Color tolerance study on white in practical aspect: Perceptibility versus acceptability

This study investigates how the color tolerance for whites is affected by color category and context. Two experiments with different contexts, perceptibility or acceptability, were conducted using 27 color variation samples from six color categories (Neutral‐White, Red‐White, Yellow‐White, Green‐White, Blue‐White, and Blue‐Vivid). The results indicated that the color tolerance for Green‐white is dominantly higher relative to the other white‐based colors, whereas the color tolerance for Yellow‐White and Neutral‐White are relatively lower. However, contrary to the hypothesis, no significant differences in the level of color tolerances could be found between the two context of perceptibility and acceptability. The color tolerance thresholds for each color category groups in both experiments were similar. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 582–588, 2014     

Color preference of aged observers compared to young observers

In modern society, elderly people tend to become enthusiastic users of displays. These displays are optimized for the visual properties of young adults ignoring the specific attributes of the vision of the elderly though the existence of differences is evident. It is true, however, that most of the investigations follow a bottom‐up paradigm (changes of optical density, neural changes, etc.), and their results are too ambiguous to be taken into account directly in display optimization for the elderly, partly because there is a long‐term adaptation, which apparently recompensates for some of the changes in the human visual system. Preference is a high‐level psychological factor having a very important impact on the acceptability of color displays. The present article follows a top–down methodology to investigate these age‐related differences directly. The first part concentrates on functionalities of the human visual system: white point preference, chroma perception, unique, and preferred hues. Results confirm the long‐term compensation theory for the elderly observers along with the chromatic content decrease of perceived colors. The second part investigates preference differences in case of photorealistic images in terms of global and local contrast, white point, average chroma, and the effect of several image color manipulation techniques. Results indicate significant differences between young and aged observers' color image preference, some of which can be explained with neuro‐physiological changes, others may be attributed to cultural implications. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 381–394, 2008     

网络出版中文字背景色的优化

网络出版的阅读基于屏幕显示,不同于纸质出版,显示屏幕上呈现文字信息可不拘泥于白色背景。实验针对不同字体和字号的黑色文字,设计了亮白和红、黄、绿、蓝、品红、灰等不同色相的背景颜色,并在一定范围内改变其明亮度和彩度。视觉观测结果表明,因屏幕自发光的亮度很大,其最亮的白色并不适于黑色文字的显示,适合的白色背景是明亮度降低后的一定范围内的灰色。类似地,其他所实验的彩色,适于作为背景色的明度和彩度也都有一定的范围。就适于的范围大小比较而言,包括灰色在内,灰色、黄色、绿色和蓝色的明度范围明显大于红色和品红色;绿色、黄色和蓝色的彩度范围也明显大于红色和品红色,其中绿色的彩度范围尤为宽泛。     

Changes in hue and saturation of chromatic lights presented in the peripheral visual field

The perception of ten different colors on a CRT display presented across the horizontal meridian of the visual field were measured to determine the range of relevant test stimuli for color zone map measurement. Hue and saturation judgments were used based on the opponent‐colors theory. The changes of the unique hue components for eccentric displays of red, yellow, green, and blue fall within the distribution range of previous results obtained using monochromatic lights. Chromatic displays of nearly unique hues with high saturation would be significant as test colors for measurement for a color zone map. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 413–424, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10194     

Improving color reproduction accuracy of an OLED‐based mobile display

For improving color reproduction accuracy of mobile displays, we recently developed a generic model for device‐specific display characterization model that also accounts for the influence of illuminance from ambient light. In the present article, this MDCIM model (Mobile Display Characterization and Illumination Model) is applied to a Samsung Galaxy S4 display, representing OLED displays. The performance of the model was tested by determining the values of all model parameters using publicly available technical data only. We organized visual tests under various ambient illuminance levels from 600 to 3000 lux. Seven observers compared the color of displayed images with the color of physical samples. With the MDCIM method, the quality of the color match was shown to improve considerably as compared to using only device‐independent encoding color space. On a five‐point scale to quantify color reproduction accuracy, the MDCIM resulted in more than 1 unit improvement at 1000 lux illuminance. At lower and higher illuminance, the improvement was even larger. Color reproduction accuracy was found to be at least reasonable, according to the subjective assessment of visual observers, for more than 75% of the samples when using the MDCIM method, but only 20% or less when using the common device‐independent encoding color space.     

Color breakup visibility thresholds for 2‐field sequential colors

Nowadays local primary desaturation has been proved to be an effective method to suppress the color breakup for field‐sequential‐color (FSC) displays. However, little attention has been focused on the interaction between various subfield colors and the color breakup visibility. In this article, a perception experiment was conducted with the help of a 120 Hz 2‐field FSC display to investigate the thresholds of color breakup visibility along different hue directions with a constant white point in the standard color space. The experimental results show that the color breakup visibility is various when using different subfield colors for temporal combination. A relative high threshold value or low sensitivity of color breakup visibility can be observed when subfield colors are chosen along the blue‐yellow direction while becoming perceptible easily along magenta‐cyan direction. The results and analysis of our experiments are promising to optimize the performance of local primary desaturation. Meanwhile, other applications using the temporal color fusion such as tunable lighting can also benefit from the conclusion of our work to suppress the color breakup effect.     

Expanding display color gamut beyond the spectrum locus

Digital 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     

A multi-primary empirical model based on a quantum dots display technology

In this work, we built a multi-primary display model based on the new quantum dots (QD) technology to enlarge the display color gamut. In this way, first the emission spectral radiance curves of the three RGB channels of a commercial QD display were fitted to a four-parameter function. From this modeling, it is possible to gain new theoretical color primaries by selecting new spectral peaks (cyan, yellow, magenta, and/or additional RGB primaries) and imposing some colorimetric conditions for the resulting white of this proposed theoretical multi-primary display. Proper characterization to assess the performance of the display was conducted to know if the basic “gain-offset-gamma” (GOG) model can be used for direct and inverse color reproduction (from RGB to CIE-XYZ, and vice versa). The GOG model was found to well characterize this display. The spatial uniformity of the display was also evaluated in luminance and color chromaticity terms. Finally, with the primaries modeling and color characterization based on the GOG model, a 5-primary model (RGBYC) was tested. The evaluation of this theoretical RGBYC display model confirms the gamut enlargement, which can also improve goniochromatic color reproduction.     

Estimating black‐level emissions of computer‐controlled displays

It is quite common for computer‐controlled displays to emit light in image areas set to digital values of zero, referred to as their black level. This is expected for liquid–crystal displays and also can occur for cathode‐ray tube displays when the “brightness” (gun‐amplifier offset) is set excessively high. For either display, the light emission at the black level results in color channels whose chromaticities vary with luminance level. Consequently, typical methods of colorimetric characterization result in large error. When this black‐level emission is measured and accounted for suitably, characterization accuracy is dramatically improved. Unfortunately, many instruments used to measure displays have too low a sensitivity to measure black‐level emission with sufficient precision and accuracy. A method of estimating black‐level emissions was derived and tested. Because the optimal black‐level results in channel chromaticities that are invariant to the greatest extent with luminance level, an objective function was defined as the sum of chromaticity variances of each channel over a range of measurements. Minimizing this objective function resulted is an estimate of a display's black level. The estimated black level resulted in equivalent or superior performance to direct measurements. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 379–383, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10181     

Influence of repeated firings on the color parameters of two different all‐ceramic materials

All‐ceramics materials have been widely used in dental practice due to advantages of esthetic outcome. Color parameters, one of the major factors for the esthetic outcome, are affected from different factors such as repeated firings, chemical composition and thickness. In clinical practice, ceramics were frequently subjected to the repeated firings, but the effects of the repeated firings on the color parameters have been underestimated or unknown, so the aim of the study was to evaluate the effects of the repeated firings on the color parameters of all‐ceramic materials. Two commercially available A2 shaded all‐ceramic systems were used in this study (lithium disilicate pressable ceramics and computer aided design/computer aided manufacturing [CAD/CAM] fabricated zirconia). Ten samples for each group (zirconia and lithium disilicate) were prepared and subjected to repeated firings, respectively (1st, 3rd, 5th). Color measurements were performed after each repeated firings using a colorimeter (Minolta CR 321, Konica Minolta, Tokyo, Japan). The perceptibility threshold and acceptability threshold for color changes (ΔE₀₀) was defined as 0.8 and 1.8, respectively. Statistical analysis of the results was performed by using repeated measures ANOVA for color parameters and using non‐parametric Kruskal‐Wallis and Mann‐Whitney‐U test for ΔE₀₀ values (P < .05). L*, a* values showed statistically significant differences for lithium disilicate pressable ceramics and were not significant the zirconia specimens. ΔE₀₀ values were above the perceptibility level for both lithium disilicate and zirconia specimens. Repeated firings affect the color parameters of the lithium disilicate specimens. As a result of repeated firings, lithium disilicate ceramics become lighter and greener.     

Preference for luminance uniformity of refrigerator lighting

We investigated minimally required uniformity of refrigerator lighting for comfortable use while maintaining the perceived lighting quality. Two experimental conditions were set depending on having or not having the storage items. In both conditions, 12 luminance uniformity levels were provided in a refrigerator. A total of 33 women participated and assessed the lighting stimuli to judge the perceptibility and acceptability of the presented uniformity levels. As a result, the stored items influenced both the perceptibility and acceptability of the luminance uniformity. To be specific, at least 71% luminance uniformity is recommended to be acceptable, and 80% luminance uniformity is recommended to be perceived as homogeneous for refrigerator lighting. The empirical result conforms to the uniformity guideline of 70% as the minimum, implying it as a minimally requested uniformity of spatial lighting to be considered in lighting design.     

An Investigation into the Alleged Bias of Textile Shade Passers

An ANLAB colour difference equation of the type- has been applied to one set of perceptibility and three sets of acceptability data. The optimum values of l, c and h show that the equation overestimates the perceptibility of both chroma and hue differences relative to lightness differences. Significantly different weighting factors were found for the acceptability data, probably indicating that textile shade passers are biased against chroma and hue differences.     

Visual determination of hue suprathreshold color‐difference tolerances using CRT‐generated stimuli

Suprathreshold hue color‐difference tolerances were measured at four color centers using CRT‐generated stimuli. The tolerances, defined using CIELAB, were measured using two different methods of presentation. In the Absolute Experiment, the stimuli were presented at luminance levels that matched those of the previous object‐color experiments, so that the CRT stimuli were nearly metameric to the originals. In the Relative Experiment, the white point of the monitor was defined as L* = 100 at a corresponding chromaticity to the object‐color viewing environment, but at a lower luminance level. The results from these two experiments followed the same general trends; however, they were significantly different from each other for three of the four color centers. The same trends were seen in the object‐color results, although neither CRT experimental condition produced tolerances that were conclusively more similar to the object‐color results than the other. The feasibility of the use of the CRT has been demonstrated. It is likely that parametric effects of stimulus presentation are the cause of the differences in results among the different experiments, as opposed to differences in the mode of appearance. These parametric effects can be studied more quickly and economically using a computer‐controlled CRT display. © 1999 John Wiley & Sons, Inc. Col Res Appl, 24, 164–176, 1999     

Using discrete optimization for designing dental shade guides

A key criterion in the design of dental shade guides used for matching tooth color is that the shade tabs cover the natural tooth color space as completely as possible with a manageable number of tabs. Earlier studies have designed hypothetical shade guides from a given population of tooth colors described in the CIELAB system using the goal of minimizing the mean coverage error. In this study, we investigate this topic using the goal of maximizing coverage, meaning that as many measured colors as possible were within a given color difference from the nearest shade tab of the guide. We use techniques of linear discrete optimization to determine the positions of the shade tabs and consider both color difference formulas, CIELAB and CIEDE2000, in an exemplary tooth color population. We obtain coverage error and coverage figures for hypothetical shade guides of various numbers of tabs designed with the goal of either minimizing coverage error or maximizing coverage. Results show that discrete optimization and the goal of maximizing coverage could be used to improve shade guide development. The described technique could be used not only for dental shade guides development, but also for any purpose requiring coverage of as many colors as possible while keeping the number of reference colors manageable. © 2009 Wiley Periodicals, Inc. Col Res Appl, 2010     

Quantitative representation of floral colors

Human and insect pollinator perceived floral colors of 81 species of angiosperms (flowering plants) from Trivandrum (Kerala, India) was represented using the CIE 1976 L*a*b* color space and color hexagon, respectively. The floral color difference among human perceived red, yellow, and blue‐hued flowers and that of each flower from its respective pure hue was calculated using the CIE ΔE 2000 formula. Human perceived floral color difference values were consistently higher than 3.5, indicating the uniqueness of floral colors. Flowers perceived red and yellow by humans were dominant and of comparable proportions. Insect pollinators perceive most of the flowers as blue‐green. Quantitative representation of human and pollinator perceived floral colors would be invaluable to understand the information broadcasted by flowers. It can form the basis of flower grading in the floriculture industry and underpin objectivity in evolving the framework for national pollinator strategies.     

Colorimetric characterization of a computer‐controlled liquid crystal display

A new method was used to characterize computer‐controlled liquid crystal displays (LCDs). The characterization, which was performed to enable colorimetric image display, included channel independence, spatial independence, screen uniformity, and colorimetry. The colorimetric model consisted of three one‐dimensional look‐up tables (LUTs) describing each channel's optoelectronic transfer function and a 3 × 4 matrix transformation that included black‐level flare. The matrix coefficients were estimated statistically by minimizing the average CIEDE2000 color difference for a data set sampling the display's colorimetric gamut. The LUTs were recreated dynamically throughout the optimization of the matrix coefficients. The characterization was implemented with three different instruments to evaluate the robustness of the method with respect to measurement uncertainty. The average performance ranged between 0.1 and 0.4 ΔE₀₀ and was well correlated with instrument precision. The optimization approach improved performance by a factor of two compared with direct measurements. Despite differences in instrument design, the chromaticities of each primary following optimization and black‐level flare compensation were very similar. This excellent performance was a result of the display's optoelectronic properties well matching the model assumptions. The technique was also used to characterize three additional LCD displays ranging in their matching of the model assumptions. In this case, performance worsened. For one display, more complex models would be required for colorimetric characterization. Finally, a colorimetric characterization based on measurements at the center of the display and perpendicular to the face was used to predict measurements at the edges and at different angles. The results indicated that characterizations would be required at multiple positions and angles in order to achieve sufficient accuracy. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 365–373, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20046     

Development and evaluation of gamut extension algorithms

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     

Recognized visual space of illumination: A new account of center‐surround simultaneous color contrast

Appearances of an object color in a space are determined by a cortical representation of illuminant for a space or the recognized visual space of illumination (RVSI). The simultaneous color contrast phenomenon on a simple center‐surround configuration can be explained by RVSI. It is hypothesized that our visual system constructs an RVSI on the surround and then that RVSI determines color appearance of the center test. If this is correct, the color contrast can be quite strong when the surround is enlarged to be an enclosed space. To support the hypothesis, color appearance of a physical gray test was measured in a green surround of various sizes. Observers were asked to do elementary color naming in the first experiment. The results showed same tendency for all observers: once the surround was extended to walls, a ceiling, and a floor of a box, perceived chromaticness abruptly increased. In other words, three‐dimensional surround evoked strong simultaneous color contrast. In the second experiment the matching method was employed with the green and other three surround colors: red, blue, and yellow. The results were consistent with the first experiment. The well‐known color contrast is thought to be a weak version of this color change. It suggested that RVSI plays an important role in the well‐known color contrast demonstration on two‐dimensional planes. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 255–260, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20019     

数字中间片后期制作中的色彩管理

在色彩管理中使用LUT具有相当大的潜在应用价值。LUT是一个简单的数据结构,它把每一个输入值映射到相应的输出值,并且还可以确定视频硬件里每帧图像中每一个像素的数据值的大小。模仿和校正LUTs提供的转换,不但能保证多种显示器之间的匹配,而且在后期制作过程中还可以使显示的图像与胶片完美的匹配。介质中呈现的色彩组叫做色彩范围。电影正片的色彩范围与数字显示器的色彩范围具有不同的特性。数字中间片(DI)工艺有2种不同的图像编码方法:一种是使用DPX文件,其作用是进行输入和输出及表示底片密度,预览画面则需要显示LUT;另一种方法是不使用LUT而直接显示图像数据。图像数据显示的是显示器的色彩范围,而不是胶片的色彩范围。在记录到胶片上之前,数据需要转换成密度值。在制作DI过程中,可以模仿洗片厂配光工序,通过调节印片光号进行的色彩校正。本文从8个方面较详细的叙述了制作数字中间片时的色彩管理。     

Color composition features in modern architecture

The color composition in modern architecture has been often characterized in a simplistic manner. In fact, this is a complex phenomenon to be studied because of the disparity of proposals and the uniqueness of the architects involved. This research starts with a comparative study of three of the most relevant color composition systems in the first half of the 20th century (Purism and Le Corbusier, Expressionism and Taut, Neoplasticism and Rietveld), and aims to find common characteristics among them, discussing the validity of some widespread ideas about it, such as the prominence of white hues, the use of ”flat colors,” or the conception of color during the ideation phase. We propose and demonstrate three principles that are not categorical about the color composition in modern architecture: it limits the variety of hues; it not only uses white color but also displays color to conform shapes and to transform them; color has ethical connotations and not only aesthetic ones. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2011