CIELAB与CIECAM02色空间均匀性比较研究

采用均匀色空间Munsell系统检验和验证了CIELAB和色貌模型CIECAM02色空间的均匀性。利用Mun- sell色卡所对应的三刺激值X,Y,Z作为模型的输入值,预测色空间模型的明度、彩度和色调,并通过预测结果比较和检验了CIELAB色空间和CIECAM02模型色空间的均匀性。研究表明:在预测明度方面,两个色空间的结果相似;在预测彩度时,CIECAM02模型较好于CIELAB色空间;在预测色调时,当色调逐渐从BG变化到B时,CIELAB所预测的色调角与由Munsell色空间计算出来的色调角之差逐渐增大,最大时超过6%,而CIECAM02所预测的色调角与Munsell色空间的色调角之差在2.5%以内,CIECAM02优于CIELAB色空间。     

Color appearance and visual measurements for color samples with gloss effect

We assess the color appearance of the samples with different inks on glossy substrates, five kinds of paper with different gloss levels. The color samples are measured using spectrophotometers under different illuminating/viewing geometries and visually estimated using the psychophysical method of magnitude estimation. The results of the two approaches are compared through the color appearance model of CIECAM02. The experimental data analysis indicates that the 0/45 and 15/0 geometries can be used to describe the two major aspects of gloss effect, the enlargement of color gamut, and the reduction of lightness. The agreement for hue attribute between instrumental measurement and visual assessment is better than those for colorfulness and lightness.     

不同环境参数下CIECAM02的跨媒体颜色复现性能

为研究CIECAM02三种环境参数(dark,dim,average)在三种相应照明环境下的跨媒体颜色复现性能,基于记忆匹配和成对比较的心理物理学实验方法,在灯箱照明打印样本与Dark,Dim,Average三种不同环境照明条件下液晶显示器显示色样之间进行了跨媒体颜色复现实验。实验数据分析表明,采用dim环境参数在三种照明条件下都能达到较优的颜色复现性能,而dark和average参数性能与测试颜色的明度和彩度存在一定相关性,较暗色样在Dark条件下采用dark参数设置复现良好,但在Average实验条件下采用average参数设置时性能很差;对于较亮色样的复现,dark与average参数设置在其相应实验条件下的颜色复现性能无显著差异。     

Lightness constancy:from haze illusion to haze removal

The human visual system processes lightness constancy to estimate reflectance under complex viewing conditions. We focus on the underlying reason the human visual system is conscious of haze, and discuss the single-image haze-removal problem based on lightness constancy from the beginning of haze illusion. Following the basic principle and model of "atmospheric transfer function", we bring about a simple dehazing paradigm by estimating two values using bilateral filtering. Practical investigation of parameters and design are analyzed in detail. Furthermore, a novel quantitative standard haziness presents itself naturally during the estimation process. Comparative study and objective evaluation demonstrate that the proposed method is fast and effective, yielding high-contrast and vivid haze-free images.     

可见光与红外彩色融合图像感知清晰度评价模型

提出了感知清晰度评价模型,来评价人眼对红外与可见光彩色融合图像细节和边缘的可辨识度。首先,利用人眼对比度敏感函数模型,抑制在特定观察条件下图像中人眼不敏感的频率成分。之后,在局部频带对比度模型基础上,结合人眼亮度掩模特性构造了感知对比度模型。最后,计算融合图像人眼兴趣区域(细节和边缘区域)的感知对比度,进而评价融合图像的感知清晰度。实验结果表明,与现有的五种彩色图像清晰(模糊)度的客观评价模型相比,考虑人眼视觉特性感知清晰度模型的计算结果与人眼主观感受具有较好的一致性,可以有效地对彩色融合图像清晰度进行客观评价。     

Evaluation of small suprathreshold color differences under different background colors

A psychophysical experiment under constant stimuli is conducted on a CRT display to measure the visual suprathreshold color differences for five color centers recommended by CIE under the same five background colors.The performances of four CIELAB-based,three CIECAM02-based,and two OSA-UCS-based formulas are tested.Detailed analysis results indicate the existence of chromatic crispening effect.CIEDE2000 performs best for the gray center and gray background,whereas CAM02-LCD and CAM02-UCS have the best performance for non-neutral backgrounds.CAM02-LCD significantly outperforms all other formulas for all color centers under all background colors.     

CIECAM02-UCS based evaluation of colorimetric characterization modeling for a liquid crystal display using a digital still camera

A method for characterizing a liquid crystal display (LCD) was developed using a characterized digital still camera (DSC). Prediction accuracy of the method was evaluated through calculating the Euclidean distance between prediction and the corresponding reference in the most lately standardized color appearance model CIECAM02 with rescaled lightness. This paper describes a framework for obtaining a device-independent representation of displayed colors on the monitor with a less time-consuming method for accurate characterization. A DSC was first characterized using a polynomial model and then an LCD was characterized using two instruments: a tele-spectroradiometer and the characterized DSC. In total, five characterization methods were tested of which PLCC predicted the results most accurately.     

Prediction of Chinese color system appearance scales using various color appearance models

The chromaticities of the Chinese color system dataset are applied to eight color appearance models (CAMs). Models used are: CIELAB, Hunt, Nayatani, RLAB, LLAB, ZLAB, CIECAM97s, CIECAM02.     

色貌模型的人工神经网络方法的研究

色貌模型(CAM)主要解决不同观察条件、不同背景和不同环境下的颜色真实再现问题。采用人工神经网络(ANN)的方法来实现目前最新的色貌模型CIECAM02的预测,包括正向预测(从色度参数到色貌属性参数)和逆向预测(从色貌属性参数到色度参数),应用自然色系统(NCS)中的部分色样作为神经网络的训练和测试样本。由于正向输出色貌属性参数空间不是均匀的,对于网络预测精度用特殊方法评估,而对于逆向模型则可直接利用LAB色差公式评价。测试的结果表明:用神经网络对CIECAM02模型的预测达到了较高的精度。     

Phenomena of Apparent Lightness Interpreted by the Recognized Visual Space of Illumination

Many experimental results have been reported which demonstrated deviation of the apparent lightness from the calculated lightness based on spectral reflectance, and these have caused debate among researchers as to the models to explain them. The judgement of lightness of objects that we see in the outside world is one of the most important tasks in our daily life. We proposed the recognized visual space of illumination, RVSI, as a three dimensional recognition constructed in the brain for the outside world, and showed that the apparent lightness was determined in relation to the size of the RVSI. In the present paper the concept was applied to various results of lightness experiments such as the White effect and simultaneous contrast, and based on the proposition that an observer first builds a three dimensional RVSI from a two dimensional pattern and the lightness of a test patch was judged in relation to the size of this RVSI, the results were then globally and nicely explained. A new demonstration of a pattern was proposed to give different apparent lightness for patches with the same physical lightness to strengthen the proposition. The importance of distinguishing between a test patch and a surrounding field was emphasized when one does a lightness experiment and interprets the results.     

Monocular viewing prolongs reversal interval of perceptual rival figure

The authors examined whether the perceptual reversal rate changes under monocular versus binocular viewing conditions. Our results suggest that the perceptual reversal interval increases during monocular viewing. The ratio of the reversal rate (1/interval) for the two viewing conditions (binocular/monocular) was 1.28 over a wide range of pattern luminance levels. The quoted ratio was 1.40 when the luminance was high. Such a ratio parallels the value of a well-known binocular summation index $(\sqrt 2 )$ , which was derived from the signal detection theory. The binocular summation index shows that the strength of an input signal is enhanced by binocular viewing. However, how the binocular summation shortens the perceptual reversal interval is unclear. This issue can be resolved if the perceptual reversal is derived by integrating the strength of an unconscious image signal. Thus, we discussed the mechanism of perceptual switch by associating two classical, well-studied phenomena, binocular summation and perceptual switch.     

照明光源及纸张色彩对传统书法作品展陈喜好的影响

书法是中国传统文化独有的文字艺术表现形式。书法作品的展陈喜好,其实质为色彩组合喜好中的色彩图形喜好问题。本研究针对现阶段书法作品展陈方式在颜色科学层面缺乏合理依据的问题,以主客观实验为基础,就照明光源及纸张色彩对传统书法展陈喜好的影响进行了分析与讨论。研究首先通过相关色温2 500, 3 500, 4 500, 5 500和6 500 K共五种典型LED照明光源相对光谱功率分布以及白色、黄白、浅白、红色、橙色共五种典型书法纸张光谱反射率信息的测量,获取光源及纸张色彩原始信息,并分别将其转换至CIEXYZ以及CIECAM02颜色空间。随后,将光源及纸张色彩属性与基于40名观察者心理物理学实验的1 000组书法展陈喜好数据进行关联性分析,进而从相关性分析、多元回归分析以及正态分布分析等多个统计学角度对传统书法作品展陈喜好的影响因素进行讨论。实验结果显示,传统书法作品展陈照明喜好与普通场景色彩喜好相比具有显著的特殊性,其喜好程度与明度对比、色相对比等色彩属性相关性较低,而主要受光源因素的影响。本研究的开展,将为当前传统书法作品的展陈照明工作提供有效的理论与方法参考,对于当前博物馆及美术馆的光源设计工作具有一定的指导意义。     

颜色视觉匹配中明度阈值的评价

为了对颜色视觉匹配中的明度阈值特性进行评价,采用在阴极射线管显示器上获得的颜色刺激,在5个不同明度的中性色背景下,标准刺激的明度L*从5到95以5个CIELAB单位为变化步长,共对19个不同明度的中性标准颜色进行视觉匹配实验。通过对实验结果的处理和分析,验证了关于颜色刺激视觉辨别明度阈值与背景明度之间相关性的韦伯法则和crispening效应,同时利用颜色视觉匹配数据对基于CIELAB的相关色差公式进行了评价和比较,CIEDE2000具有最好的明度差预测性能,CMC次之,CIELAB和CIE94最差。     

Improvement in appearance of colors for elderly persons using lightness transform

The color of an object appears to be different for elderly and young persons. This is because human visual features vary with on age. In general, the spectral transmittance of the crystalline lens of an elderly person is lower than that of a young person. The low spectral transmittance decreases the brightness of the visual field. This phenomenon affects the color appearance of an image in human visual perception. In this paper, a lightness transform method is proposed to improve the color appearance of images for elderly persons. In the proposed method, colors that are difficult for an elderly person to see are transformed into colors that are easy to see by adding lightness contrast. The performance of the proposed method is confirmed in experiments using digital images.     

Using a time-delay and integration camera at a non-zero viewing angle under vibration conditions

The use of a TDI camera is restricted to cases of viewing from the direction of the surface normal. Our previous work indicated that a TDI camera can be used with viewing angles up to 30° from the surface normal which extends the usability of TDI for visual inspection applications. The objective of this paper is to examine the use of a TDI camera at a non-zero viewing angle under vibration conditions. The effects caused by vibration of the surface to be viewed become critical when using a TDI camera at non-zero viewing angles. A method of approximating the TDI performance under vibration conditions was determined and evaluated experimentally. The resulting measurements support the approximating method developed here.     

Effect of Space Recognition on the Apparent Lightness of Gray Patches Demonstrated on Printed Patterns

The retinal image of the outside world is two dimensional and the brain automatically transfers the 2D image to 3D space in order that a human can recognize the world correctly. A printed black and white picture of a grating or a cube was presented to subjects through a viewing box to exclude other objects than the pattern so that the brain was provided with only the information about the pattern and recognized a 3D space for the pattern efficiently. Once a space recognition was achieved there was constructed a recognized visual space of illumination (RVSI) which controlled the apparent lightness of gray patches drawn in the picture. In the grating experiment the apparent lightness of a gray stimulus drawn as if it were located on this side of the white stripes, was shown to become lower than that of a gray reference stimulus drawn behind the white stripes with black background when both stimuli had the same lightness. Similarly, in the cube experiment the apparent lightness of a gray stimulus drawn way behind the white cube was shown to become lower than that of a gray reference stimulus drawn over black stripes that lay on the cube. The amount of these space recognition effects on apparent lightness was about 0.5 in Munsell Value when measured by brightness matching between the test and the reference stimulus.     

用不同光泽和色差等级的彩色印刷样品检验均匀颜色空间

用不同光泽纸张和不同色差等级彩色印刷样品的目视评价色差数据拟合色度椭圆,研究各均匀颜色空间在评价不同光泽度和色差样本时的表现,检验基于CIELAB,DIN99,OSA和CIECAM02共7个颜色空间的均匀性。用局部均匀性和全局均匀性因子分别检验不同颜色空间色度椭圆的椭圆度和空间中不同位置椭圆尺寸的一致性。结果表明,其他所有颜色空间的表现均优于CIELAB和OSA颜色空间,OSA-Gp-Eu和DIN99d颜色空间在评价印刷品颜色差异的表现上较为接近,同时优于其他的颜色空间。     

基于模式识别技术的色貌模型评价研究

选用Munsell新标数据集,采用基于模式识别技术的圆度、色相角偏差、明度线性度与空间投影点聚集度四个指标来分别评价目前八个典型色貌模型在彩度均匀性、色相预测准确性、明度均匀性、颜色的空间再现的能力。结果表明,不同的色貌模型在四个方面的颜色再现性上表现出不同的优势。八个色貌模型对彩度预测最好的是RLAB,每个色貌模型对红色和绿色预测比较好,CAM02在色相预测整体上占优势;明度的均匀性预测都比较好,尤其是CIELAB;LLAB的颜色的空间再现能力最好。     

Perceptual contrast enhancement with dynamic range adjustment

Recent years, although great efforts have been made to improve its performance, few Histogram equalization (HE) methods take human visual perception (HVP) into account explicitly. The human visual system (HVS) is more sensitive to edges than brightness. This paper proposes to take use of this nature intuitively and develops a perceptual contrast enhancement approach with dynamic range adjustment through histogram modification. The use of perceptual contrast connects the image enhancement problem with the HVS. To pre-condition the input image before the HE procedure is implemented, a perceptual contrast map (PCM) is constructed based on the modified Difference of Gaussian (DOG) algorithm. As a result, the contrast of the image is sharpened and high frequency noise is suppressed. A modified Clipped Histogram Equalization (CHE) is also developed which improves visual quality by automatically detecting the dynamic range of the image with improved perceptual contrast. Experimental results show that the new HE algorithm outperforms several state-of-the-art algorithms in improving perceptual contrast and enhancing details. In addition, the new algorithm is simple to implement, making it suitable for real-time applications.     

Approximating the CIECAM02 color appearance model by means of neural networks

An artificial neural network used to realize the approximating problem of the color appearance model (CAM) CIECAM02 in color management is demonstrated. GretagMacbeth ColorChecker Charts, which now are widely used in calibration of digital camera, are chosen as sanples to implement the forward and reverse color appearance models. When the predictive results are evaluated, for forward model, the output color appearance space is converted to the uniform color space based on CAM and is evaluated, while for reverse model, because the prediction precision is insufficient, we try to convert the color appearance space, which is the cylinder space, to the cube space similar to the red, green, and blue (RGB) space, and the results show that the precision is obviously improved.