamut is larger than the new real accumulated data in most regions. The present finding indicates that there is a need to derive a new colour gamut based on the newly accumulated data for common applications. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 442–451, 2014     

An algorithm for generating color scales for both categorical and ordinal coding

Previous research has shown multihue scales to be well‐suited to code categorical features and shown lightness scales to be well‐suited to code ordinal quantities. We introduce an algorithm, Motley, that produces color scales varying in both hue and lightness, intended to be effective for both categorical and ordinal coding, allowing users to determine both absolute and relative quantities efficiently and accurately. The algorithm first determines the lightnesses of scale colors to maximize perceived lightness differences and establish the lightness ordering, generating separate search spaces for each scale position. It then selects hues by heuristic search to maximize the discriminability of the scale. It produces scales that are ordered with respect to lightness but unordered with respect to hue and thus more discriminable than typical multihue lightness scales. In an experimental evaluation on human subjects, Motley's scales enabled accurate judgments of relative quantity, with response times superior to unordered multihue scales and comparable to ordered lightness scales, and enabled accuracy and speed of judgments of absolute quantity superior to lightness scales and comparable to multihue scales. Published 2009 Wiley Periodicals, Inc., Col Res Appl, 2010.     

Reflective color reduction using genetic algorithm optimization

A subset of colors often needs to be selected to represent a full set. In one such application, a multi‐band color sensor is used to measure reflective color samples, and a matrix transformation method is used to recover the reflectance spectrum of the measured sample. To achieve this, a group of training colors needs to be selected to calculate the transformation matrix. A genetic algorithm (GA) has been developed to optimize the selection of the subset of training colors, and the result is compared with those obtained using random selection or a traditional culling algorithm. In a simulation study, the GA gives better results.     

An algorithm for the selection of high‐contrast color sets

Nominal color coding is the aesthetic and functional use of color to convey qualitative information in graphical environments. The specification of high‐contrast color sets is a fundamental step in this process. We formulate the color‐coding problem here as a combinatorial optimization problem on graphs and present an algorithm that performs well and does not require that the function used to code the similarity between colors be a distance function. © 1999 John Wiley & Sons, Inc. Col Res Appl, 24, 132–138, 1999     

A new algorithm for computing distance matrix and Wiener index of zig-zag polyhex nanotubes

The Wiener index of a graph G is defined as the sum of all distances between distinct vertices of G. In this paper an algorithm for constructing distance matrix of a zig-zag polyhex nanotube is introduced. As a consequence, the Wiener index of this nanotube is computed.     

一种基于并行计算的混合算法优化有分流换热网络

换热网络优化是化工过程系统工程领域的研究难点,其数学模型具有高度的非凸、非线性,在使用单一启发式算法优化时,往往具有局限性。研究以换热网络的年综合费用最小为目标,针对强制进化随机游走（RWCE）算法在优化时由于个体间独立进化,导致优化过程中信息缺乏交流的问题,提出将遗传算法（GA）与其混合。混合后的算法在保持前一半优势种群中的个体单独进化的基础上,通过周期性的交叉、变异等操作产生子代来替换掉劣势种群,从而增强了原有算法的整型变量优化能力,并弥补了弱势个体无法更新的不足。为了兼顾算法在大种群下优化有分流换热网络的计算效率,节约时间成本,使用OpenMP系统将混合算法实现了并行化设计。通过三个不同规模的换热网络问题对并行后的混合算法进行验证,结果表明该算法能在有效提升优化质量的前提下相比串行算法大幅缩短计算时间,其中两个算例突破了目前文献最优解。     

Colour gamuts arising from absorber–dielectric–metal optical resonators

Structural coloration is a quickly growing field, encompassing physical and photonic processes such as interference, diffraction, and scattering. In this study, we investigated the optical effects in the visible wavelength range, and in particular, the colour gamuts achievable with absorber–dielectric–metal sandwich structures. These chemical‐free layered structures are highly tunable, easily scaled, optical cavities that are capable of generating remarkable colours whose properties are determined completely by material and structural parameters. We employed experimental and numerical strategies to demonstrate that each absorber spans a unique colour gamut, i.e. a subset of the full chromaticity space. While gamut overlap is observed between different absorber types, the gamut areas unique to each absorber occur at different hues of high excitation purity. A comprehensive understanding of how these colour gamuts develop and how different materials may be combined to expand larger subsets of the chromaticity space is required in order to maximize the variety of colours achievable with this system and elevate it into a ‘structural coloration technology’.