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1.
In this article, we are combining minimization criteria in the colorant separation process for spectral color reproduction. The colorant separation is performed by inverting a spectral printer model: the spectral Yule‐Nielsen modified Neugebauer model. The inversion of the spectral printer model is an optimization operation in which a criterion is minimized at each iteration. The approach we proposed minimizes a criterion defined by the weighted sum of a spectral difference and a perceptual color difference. The weights can be tuned with a parameter α ∞ [0, 1]. Our goal is to decrease the spectral difference between the original data and its reproduction and also to consider perceptual color difference under different illuminant conditions. In order to find the best α value, we initially compare a pure colorimetric criterion and a pure spectral criterion for the reproduction, then we combine them. We perform four colorant separations: the first separation will minimize the 1976 CIELAB color difference where four illuminants are tested, the second separation will minimize an equally weighted summation of 1976 CIELAB color difference with the four illuminants tested independently, the third colorant separation will minimize a spectral difference, and the fourth colorant separation will combine a weighted sum of a spectral difference and one of the two first colorimetric differences previously introduced. This last colorant separation can be tuned with a parameter in order to emphasize on spectral or colorimetric difference. We use a six colorants printer with artificial inks for our experiments. The prints are simulated by the spectral Yule‐Nielsen modified Neugebauer model. Two groups of data are used for our experiments. The first group describes the data printed by our printing system, which is represented by a regular grid in colorant space of the printer and the second group describes the data which is not originally produced by our printing system but mapped to the spectral printer gamut. The Esser test chart and the Macbeth Color Checker test chart have been selected for the second group. Spectral gamut mapping of this data is carried out before performing colorant separation. Our results show improvement for the colorant separations combining a sum of 1976 CIELAB color difference for a set of illuminants and for the colorant separation combining a sum of 1976 CIELAB color difference and spectral difference, especially in the case of spectral data originally produced by the printer. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 494–504, 2008 相似文献
2.
Hung‐Shing Chen Shih‐Han Chen Yen‐Hsiang Chao M. Ronnier Luo Pei‐Li Sun 《Color research and application》2014,39(2):154-168
In the highly competitive display market, manufacturers continuously develop new technologies to improve the image quality of displays. However, color measurement and visual assessment are time‐consuming to production lines. A new method to measure and improve color quality of the displays automatically therefore, is urgently needed to the manufacturers. This article proposes a familiar color correction strategy to optimize the colors of different displays by means of creating an image‐based color palette which enables color correction for familiar objects (e.g., facial skin, blue sky, or green grass) in the multidisplay systems. To produce the image‐based color palette, the 8‐bit RGB value of each pixel in an image is transformed to L*d*n* (lightness/dominant color/nondominant color) color channels, and the dominant‐color regions in an image are subsequently extracted from the dominant color (d*) channel. The memory color data of familiar objects can be set in reference monitor in advance to determine the dominant color (d*) channel. Then a series of palette colors are generated around a displayed image. The color palette will be displayed as a target for two‐dimensional colorimeter shooting to obtain the measured color data. The familiar color correction model was established based on a first‐order polynomial regression to achieve a polynomial fit between the measured color data and the reference color data on the color palette. The proposed method provides a solution to correct familiar colors on a displayed image, and maintains the original color gamut and tone characteristic in the multidisplay systems simultaneously. It is possible to achieve the preferred intent of the displayed images by using the proposed familiar color correction method. © 2012 Wiley Periodicals, Inc. Col Res Appl, 39, 154–168, 2014 相似文献
3.
Hung‐Shing Chen Te‐Mei Wang Shih‐Han Chen Jin‐Sin Liu 《Color research and application》2011,36(5):335-348
The development of wide color gamut (WCG) liquid crystal display (LCD) plays an important role in the high‐quality television (TV) field. Nowadays, people want their TV or display devices to have the capability of showing vivid colors while keeping skin colors as natural as they remember. Therefore, it is necessary to develop color‐correction technologies for WCG LCD system. A new color‐correction method named “natural skin‐color mapping algorithm” (NSCMA) for WCG LCD is proposed in this study. It can solve the skin‐color contour problem in color‐corrected images with simple skin‐color detection. Its development is based on the concepts of performing color mapping between source hue colors and target hue colors on each hue page. The polynomial regression is also applied to calculate the color mapping conversion matrices. Two color mapping factors called template‐size factor and tone‐compression factor are designed in NSCMA. The template‐size factor is used to adjust target template sizes adequately. The tone‐compression factor is designed to control the degrees of image enhancement. For facial skin‐color pictures, the appropriate settings of template‐size factor and tone‐compression factor will get suitable color image rendering on the WCG LCD. It is demonstrated that the WCG LCD can be corrected to show vivid color pictures and keep facial skin colors as natural as possible when the proposed NSCMA is performed. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2011 相似文献
4.
Michael J. Murdoch Dragan Sekulovski Ingrid Heynderickx 《Color research and application》2014,39(2):169-178
Preferred chroma enhancement and its dependence on hue are studied in a two‐part experiment using a wide‐gamut multiprimary display. Earlier research showed a clear dependence on hue but was limited by the gamut of the display it employed; the present work builds on this while easing the gamut constraints. In the first part of the present experiment, a tuning task was used to refine the preference for chroma boost starting with standard‐gamut (Rec. 709) images. The overall median preferred boost is roughly 20%, but it is not uniform over hues: the preferred boost for orange, yellow, green, and cyan colors is greater than that for blue, magenta, and red colors. Dependence on image content and observer is noted, though a content‐independent chroma boost created by aggregating preference over many images performs well. An adjustment parameter for overall chroma, which incorporates the hue dependence averaged over image content, should be sufficient to handle the vast majority of interobserver variance in preference. In the second part of the experiment, various chroma boost algorithms were evaluated through a paired comparison task. The prescribed hue‐dependent chroma boost is preferred over all other variations, and all hue‐preserving chroma boost variations are preferred over both colorimetrically accurate and na??ve same‐drive‐signal renderings. The results may be applied in display design to select gamut boundaries that maximize satisfaction over the observer population. © 2012 Wiley Periodicals, Inc. Col Res Appl, 39, 169–178, 2014 相似文献
5.
In this article, we proposed a new method based on natural neighbor interpolation to recover the spectral reflectance of objects from an image captured by a traditional Red‐Green‐Blue (RGB) digital camera. The concept of model‐based metameric spectra of eight extreme points in the standard RGB (sRGB) color gamut was further introduced to ensure that almost all test samples in the entire gamut can be simply and properly recovered without needing the extrapolation or any other auxiliary techniques. The quasi‐Newton method was used to estimate iteratively the optimal parameters of these metameric spectra, satisfying the constraints of the gamut extreme points. Several experiments were performed. The effectiveness of the method with and without the metameric spectra was evaluated, including some performance comparisons with the principal component analysis (PCA) method of transformational type (classic PCA and weighted PCA) and that of interpolation type. The results showed that the proposed method greatly enlarged the accurately applicable domain of the interpolation strategy and offered spectra with feasibility and naturalness much superior to the PCA‐based methods. The proposed method was obviously better than the conventional interpolation ones, and had a similar performance with the weighted PCA method in terms of color difference. 相似文献
6.
为了研究不同类型输出设备对数字输出阶调再现特性的影响,选用彩色喷墨打印机Epson R250、Epson 1390、Epson 7908和Canon iPF6350,彩色激光打印机Epson C8600和Hp 4700N,热升华打印机Canon730和Sony FP97等三类输出设备对数字输出阶调再现性能进行测试和比较,得出结论:彩色喷墨打印机在图像的亮调部分再现阶调能力优于彩色激光打印机,彩色激光打印机在图像的暗调部分再现阶调能力优于彩色喷墨打印机,热升华打印机的阶调层次再现能力较好且色域相对较大。 相似文献
7.
为了了解不同纸张对数字输出阶调特性的影响,采用CorelDraw软件制作单色色阶测试版,选择常用的普通打印纸、一般照片纸和光泽照片纸在Epson Stylus Photo R250彩色喷墨打印机上进行输出,用DS分光光度仪对输出色阶进行CIEL*a*b*色度值的测量,用色彩管理软件为不同纸张制作特性文件,对不同纸张所能达到的数字输出阶调特性进行定量分析。针对选用的纸张进行测量后得出结论,输出色彩丰富的图像优选的纸张应是光泽照片纸,输出灰度层次丰富的图像可以选择普通打印纸。 相似文献
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The recommendation of the CIE has been followed as closely as possible to evaluate the accuracy of five color gamut mapping algorithms (GMAs)—two nonspatial and three spatial algorithms—by psychophysical experiments with 20 test images, 20 observers, one test done on paper and a second one on display. Even though the results do not show any overall “winner,” one GMA is definitely perceived as not accurate. The importance of a high number of test images to obtain robust evaluation is underlined by the high variability of the results depending on the test images. Significant correlations between the percentage of out‐of‐gamut pixels, the number of distinguishable pairs of GMAs, and the perceived difficulty to distinguish them have been found. The type of observers is also important. The experts, who prefer a spatial GMA, show a stronger consensus and look especially for a good rendering of details, whereas the nonexperts hardly make a difference between the GMAs. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 470–476, 2008 相似文献
10.
In recent years, new display technologies have emerged that are capable of producing colors that exceed the color gamut of broadcast standards. On the other hand, most video content currently remains compliant with the EBU standard and as such, there is a need for color mapping algorithms that make optimal use of the wider gamut of these new displays. To identify appropriate color mapping strategies, we have developed, implemented, and evaluated several approaches to gamut extension. The color rendering performance and robustness to different image content of these algorithms were evaluated against a reference (true‐color) mapping. To this end, two psychophysical experiments were conducted using a simulated and actual wide‐gamut display. Results show that the preferred algorithm had a dependency on image content, especially for images with skin tones. In both experiments, however, there was preference shown for the algorithm that balances chroma and lightness modulations as a function of the input lightness. The newly designed extension algorithms consistently outperformed true‐color mapping, thus confirming the benefit of appropriate mapping on wide‐gamut displays. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 443–451, 2009 相似文献
11.
Dorukalp Durmus 《Color research and application》2020,45(5):796-802
A color space is a three-dimensional representation of all the possible color percepts. The CIE 1976 L*a*b* is one of the most widely used object color spaces. In CIELAB, lightness L* is limited between 0 and 100, while a* and b* coordinates have no fixed boundaries. The outer boundaries of CIELAB have been previously calculated using theoretical object spectral reflectance functions and the CIE 1931 and 1964 observers under the CIE standard illuminants D50 and D65. However, natural and manufactured objects reflect light smoothly as opposed to theoretical spectral reflectance functions. Here, data generated from a linear optimization method are analyzed to re-evaluate the outer boundaries of the CIELAB. The color appearance of 99 test color samples under theoretical test spectra has been calculated in the CIELAB using CIE 1931 standard observer. The lightness L* boundary ranged between 6 and 97, redness-greenness a* boundary ranged between −199 and 270, and yellowness-blueness b* boundary ranged between −74 and 161. The boundary in the direction of positive b* (yellowness) was close to the previous findings. While the positive a* (redness) boundary exceeded previously known limits, the negative a* (greenness) and b* (blueness) boundaries were lower than the previously calculated CIELAB boundaries. The boundaries found here are dependent on the color samples used here and the spectral shape of the test light sources. Irregular spectral shapes and more saturated color samples can result in extended boundaries at the expense of computational time and power. 相似文献
12.
Anustup Choudhury Robert Wanat Jaclyn Pytlarz Scott Daly 《Color research and application》2021,46(1):46-64
High dynamic range (HDR) and wide color gamut imagery has an established video ecosystem, spanning image capture to encoding and display. This drives the need for evaluating how image quality is affected by the multitudes of ecosystem parameters. The simplest quality metrics evaluate color differences on a pixel‐by‐pixel basis. In this article, we evaluate a series of these color difference metrics on four HDR and three standard dynamic range publicly available distortion databases consisting of natural images and subjective scores. We compare the performance of the well‐established CIE L*a*b* metrics (ΔE00 , ΔE94 ) alongside two HDR‐specific metrics (ΔEZ [Jzazbz], ΔEITP [ICTCP]) and a spatial CIE L*a*b* extension (). We also present a novel spatial extension to ΔEITP derived by optimizing the opponent color contrast sensitivity functions. We observe that this advanced metric, , outperforms the other color difference metrics, and we quantify the improved performance with the steps of metric advancement. 相似文献
13.
The aim of this article is to present the evaluation of gamut mapping algorithms (GMAs) in a series of three experiments intended to serve as the basis for developing solutions that are accurate and universally applicable. An evolutionary gamut mapping development strategy is used, in which five test images are reproduced between a CRT and printed media obtained using different GMAs. Initially, a number of previously published algorithms were chosen and psychophysically evaluated, whereby an important characteristic of this evaluation was the separate evaluation for individual colour regions within test images. New algorithms were then developed on this experimental basis, subsequently evaluated, and the process was repeated once more. In this series of experiments, the new GCUSP algorithm, which consists of a chroma‐dependent lightness compression followed by a compression towards the lightness of the reproduction cusp on the lightness axis, gave the most accurate and stable performance overall. The results of these experiments were also useful for improving the understanding of some gamut mapping factors—in particular gamut difference between media. © 2001 John Wiley & Sons, Inc. Col Res Appl, 26, 85–102, 2001 相似文献
14.
Michael H. Brill 《Color research and application》2012,37(6):423-423
This poem summarizes the fit‐first method of camera evaluation described in Jim Worthey's “Applications of vectorial color.” The algorithm works with the locus of unit monochromats (LUM) in camera and CIE color‐matching spaces. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2011; 相似文献
15.
Gregory High;Peter Nussbaum;Phil Green; 《Color research and application》2024,49(2):272-287
A web-hosted online experiment was previously developed to find the visual difference between four reproduction gamuts using direct magnitude estimation (Proc. IS&T 29th Color and Imaging Conf, 2021:317–322). In order to increase the size of the data set, but without overburdening observers, a modular approach was adopted. The original methodology was therefore extended across 10 linked sub-experiments to make comparisons between some 36 gamuts, which were designed to exhibit a variety of different gamut shapes, contrast ratios, and substrate colors within the constraints of a desktop display. In addition to each set of test images, a common normalization set was included in all sub-experiments in order to adjust each observer's choice of modulus to a global average observer, and thus combine the results into a larger data set. Finally, an interval scale was inferred from the normalized magnitude data using a categorical judgment approach to calculate scale values. The fitted data revealed a power function close to a square-root between the interval and magnitude scales. 相似文献
16.
Xiandou Zhang Qiang Wang Jincheng Li Xiaohui Zhou Yuechuan Yang Haisong Xu 《Color research and application》2017,42(1):68-77
A new spectral reflectance estimation method based on CIE XYZ values under multi‐illuminants was proposed to obtain multi‐spectral images accurately by using digital still cameras. CIE XYZ values under multi‐illuminants were initially predicted from raw RGB responses by using a polynomial model with local training samples. Then, spectral reflectance was constructed from the predicted CIE XYZ values via the pseudo‐inverse method. Experimental results indicated that the new spectral reflectance estimation method significantly outperformed the traditional colorimetric characterization method without requiring extra training samples or greatly increasing computational complexities. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 68–77, 2017 相似文献
17.
A feasible approach to spectral color management was previously defined to include lookups performed within an interim connection space (ICS). ICS is relatively low in dimensions and is situated between a high‐dimensional spectral profile connection space and output units. The definition of ICS axes and the minimum number of ICS dimensions are explored here by considering the LabPQR, an ICS described in earlier research. LabPQR has three colorimetric dimensions (CIE L*a*b*) and additional dimensions to describe a metameric black (PQR). Several versions of LabPQR are explored. One type defines PQR axes based on metameric blacks generated from Cohen and Kappauf's spectral decomposition. The second type is constructed in an unconstrained way where metameric blacks are statistically derived based on the spectral characteristics of the target output device. For a six‐dimensional LabPQR, one that uses three colorimetric and three metameric black dimensions, it was found that Cohen and Kappauf‐based LabPQR was inferior for estimating the spectra when compared with the unconstrained method. However, when the limited spectral gamut of an output device was introduced through printer simulation and necessary spectral gamut mapping, the disadvantage of the six‐dimensional Cohen and Kappauf‐based LabPQR dissipated. On the other hand, reducing LabPQR to only five‐dimensions (two metameric black dimensions) reintroduced the advantage of the unconstrained approach even after simulated printing including spectral gamut mapping. Importantly, it was found that the five‐dimensional unconstrained approach achieved equivalent levels of performance to a full 31‐dimensional approach within simulated printer spectral gamut limitations. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 282–299, 2008. 相似文献
18.
Mohamed Abdellatif 《Color research and application》2015,40(6):564-576
The spectral overlap of color‐sampling filters increases errors when using a diagonal matrix transform, for color correction and reduces color distinction. Spectral sharpening is a transformation of colors that was introduced to reduce color‐constancy errors when the colors are collected through spectrally overlapping filters. The earlier color‐constancy methods improved color precision when the illuminant color is changed, but they overlooked the color distinction. In this article, we introduce a new spectral sharpening technique that has a good compromise of color precision and distinction, based on real physical constraints. The spectral overlap is measured through observing a gray reference chart with a set of real and spectrally disjoint filters selected by the user. The new sharpening method enables to sharpen colors obtained by a sensor without knowing the camera response functions. Experiments with real images showed that the colors sharpened by the new method have good levels of color precision and distinction as well. The color‐constancy performance is compared with the data‐based sharpening method in terms of both precision and distinction. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 564–576, 2015 相似文献
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In this work, several near‐lossless compression methods for spectral images have been analyzed and compared. These methods are based both on the principal component analysis (PCA) and on the choice of a minimum number of spectral points, selected following different criteria. The analysis, initially carried out on 14 National Physical Laboratory tiles of certified colour, has been extended to some spectral images of paintings taken at the National Gallery of Parma (Italy). The comparison of the results with those obtained by applying the PCA analysis shows that the best method indicated as “method of a few significant points” allows reducing the spectral image size of a factor of 10 without loss of spectral and colour information. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010 相似文献