A revision of CIECAM97s for practical applications

The CIE 1997 Interim Color Appearance Model (Simple Version), abbreviated CIECAM97s, was proposed by CIE TC1‐34 in 1997 in response to the needs of the imaging industry for a single, practically applicable, color appearance model for device‐independent color imaging applications. CIECAM97s has been successful in focusing a large number of researchers on a single direction to implement, evaluate, and suggest improvements for a single CIE model. However, CIECAM97s has been less successful in achieving the goal of being practically applicable. CIECAM97s remains a complex color appearance model, and this complexity seems to be somewhat of a barrier for its widespread adoption and use. CIE TC8‐01 is currently working toward recommendations for practical application of CIECAM97s. Part of TC8‐01's work is the consideration and evaluation of potential revisions and simplifications of CIECAM97s. This article incorporates several previously proposed enhancements of CIECAM97s and a few new suggestions into a revised model for the consideration of TC8‐01. It is hoped that this revision will aid in focusing ongoing model tests and perhaps be the starting point for a new CIE recommendation, once sufficient testing and perhaps further refinements are completed. © 2001 John Wiley & Sons, Inc. Col Res Appl, 26, 418–427, 2001     

A comprehensive model of colour appearance for related and unrelated colours of varying size viewed under mesopic to photopic conditions

CIE has recommended two previous appearance models, CIECAM97s and CIECAM02. However, these models are unable to predict the appearance of a comprehensive range of colours. The purpose of this study is to describe a new, comprehensive colour appearance model, which can be used to predict the appearance of colours under various viewing conditions that include a range of stimulus sizes, levels of illumination that range from scotopic through to photopic, and related and unrelated stimuli. In addition, the model has a uniform colour space that provides a colour‐difference formula in terms of colour appearance parameters. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 293–304, 2017     

CMC 2000 chromatic adaptation transform: CMCCAT2000

CMCCAT97 is a chromatic adaptation transform included in CIECAM97s, the CIE 1997 colour appearance model, for describing colour appearance under different viewing conditions and is recommended by the Colour Measurement Committee of the Society of Dyers and Colourists for predicting the degree of colour inconstancy of surface colours. Among the many transforms tested, this transform gave the most accurate predictions to a number of experimental data sets. However, the structure of CMCCAT97 is considered complicated and causes problems when applications require the use of its reverse mode. This article describes a simplified version of CMCCAT97— CMCCAT2000—which not only is significantly simpler and eliminates the problems of reversibility, but also gives a more accurate prediction to almost all experimental data sets than does the original transform. © 2002 John Wiley & Sons, Inc. Col Res Appl, 27, 49–58, 2002     

Media‐dependent color appearance modeling based on artificial neural networks

In this study, we tried to consider various color appearance factors and device characterization together by visual experiment to simplify the across‐media color appearance reproduction. Two media, CRT display (soft‐copy) and NCS color atlas (hard‐copy), were used in our study. A total of 506 sample pairs of RGB and HVC, which are the attributes of NCS color chips, were obtained according to psychophysical experiments by matching soft copy and hard copy by a panel of nine observers. In addition, a set of error back‐propagation neural networks was used to realize experimental data generalization. In order to get a more perfect generalizing effect, the whole samples were divided into four parts according to different hues and the conversion between HVC and R_HVCG_HVCB_HVC color space was implemented. The current results show that the displays on the CRT and the color chips can match well. In this way, a CRT‐dependent reproduction modeling based on neural networks was formed, which has strong practicability and can be applied in many aspects. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 218–228, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20209     

Evaluation of color matching performances for SPEM and other models

We performed subjective experiments to evaluate color matching performance of the Spectral Properties Estimation Model (SPEM) and six other models (von Kries, CIELAB, LLAB, RLAB, Nayatani, and CIECAM97s) between two CRT monitors whose whites were quite different. Moreover, we evaluated color matching of these models between a CRT monitor and a printed image set in a dark room. The SPEM we developed is a new chromatic adaptation model based on hypothetical spectral properties estimation. This article describes the subjective experiments and the results obtained. The SPEM produced good color matching performance in the experiments. The detailed algorithm of the SPEM is given in the Appendix. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 445–453, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10197     

Dynamic cone response functions for models of colour appearance

The CIECAM97s type of colour appearance models results in some changes in hue and saturation for series of colours of constant chromaticity but changing luminance factor. To keep hue and saturation constant for such series, a model in which the dynamic cone response is based on a power function has been developed. By optimizing its parameters, its correlates of hue, lightness, colourfulness, brightness, and saturation perform nearly as well as those of CIECAM97s. A similar performance is achieved in a modified power model, which is more physiologically plausible. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 82–88, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10128     

Viewing techniques for cross-media image comparisons

Several viewing techniques can be used to compare CRT images to printed images under different illuminants and luminance levels. This research examined five such viewing techniques including memory, successive-binocular, simultaneous-binocular, simultaneous-haploscopic, and successive-Ganzfeld-haploscopic viewing. The results showed that these techniques yielded different results when comparing printed originals to matching CRT reproductions, derived using various color-appearance models. Memory viewing was determined to be the most appropriate viewing technique for further study of cross-media color reproduction. © 1996 John Wiley & Sons, Inc.     

Colour appearance shifts in two different‐sized viewing conditions

This study assessed the effect of size on colour appearance, using a colour matching paradigm where two sizes were presented in a setting similar to a normal colour selection interface. Twelve colours sampling the entire range of the colour spectrum were chosen as target stimuli. The target stimuli consisted of either a large (30° by 50°) or a small (0.5° by 0.5°) test field displayed on a cathode ray tube (CRT). In the experiment, a set of small colour samples consisting of the target and its neighboring colours was presented on the screen. Fifty‐seven participants were asked to pick a colour from the sample set that appeared to exactly match the target. Results in CIECAM02 showed a consistent increase in the apparent brightness (Q) but some decrease in saturation (s) for the larger field. Hue shifts were observed to form a systematic pattern. We noticed a discernable trend showing that, for targets of bluish or purplish colour hues, the accuracy of colour matching is lower and colour difference is greater in the condition of the large viewing field. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010     

Testing the robustness of CIECAM02

CIE TC8‐01 has adopted a new color appearance model: CIECAM02¹ replaces the CIECAM97s.² The new model consists of a number of refinements and simplifications of the CIECAM97s color appearance model. This article describes further tests to the robustness of the forward and reverse modes. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 99–106, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20087     

Unique hue data for colour appearance models. Part I: Loci of unique hues and hue uniformity

Psychophysical experiments were conducted to assess unique hues on a CRT display for a large sample of colour‐normal observers (n = 185). These data were then used to evaluate the most commonly used colour appearance model, CIECAM02, by transforming the CIEXYZ tristimulus values of the unique hues to the CIECAM02 colour appearance attributes, lightness, chroma and hue angle. We report two findings: (1) the hue angles derived from our unique hue data are inconsistent with the commonly used Natural Color System hues that are incorporated in the CIECAM02 model. We argue that our predicted unique hue angles (derived from our large dataset) provide a more reliable standard for colour management applications when the precise specification of these salient colours is important. (2) We test hue uniformity for CIECAM02 in all four unique hues and show significant disagreements for all hues, except for unique red which seems to be invariant under lightness changes. Our dataset is useful to improve the CIECAM02 model as it provides reliable data for benchmarking. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2011     

Preprocessing to CIECAM02 input color with chromatic background

A preprocessing to CIECAM02 input color for color appearance prediction was proposed. In this study, 8640 color appearance matching pairs (NCS color charts with red, green, yellow, and blue backgrounds in a light booth and their reproductions with gray background on a CRT screen) were obtained by psychophysical experiment using the simultaneous‐binocular technique. Because only the lightness of background is included in CIECAM02, a color inducing vector based on opponent‐colors theory was introduced to preprocess CIECAM02 inputs, so that CIECAM02 may predict the corresponding color of an input color with chromatic background as well. By data fitting, a color preprocessing formula describing a relationship between the color inducing vector and the NCS chromaticness was conducted. Furthermore, the formula's performance was tested and the results showed that it was good for implementing the color appearance prediction of input colors with different chromatic backgrounds.© 2006 Wiley Periodicals, Inc. Col Res Appl, 32, 40–46, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20287     

Modelling of chromatic contrast for retrieval of wallpaper images

Colour remains one of the key factors in presenting an object and, consequently, has been widely applied in retrieval of images based on their visual contents. However, a colour appearance changes with the change of viewing surroundings, the phenomenon that has not been paid attention yet while performing colour‐based image retrieval. To comprehend this effect, in this article, a chromatic contrast model, CAMcc, is developed for the application of retrieval of colour intensive images, cementing the gap that most of existing colour models lack to fill by taking simultaneous colour contrast into account. Subsequently, the model is applied to the retrieval task on a collection of museum wallpapers of colour‐rich images. In comparison with current popular colour models including CIECAM02, HSI and RGB, with respect to both foreground and background colours, CAMcc appears to outperform the others with retrieved results being closer to query images. In addition, CAMcc focuses more on foreground colours, especially by maintaining the balance between both foreground and background colours, while the rest of existing models take on dominant colours that are perceived the most, usually background tones. Significantly, the contribution of the investigation lies in not only the improvement of the accuracy of colour‐based image retrieval but also the development of colour contrast model that warrants an important place in colour and computer vision theory, leading to deciphering the insight of this age‐old topic of chromatic contrast in colour science. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 361–373, 2015     

The usability of the CIE colour‐matching functions in the case of CRT monitors

During the past years, several papers have been published that question the use of the CIE colour‐matching functions in the case of metameric samples. Visually matching samples produced on CRT (Cathode Ray Tube) monitors are metameric to most colour stimuli created by illuminating reflecting materials. As CRT monitors are often used in colour design applications, it seemed important to check how well CIE colorimetry will predict such colour matches. To investigate this problem, we set up an experiment in which painted samples were matched with samples produced on a CRT monitor. The colour of incandescent lamp irradiated Munsell samples were visually matched to the mixture of the RGB primaries of a CRT monitor. Both the reflected colour stimuli of the Munsell samples and the emitted stimuli of the monitor were measured spectroradiometrically. Our results imply that there is an observer‐dependent variability among the matches, but we could not find a major difference between the tristimulus data of the hard copy and soft copy presentations that would indicate errors in the CIE colour‐matching functions. The measurement accuracy, quantization errors of the monitor, and the achieved accuracy of the colour matches are treated in this study. © 2001 John Wiley & Sons, Inc. Col Res Appl, 26, 436–441, 2001     

Comprehensive color solutions: CAM16, CAT16, and CAM16‐UCS

The CIECAM02 color‐appearance model enjoys popularity in scientific research and industrial applications since it was recommended by the CIE in 2002. However, it has been found that computational failures can occur in certain cases such as during the image processing of cross‐media color reproduction applications. Some proposals have been developed to repair the CIECAM02 model. However, all the proposals developed have the same structure as the original CIECAM02 model and solve the problems concerned at the expense of losing accuracy of predicted visual data compared with the original model. In this article, the structure of the CIECAM02 model is changed and the color and luminance adaptations to the illuminant are completed in the same space rather than in two different spaces, as in the original CIECAM02 model. It has been found that the new model (named CAM16) not only overcomes the previous problems, but also the performance in predicting the visual results is as good as if not better than that of the original CIECAM02 model. Furthermore the new CAM16 model is simpler than the original CIECAM02 model. In addition, if considering only chromatic adaptation, a new transformation, CAT16, is proposed to replace the previous CAT02 transformation. Finally, the new CAM16‐UCS uniform color space is proposed to replace the previous CAM02‐UCS space. A new complete solution for color‐appearance prediction and color‐difference evaluation can now be offered.     

Different matrices for CIECAM02

CIECAM02 has been used to predict colour appearance under a wide range of viewing conditions, to provide a uniform colour space, and to provide a profile connection space for colour management. However, some problems have been identified with CIECAM02. CIE Technical Committee 8‐11 is currently working on the methods to resolve the problems for practical applications. Part of the CIE TC8‐11 work is to repair the lightness computational failure. This article incorporates most of the previous suggestions and makes some further tests. It is hoped that this article will aid the ongoing work of the CIE TC8‐11 and perhaps be the starting point for repairing the CIECAM02 for colour management and for the new recommendation. © 2012 Wiley Periodicals, Inc. Col Res Appl, 39, 143–153, 2014     

Applying chromatic adaptation transforms to mixed adaptation conditions

A set of psychophysical experiments was conducted to investigate the state of adaptation between hardcopy and softcopy images when viewed under mixed illumination conditions. The performance of three chromatic adaptation transforms, CMCCAT97, CMCCAT2000 and CIECAT94, was compared to that of the S‐LMS, a mixed adaptation model. The adaptation ratios of each model were varied to investigate the state of adaptation of the human visual system. Printed complex images were used as originals. A series of softcopy reproduction pairs was displayed on a CRT with a D93 white point and compared to the original in an illuminated room. Three ambient lights were studied: a D50 simulator, an Illuminant A simulator and a Cool‐white fluorescence lamp. The experiments were divided into nine phases according to the changes of illuminants and the luminance levels. A simultaneous binocular matching technique was employed. Observers compared the hardcopy with a given pair of softcopies and identified which reproduction was the closer colour match. The results showed that the state of adaptation of the human visual system was between 40–60% adapted to the white point of the monitor regardless of the changes in illumination conditions. The overall results showed that CMCCAT2000 with proper adaptation ratio outperformed the other models and could be applied to mixed adaptation conditions. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 436–444, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10196     

Prediction of Munsell appearance scales using various color‐appearance models

The chromaticities of the Munsell Renotation Dataset were applied to eight color‐appearance models. Models used were: CIELAB, Hunt, Nayatani, RLAB, LLAB, CIECAM97s, ZLAB, and IPT. Models were used to predict three appearance correlates of lightness, chroma, and hue. Model output of these appearance correlates were evaluated for their uniformity, in light of the constant perceptual nature of the Munsell Renotation data. Some background is provided on the experimental derivation of the Renotation Data, including the specific tasks performed by observers to evaluate a sample hue leaf for chroma uniformity. No particular model excelled at all metrics. In general, as might be expected, models derived from the Munsell System performed well. However, this was not universally the case, and some results, such as hue spacing and linearity, show interesting similarities between all models regardless of their derivation. © 2000 John Wiley & Sons, Inc. Col Res Appl, 25, 132–144, 2000     

Testing the performance of CIECAM02 from 100 to 3500 cd/m2

Color appearance models were developed to characterize the color attributes of stimuli under different viewing conditions based on data collected through magnitude estimation or color matching experiments. Although human beings experience very high light levels under daylight and the reproduction of colors under daylight is important in the color and imaging industries, the existing color appearance models were developed based on the data that were collected under the conditions with luminance levels below 700 cd/m² due to the lack of facilities to produce stable illumination at high light levels. A recent study investigating color preference of an artwork under a wide range of light levels from 20 to 15 000 lx suggested that CIECAM02 cannot accurately characterize the color appearance under extremely high light levels. This study was designed to directly test the performance of CIECAM02 from 100 to 3500 cd/m². Human observers performed color match for four hues under a series pairs of adapting conditions with a haploscopic viewing condition. It was found that CIECAM02 had the best performance in characterizing the hue angles but the worse performance in characterizing the brightness with a maximum underprediction around 200% across a wide range of luminance. This was mainly due to the fact that CIECAM02 was developed based on the data collected under relatively low adapting luminance levels. The color appearance model that was proposed to use the adapting luminance levels in characterizing the cone compression in the postadaptation process was found to have a much better performance in characterizing the brightness.     

Proposed modification to the CIECAM02 colour appearance model to include the simultaneous contrast effects

A modified CIECAM02 colour appearance model, named CIECAM02‐m2, is proposed to enable CIECAM02 to predict the simultaneous contrast effect. The structure of the CIECAM02‐m2 is a development from CIECAM02, and contains two different procedures for modifying the reference white; one is for lightness and the other is for hue. The model was tested using a data set accumulated in this study and the LUTCHI data. The CV values for three colour attributes between predictions and experimental data were used to evaluate the accuracy of the model. The low CV values obtained show the performance of the CIECAM02‐m2 model to predict the simultaneous contrast effect satisfactorily. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 121 – 129, 2007