CIECAM02 Color Appearance Research Articles

Extending CIECAM02 and CAM16 for the Helmholtz–Kohlrausch effect

AbstractIncreasing the purity of a visual stimulus increases its brightness, even if the stimulus luminance is held constant. This perceptual phenomenon is known as the Helmholtz–Kohlrausch (H–K) Effect. This paper reviews published experimental data and models of the effect. Using past experimental data, we derive a modification of the CIECAM02 and CAM16 color appearance models to account for the H–K effect and compare the proposed model to other models. Finally, we discuss the need for further experimental data on the H–K effect to refine the proposed model.

Brightness, lightness, colorfulness, and chroma in CIECAM02 and CAM16

AbstractIn the CIECAM02 and CAM16 color appearance models, brightness is computed as a nonlinear function of lightness. This paper traces the history of that nonlinearity to its roots in the Hunt color appearance model. A new, more robust, linear relationship between lightness and brightness is proposed. This new formula also prompts the reevaluation of the CAM16 equations for chroma, colorfulness, and saturation. The new formulas for these perceptual attributes are tested on experimental data from the Munsell color order system and the LUTCHI color appearance dataset and are compared to the performance of the original CAM16 equations.

Lightness And Luminance: Perceptual Qualities in Conditions Of Simultaneous Contrast

This article is devoted to the research of the influence of induction and crispening effects on the lightness of objects. The target of this research is to simplify and clarify the analysis of the light distributions derived from the results of lighting calculations and measurements, and also to form the recommendations for obtaining preferred lightness contrasts in the case of visual perception of objects on different backgrounds. To provide such possibilities, it is necessary to refine the model of the lightness calculation in modern colour appearance models, which, in turn, requires the results of new experiments to take into account the induction and crispening effects in the conditions of simultaneous contrast. The same experiment was established by Takasaki on visual perception of grey squares on grey backgrounds. The article substantiates the necessity to refine the results of the Takasaki experiment and conduct the new experimental approach in more strictly specified conditions and in the expanded luminance range to ensure conditions of the modern standards. Here we propose setting up an experiment that provides these refinements and considers the properties of the proximal field – the contour of objects. The search of the results uses multi-objective optimization methods. The first results of this experiment are presented, based on them, were formed proposals to determine the preferred luminance of objects to ensure the required levels of lightness contrast when working on specified backgrounds. The calculations of the lightness deviations obtained as the result of the experiment and in the CIECAM02 colour appearance model, are presented. The peculiarities of translations of lighting engineering literature in the field of modelling a light-colour environment are noted, which require clarification for a correct and reliable understanding of colour appearance models, for which is proposed to open a discussion on this subject.

Does CIECAM02 color appearance model work well for fluorescent samples?

AbstractIn this work, the validity of a chosen color appearance model, CIECAM02 is examined for perceived lightness and brightness of fluorescent samples against some near achromatic backgrounds. To this end, the visual assessment technique and the paired comparison method have been conducted and the results are compared to those obtained by CIECAM02 color appearance model. Opposed to the initial expectation, the results show that the CIECAM02 is not an adequate model for prediction of lightness and brightness of fluorescent samples over a set of gray backgrounds.

Visualizing the trade-offs between laser eye protection and laser eye dazzle

Visual detection and color discrimination become more challenging tasks when laser eye protection (LEP) is worn. This is due to the reduced light transmission and wavelength-blocking characteristics of LEP filters. LEP can, however, provide valuable protection against laser eye dazzle—the temporary reduction of vision caused by visible wavelength lasers. To understand this compromise, a model has been developed to allow the visual impacts of LEP to be simulated and balanced against their dazzle protection capabilities. This model is able to use any digital image as a background scene, allowing for real-world visualizations of LEP and dazzle over a broad range of scenarios. The work is built from the CIECAM02 color appearance model and a modified CIE general disability glare equation, together with experimentally validated adjustments to improve the accuracy of this application. The resulting model will help to inform LEP procurement and will serve as an educational tool for LEP users.Visual detection and color discrimination become more challenging tasks when laser eye protection (LEP) is worn. This is due to the reduced light transmission and wavelength-blocking characteristics of LEP filters. LEP can, however, provide valuable protection against laser eye dazzle—the temporary reduction of vision caused by visible wavelength lasers. To understand this compromise, a model has been developed to allow the visual impacts of LEP to be simulated and balanced against their dazzle protection capabilities. This model is able to use any digital image as a background scene, allowing for real-world visualizations of LEP and dazzle over a broad range of scenarios. The work is built from the CIECAM02 color appearance model and a modified CIE general disability glare equation, together with experimentally validated adjustments to improve the accuracy of this application. The resulting model will help to inform LEP procurement and will serve as an educational tool for LEP users.

An Analysis of the DisplayHDR Compliance Specification and Its DisplayHDR True Black Specification Extension

AbstractThe VESA DisplayHDR High‐Performance Monitor and Display Compliance Test Specification, along with its extension for emissive pixel displays–DisplayHDR True Black, create a minimum acceptance level for HDR performance in monitors, notebooks, and all‐in‐one computer products. Here, we examine associated specifications tests, while quantifying performance against the CIECAM02 color appearance and SEMI Perceptual Contrast Length models.

Entrainment to the CIECAM02 and CIELAB colour appearance models in the human cortex

In human visual processing, information from the visual field passes through numerous transformations before perceptual attributes such as colour are derived. The sequence of transforms involved in constructing perceptions of colour can be approximated by colour appearance models such as the CIE (2002) colour appearance model, abbreviated as CIECAM02. In this study, we test the plausibility of CIECAM02 as a model of colour processing by looking for evidence of its cortical entrainment. The CIECAM02 model predicts that colour is split in to two opposing chromatic components, red-green and cyan-yellow (termed CIECAM02-a and CIECAM02-b respectively), and an achromatic component (termed CIECAM02-A). Entrainment of cortical activity to the outputs of these components was estimated using measurements of electro- and magnetoencephalographic (EMEG) activity, recorded while healthy subjects watched videos of dots changing colour. We find entrainment to chromatic component CIECAM02-a at approximately 35 ms latency bilaterally in occipital lobe regions, and entrainment to achromatic component CIECAM02-A at approximately 75 ms latency, also bilaterally in occipital regions. For comparison, transforms from a less physiologically plausible model (CIELAB) were also tested, with no significant entrainment found.

Background luminance and subtense affects color appearance

AbstractTwo psychophysical experiments were conducted to investigate the color appearance under non‐uniform surround conditions with variation of stimulus luminance, surround luminance, background luminance, background orientation, and background size. The results show that the background size and surround luminance influence the appearance intensively, but that the orientation of background pattern has little effect. A method to determine optimal parameters for the CIECAM02 color appearance model in lighting applications is proposed. An UGR‐based model also is optimized for brightness estimation. The luminance of adapting field can be estimated by Gaussian‐like functions. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 440–449, 2017

Real‐time video chroma keying: a parallel approach based on local texture and global colour distribution

This study presents an automatic, human perception based chroma-keying algorithm that extracts the objects of interest (i.e. foreground) from monochromatic background. Given an image to be chroma keyed, the global colour distribution and the local texture property are analysed in CIECAM02 colour appearance model. After the analysis, input image is automatically segmented into three parts: foreground, background, and uncertain regions. Afterwards, the background colour is propagated from known background to uncertain region by using interpolation functions; and the foreground colour is estimated based on global colour distribution and a linear cost criteria. The quantitative and perceptual comparisons on the matting results show that the proposed method can reliably remove the background region, correctly restore the intrinsic foreground colour, and accurately keep the fine details. In addition, the authors implement the proposed method on a heterogeneous parallel computing architecture which efficiently distributes the workload among different processors. The simulation results show that the foreground objects can be accurately extracted from high-definition and/or ultra-high-definition videos in real time.

Indoor lighting quality: Effects of different wall colours

This paper reports the results of measurements performed in a test room to investigate the impact of using different wall colours and light scenes on indoor lighting quality. Eye level spectral irradiances were measured for a user located inside the room and seated at a desk. These measurements allow the use of the Irradiance Toolbox, which makes it possible to calculate equivalent illuminances for the photopigments in the human eye. Moreover, the CIECAM02 colour appearance model was used to investigate the variations in hue and chroma values of the different wall colours when changing the light scene. The results demonstrate that there are significant variations in eye level spectral irradiance distributions, photoreceptor stimulation and hue and chroma values with different combinations of wall colours and light scenes.

Unique hue data for colour appearance models. Part III: Comparison with NCS unique hues

AbstractIn this study, Swedish Natural Color System (NCS) unique hue data were used to evaluate the performance of unique hue predictions by the CIECAM02 colour appearance model. The colour appearance of 108 NCS unique hue stimuli was predicted using CIECAM02, and their distributions were represented in a CIECAM02 ac–bc chromatic diagram. The best‐fitting line for each of the four unique hues was found using orthogonal distance regression in the ac–bc chromatic diagram. Comparison of these predicted unique hue lines (based on the NCS data) with the default unique hue loci in CIECAM02 showed that there were significant differences in both unique yellow (UY) and unique blue (UB). The same tendency was found for hue uniformity: hue uniformity is worse for UY and UB stimuli in comparison with unique red (UR) and unique green (UG). A comparison between NCS unique hue stimuli and another set of unique hue stimuli (obtained on a calibrated cathode ray tube) was conducted in CIECAM02 to investigate possible media differences that might affect unique hue predictions. Data for UY and UB are in very good agreement; largest deviations were found for UR. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 256–263, 2015

Optimized flash light-emitting diode spectra for mobile phone cameras

Flash light-emitting diodes (LEDs) of modern mobile phones lack red and cyan spectral parts, however, the color gamut of their respective displays has increased in recent years. The influence of this discrepancy on the color reproduction of smart phones is investigated in this paper. Based on the CIECAM02 color appearance model, a metric is introduced to judge color reproduction of mobile phones under flash LED illumination. An evaluation method is established to compare the visual appearance of a scene under various surrounding illuminations with the reproduction of that scene. To facilitate a comparison with measurements, the evaluation method is based on the raw data of two test cameras and a Digital ColorChecker SG. To reduce the color shift between perception and reproduction, optimized flash LED spectra are presented. A single-LED and a double-LED concept with adjustable color temperature are derived from these results. Additionally, the common characteristics of flash LED spectra giving good results is investigated, identifying the spectral parts with the most influence on camera color reproduction and showing the spectral parts not contributing or even resulting in poor color reproduction. Finally the efficiency of optimized flash LED spectra is compared to standard flash LEDs.

Mathematical approach for predicting non-negative tristimulus values using the CAT02 chromatic adaptation transform

It has been reported that for certain colour samples, the chromatic adaptation transform CAT02 imbedded in the CIECAM02 colour appearance model predicts corresponding colours with negative tristimulus values (TSVs), which can cause problems in certain applications. To overcome this problem, a mathematical approach is proposed for modifying CAT02. This approach combines a non-negativity constraint for the TSVs of corresponding colours with the minimization of the colour differences between those values for the corresponding colours obtained by visual observations and the TSVs of the corresponding colours predicted by the model, which is a constrained non-linear optimization problem. By solving the non-linear optimization problem, a new matrix is found. The performance of the CAT02 transform with various matrices including the original CAT02 matrix, and the new matrix are tested using visual datasets and the optimum colours. Test results show that the CAT02 with the new matrix predicted corresponding colours without negative TSVs for all optimum colours and the colour matching functions of the two CIE standard observers under the test illuminants considered. However, the accuracy with the new matrix for predicting the visual data is approximately 1 CIELAB colour difference unit worse compared with the original CAT02. This indicates that accuracy has to be sacrificed to achieve the non-negativity constraint for the TSVs of the corresponding colours. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2011

Progress in the Theory Studies of CIECAM02

In 2002, TC8-01 launched the CIECAM02 color appearance model and determined it as recommendation for industrial applications. In this paper, we review the situation and the latest theoretical research progress about CIECAM02 and discuss the main theoretical issues from three aspects , uniformity, model defects, prediction improvement, finally we analyze its shortcomings and put forward the problem to be solved and some research directions.

Robust Spectral Implementation of High-Fidelity Printer Characterization for Cross-Media High-Dynamic-Range Imaging Applications

This research introduces a multi-spectral type of High-Fidelity (Hi-Fi) colorant color separation algorithm for printing/printer system using more than four inks (colorants). This Hi-Fi colorant separation algorithm, derived for six-colorant CMYKOG printer systems, finds the best colorant combination to reproduce spectra of every color, concerned in high-dynamicrange of original images for an accurate color-matching or – reproduction application. This work revised and extended a previous research, which carried out a seven-ink of CMYKRGB FM printing characterization of presses, only used in the conventional Graphic Arts. An Epson 9900 inkjet printer, having the capability of a six-colorant set, CMYKOG, was spectrally characterized for High-Fidelity (Hi-Fi) multi-color printer simulation. The superset of CMYKOG was divided into three subsets, including two five-colorant groupings of CMYKO and CMYKG, and one four-colorant grouping of CMYK. The spectral printer characterization applied a polynomial regression approach with singular value decomposition method (SVD). The mean ΔE*00 values were 0.98∼1.17 and 1.06∼1.33 found in the forward and the reverse processes respectively. Also 0.0008 ∼ 0.0011 and 0.0009 ∼ 0.0024 of the mean RMSE values were obtained for the forward and the reverse spectral transform respectively. It implies the spectral reflectance of every color in test datasets was satisfactorily reconstructed. Moreover, to robustly perform a feasible approach of spctral color management for Hi-Fi printer simulation in cross-media color reproduction system, a GUI-based of HDR (High-Dynamic-Range) image-fusion module were also be introduced to produce original HDR complex color images. It integrated algorithms of: 1) a multi-raw-processed-image fusion process based on both luminance and gray-balancing strategies; 2) a multiple-conversing-points type of gamut-mapping; 3) Adaptive Multi-illuminants white-balancing; 4) the CIECAM02 color appearance modeling; 5) a Gaussian pyramid type of image enhancement; and 6) a logarithmic HDR tone mapping; and finally an ideal simulated CIEXYZ type of spectra sensing model which adopts interim AdobeRGB connection reference space, combined with CIE 1931 2° standard observer. Consequently, a robust spectral type of cross-media color reproduction system, based on a colorimetric approach of HDR and Hi-Fi (High-Fidelity) was implemented in the study.

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

AbstractPsychophysical 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

Changes in colour appearance of a large display in various surround ambient conditions

AbstractThis article focuses on the change in colour appearance of a large display arising from various illumination conditions. Nine experimental phases were conducted according to different surround conditions including dark, indoor, and outdoor conditions. Each of the presented test colours was assessed by 10 observers using a magnitude estimation method. The surrounds used in all phases were divided into two groups: excluding and including veiling glare. Additionally, the effect due to different sizes of both stimuli and surround was investigated. Diverse visual effects were examined and reported. Finally, the visual colour appearance data were used to test the CIECAM02 colour appearance model. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010

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

AbstractA 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

Expanding display color gamut beyond the spectrum locus

AbstractDigital video and display media are at a “sweet spot” of growth with brighter and more colorful digital projectors and displays available seemingly every day. Much more is possible in achieving brighter and more vibrant colors, colors that may even transcend our typical experience in terms of dynamic range and an expanded gamut in the perceptual sense. If the full capabilities of these technologies to produce a fuller visual experience are to be realized, new processing and encoding methodologies are required. In this article, the powers of adaptation and the CIECAM02 color appearance model are exploited to define perceptual gamut. The strategy of this methodology is, simply and in effect, to “push down” the white point of the display and demonstrate, both empirically and with a limited set of images, a striking gamut expansion in the perceptions of lightness, chroma, brightness, and colorfulness beyond the locus of pure, spectral color, and the MacAdam limits as observed with traditional display configurations. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 475–482, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20260

Effect of DLP projector white channel on perceptual gamut

Abstract— The effect of white‐channel enhancement as implemented in the Texas Instrument DLP™ digital projector technology is evaluated theoretically using both the CIELAB and the CIECAM02 color appearance models and experimentally through psychophysical testing using real images. Both theory and test results confirm a compression of perceptual gamut in both chroma and colorfulness as a result of the added white channel. Hence, while this technology is ideal for viewing graphics and text under ambient conference‐room conditions where lightness contrast is important, it is necessarily less than ideal for viewing images or in home‐theater environments where color is important.