Reading from color displays: a psychophysical model

We have investigated the effects of chromatic and luminance contrast on reading colored text on multicolor displays. Stimuli were defined in a color space with three cardinal axes. Two of these axes are chromatic and maximally modulate the opponent mechanisms of color vision; the third is an achromatic axis. We measured detection and discrimination of words and nonwords. The results show that near-perfect reading at equiluminance is possible and that in terms of machine units, luminance differences are more salient than purely chromatic differences, but these differences disappear when the discrimination data are scaled for detection threshold.     

Color blindness and a color human visual system model

A physiologically motivated human color visual system model which represents visual information with one brightness component (A) and two chromatic components (C₁ and C₂) is used to create stimuli for testing the color perception of deuteranomalous trichromats. Two experiments are performed. Using simple ramp patterns, the first experiment finds that three deuteranomalous trichromat test subjects can distinguish variations only in the C₂ component of the color vision model. This finding is further tested in the second experiment: a set of paired comparison preference tests. Two altered versions of each of three natural color images are prepared by setting either one of the color components to a constant over the full image. Pairs of an original and a distorted image are presented to the test subjects, and they are asked to indicate which image they prefer. The experimental results indicate that the C₁ channel is severely attenuated in the deuteranomalous trichromat test subjects, and that nearly all their color sensation is mediated by the C₂ channel of the color vision model     

彩色图像非参数变换立体匹配研究

将非参数Rank变换引用到彩色图像的立体配算法中,采用绝对值指数方法来计算像素的颜色相似性,对彩色图像进行一种分等级的改进Rank变换,将彩色图像转变了一个整数矩阵,然后建立一种新的匹配测度,同时加入色差梯度约束进行匹配。通过对比实验,表明这种新的匹配基元进行匹配,与直接采用灰度特征作为匹配基元的算法相比,有更好的抗噪性和匹配准确性。     

Analysis of color volume of multi‐chromatic displays using gamut rings

There are claims that multi‐chromatic displays can achieve a wider color gamut by the use of additional highly saturated secondary color channels. However, there are other claims that these displays lose lightness and/or color saturation at brighter levels. These apparently divergent views have led to some controversy in the display industry and at standard setting organizations. This study examines the color gamut volume for a variety of simulated and measured multi‐chromatic (sometimes incorrectly referred to as “multi‐primary”) displays using combinations of white and/or secondary color channels, such as cyan, magenta, and yellow. Furthermore, a two‐dimensional gamut representation, referred to as “gamut rings,” is introduced to illustrate that the addition of nonprimary optical color channels to a trichromatic (RGB) display can result in a significant decrease in the chroma at higher lightness levels. The additional saturated color channels can increase the gamut volume only around their hues at darker levels. The results also confirm the validity of comparing the color light output and white light output for revealing the design trade‐offs between the high‐peak white and the color‐image brightness for multi‐chromatic displays.     

A qualitative and quantitative study of color emotion using valence-arousal

This paper describes qualitative and quantitative analysis of color emotion dimension expression using a standard device-independent colorimetric system. To collect color emotion data, 20 subjects are required to report their emotion responses, using a valence-arousal emotion model, to 52 color samples that are chosen from CIELAB Lch color spaces. Qualitative analysis, including analysis of variance (ANOVA), Pearson’s correlation and Spearman’s rank correlation, shows that significant differences exist between responses to achromatic and chromatic stimuli, but there are no significant differences between chromatic samples. There is a positive linear relationship between lightness/chroma and valence-arousal dimensions. Subsequently, several classic predictors are used to quantitatively predict emotion induced by color attributes. Furthermore, several explicit color emotion models are developed by using multiple linear regression with stepwise and pace regression. Experimental results show that chroma and lightness have stronger effects on emotions than hue, which is consistent with our qualitative results and other psychological studies. Arousal has greater predictive value than valence.     

多摄像机图像拼接自动色彩均衡算法

针对多摄像机视频图像,分析了图像拼接技术中存在的问题,讨论了目前图像处理中常用的图像色彩均衡算法,提出了一种基于图像像素均值统计的亮度和色彩均衡处理算法。首先提取相邻两摄像机同步帧图像的重叠区域并对重叠区图像进行通道分离（RGB）,把其中一幅作为参考图像,另一幅作为目标图像,分别统计两幅图像各颜色通道像素均值差,用差值强制修正整幅目标图像。然后对修正后的图像和参考图像（整幅图像）进行颜色空间转换（RGB到HSV）,再次统计两幅图像亮度通道（V通道）均值差,用差值强制修正整幅目标图像亮度。实验结果证明,该算法能有效校正相邻摄像机图像的亮度和色差,对后期的拼接融合处理起到了很好的改善效果。     

基于色彩向量模型的彩色图象编码算法

在彩色图像编码技术中, 普遍存在的一个问题就是未能充分利用个色彩分量间的相关性。本文提出了一种基于色彩向量模型的彩色图象压缩编码算法, 高效地去除了彩色图像各分量间的相关性。该算法是将彩色图像 3 个色彩分量中一个分量, 将该色彩分量分割成若干个大小相等, 但不重叠的子块; 然后构造出该色彩分量的每个子块与另两个色彩分量所对应的子块中的色彩向量; 这样对另两个色彩分量的压缩编码转化为对色彩向量的编码。解码则是通过简单的逆变换, 以得到重构的两个色彩分量。这样一幅彩色图像就可以用一个色彩分量和其子块分割并计算出表示其它两个色彩分量的色彩向量来表示。实验结果标明, 该算法易于实现, 具有较高的峰值噪比和压缩比, 且恢复图像也具有视觉无损的效果。     

Computerized feature quantification of sublingual veins from color sublingual images

Characteristics of tongue pose the most important information for Traditional Chinese Medicine diagnosis. So far, extensive studies have been made on extracting tongue surface features, but rarely refer to sublingual vein that is also diagnostically important. This paper focuses on establishing a feature quantification framework for the inspection of sublingual veins, composed of two parts: the segmentation of sublingual veins and the feature quantification of them. Pixel-based sublingual vein segmentation algorithm and adaptive sublingual vein segmentation algorithm for color sublingual images with visible contrast and low contrast are proposed respectively. The experiments prove that the proposed algorithms perform well on the segmentation of sublingual veins from color sublingual images with both visible contrast and low contrast. A chromatic system in conformity with diagnostic standard of tongue diagnosis is established to characterize the chromatic feature of sublingual veins. Experimental results reveal that the breadth and chromatic features quantified by the proposed framework are properly consistent with the diagnostic standard summarized by tongue diagnosis.     

Seasonal variations in the color statistics of natural images

We examined how the distribution of colors in natural images varies as the seasons change. Images of natural outdoor scenes were acquired at locations in the Western Ghats, India, during monsoon and winter seasons and in the Sierra Nevada, USA, from spring to fall. The images were recorded with an RGB digital camera calibrated to yield estimates of the L, M, and S cone excitations and chromatic and luminance contrasts at each pixel. These were compared across time and location and were analyzed separately for regions of earth and sky. Seasonal climate changes alter both the average color in scenes and how the colors are distributed around the average. Arid periods are marked by a mean shift toward the +L pole of the L vs. M chromatic axis and a rotation in the color distributions away from the S vs. LM chromatic axis and toward an axis of bluish-yellowish variation, both primarily due to changes in vegetation. The form of the change was similar at the two locations suggesting that the color statistics of natural images undergo a characteristic pattern of temporal variation. We consider the implications of these changes for models of both visual sensitivity and color appearance.     

Color‐tuning projection system for adaptive combination of high brightness and wide color gamut

Abstract— The demand for projectors with high brightness and wide color gamut has been increasing; however, UHP lamp projectors cannot deliver those two qualities efficiently and simultaneously because of its color‐separation system. The newly developed projection system — “Color‐Tuning Projection System” — realizes the adaptive combination of high brightness and wide color gamut with one projector. This projector features a fourth liquid‐crystal panel — “Color Tuner” — with a 3LCD optical engine, which controls yellow light separately from the RGB light of a UHP lamp. This color‐tuner‐based optical engine — “Color‐Tuning Optical Engine” — and a new color‐conversion signal‐processing algorithm — “Adaptive Color Conversion Algorithm” — controls the yellow‐light volume and corrects color‐shifted pixels according to the brightness and chromaticity analysis of the input image, key technologies of the Color‐Tuning Projection System. This additional panel system enables the projector to ach ieve up to 115% higher brightness and 120% wider color gamut according to the input image. This paper presents an innovative design concept, a novel technology regarding brightness and a color‐gamut conversion projection system, and the characteristics of the prototype.     

Mach band optical ray illusion—Drawing with the second differential

Mach bands running along convex ramp edges in a computer graphics image produce the illusion of optical rays, and a concave ramp edge defines an interface for “reflection.” The positive and negative brightness enhancements (E) observed in the illusion are simulated by convolving the pattern of gradient increments (Δg) computed at the edges with a Gaussian kernel (G): E ∝ − Δg G.     

Screen‐based color vision test for digital quantification of deutan color defects using a color‐calibrated monitor

Display technologies are used in various industries. However, few studies on color vision testing using self‐luminous displays are reported. In this study, a screen‐based color vision test, termed the digital color vision test (DCVT), is developed on a color‐calibrated monitor. A control bar is adjusted by the observer to build just noticeable chromatic difference ellipses in CIE u′v′ chromaticity diagram, which indicate the capabilities of subjects' color visions. Ten color‐normal observers and 13 deutan observers participated in the psychophysical experiments. The observers also performed the other two typical diagnostic tests (D‐15 and anomaloscope). Results from the experiment using the adjustment psychophysical method for digital quantification of deutan color vision defects are presented. It is found that the diagnosis accuracy of the DCVT is approximately equivalent to those of D‐15 and anomaloscope tests.     

Modeling human color categorization

A unique color space segmentation method is introduced. It is founded on features of human cognition, where 11 color categories are used in processing color. In two experiments, human subjects were asked to categorize color stimuli into these 11 color categories, which resulted in markers for a Color LookUp Table (CLUT). These CLUT markers are projected on two 2D projections of the HSI color space. By applying the newly developed Fast Exact Euclidean Distance (FEED) transform on the projections, a complete and efficient segmentation of color space is achieved. With that, a human-based color space segmentation is generated, which is invariant for intensity changes. Moreover, the efficiency of the procedure facilitates the generation of adaptable, application-centered, color quantization schemes. It is shown to work excellently for color analysis, texture analysis, and for Color-Based Image Retrieval purposes.     

Applying the AHP approach to evaluate human sensitivity to chromatic light

The difference threshold of judging chromatic light was evaluated in this study. The experimental factors included target colour, background colour, interspacing, target surface interferences, and luminance level. Results showed that humans were more sensitive to green light than to red or blue light. The differential brightness sensitivity was higher for dark target on bright background than for bright target on dark background. The interspacing between two targets also affected differential brightness sensitivity, but the luminance level of the standard stimulus was found to have no effect on difference threshold. In addition, there was significant individual differences in differential brightness sensitivity. Further, by comparing the results obtained from the Analytic Hierarchy Process (AHP) and the method of constant stimuli, it suggests that the AHP approach was a valid and effective method to assess difference threshold.     

一种颜色保持的彩色图像增强新算法

分析了Retinex理论及其典型彩色图像增强算法,在此基础上提出一种颜色保持的彩色图像增强新算法。利用非线性sigmoid传输函数多尺度增强亮度分量,并进行局部对比度增强后获得亮度增益曲面,最后利用亮度增益曲面对原彩色图像RGB三颜色分量同比增强,保证了色调恒定不失真。几种算法实验结果的比较和分析。表明,这种算法是有效的。     

Applying the AHP approach to evaluate human sensitivity to chromatic light

The difference threshold of judging chromatic light was evaluated in this study. The experimental factors included target colour, background colour, interspacing, target surface interferences, and luminance level. Results showed that humans were more sensitive to green light than to red or blue light. The differential brightness sensitivity was higher for dark target on bright background than for bright target on dark background. The interspacing between two targets also affected differential brightness sensitivity, but the luminance level of the standard stimulus was found to have no effect on difference threshold. In addition, there was significant individual differences in differential brightness sensitivity. Further, by comparing the results obtained from the Analytic Hierarchy Process (AHP) and the method of constant stimuli, it suggests that the AHP approach was a valid and effective method to assess difference threshold.     

基于模糊理论的低照度彩色图像增强算法

低照度彩色图像存在整体亮度低、对比度差、颜色偏暗和信噪比低等特点,传统图像增强算法对其增强效果非常有限。提出了一种基于模糊理论的低照度彩色图像增强算法,将三原色(red,green,blue,RGB)图像转换成色相饱和度(HSV)图像,以保证增强处理不引起图像的色彩失真。对亮度图像进行非线性变化,实现动态范围展宽;采用修正后的隶属度函数将图像映射到模糊平面,实现对比度增强。实验结果表明:该算法显著地提高了图像整体亮度和对比度,改善了低照度彩色图像的视觉效果。     

基于多维特征向量及ANN技术的色彩传递算法

灰度图像色彩传递可以实现对灰度图像的自动上色处理。分析了目前色彩传递的经典算法——Welsh算法,指出了该算法存在的两大不足之处,提出了一种包含高频纹理信息的向量式像素点描述方式,并结合最近邻域搜索算法（ANN）,提出了一种新的色彩传递算法,弥补了传统算法的不足,使灰度图像的彩色化效果有了较大改进。     

Wide color gamut and high dynamic range displays using RGBW LCDs

An increasing number of studies on efficient implementation of vivid and realistic displays are being conducted as liquid crystal displays (LCDs) become widely used in TV applications. For vivid displays, the specifications such as wide color gamut (WCG) and high dynamic range (HDR) should be implemented in LCDs. However, the low transmittance rate of the WCG and the significant costs for the peak luminance capability of the HDR are major obstacles. Hence, an RGBW LCD, which is capable of increasing the transmission efficiency, may be a good platform to overcome these problems.In this paper, we estimate the perceived brightness effect of the WCG by using the Helmholtz–Kohlrausch (H–K) effect on RGB and RGBW LCDs. The simulation results showed that the RGBW LCD was more suitable for adopting the WCG than the RGB LCD in terms of the brightness balance of achromatic and chromatic colors, and the results were also confirmed by subjective tests. In addition, we propose an effective method to implement the HDR display based on the RGBW LCD. The data stretch, considering a local adaptation characteristic of a human visual system (HVS), greatly enhanced the details of the dark regions, and the local peak dimming using the white channel analysis and the white channel data itself increased the expressiveness of the peak luminance in irradiative or specular regions to 1500 nits.     

Fusion of color edge detection and color quantization for color image watermarking using principal axes analysis

In the past few years, many gray-level image watermarking schemes have been proposed, although the extension to the color case is rare and regularly accomplished by marking the image luminance, or by processing each color channel separately. This paper presents a new color image watermarking scheme that combines color edge detection and color quantization using principal axes analysis in three-dimensional color space. The watermark is hidden within the data by modifying a subset of carefully selected edge points to resist both geometric distortion and signal processing attacks. Experimental results show the robustness of the proposed scheme to resist common attacks.