Measurement of Color Constancy by Color Memory Matching

Degree of color constancy was measured when color memory was involved in color comparison judgment. We used the Optical Society of America (OSA) Uniform Color Scales as stimulus color samples, and chose 20 color samples as test stimuli. Four illuminants of 1700, 3000, 6500, and 30, 000 K were tested. The observer, completely adapted to a test illuminant, saw a test color sample and stored its color in his memory. After being readapted to the reference white (6500 K), he started selecting a color sample from among the 424 OSA samples which matched the test sample in his memory. We employed a memory matching method called cascade color matching, in which the number of selected color-samples was gradually reduced in four stages. In the final stage, the observer selected a color sample. The results show that, for most test colors, the distributions of selected colors in stages 1 to 4 were similar among all illuminants, and that the u’v’ chromaticity distance between a test color under 6500 K and its matched color was quite short. These indicate that good color constancy was retained in memory color comparison.     

Dynamics of Asymmetric Color Matching

It is known that the human color constancy is not complete. We conducted asymmetric color matching experiments to clarify a simple question: what was it that the observer matched. Observers made apparent-color matches between Munsell color chips under D₆₅ illumination and a color chip presented on a CRT. The observers’ matches showed incomplete color constancy. We applied relative cone-weight transformation to each observer’s results under control condition, so as to equate the unique-white point for each illuminant condition. The result of this simple transformation showed good match to the actual data. Our results suggest what the observer was doing during the asymmetric color matches was picking up apparent-color signal, achieved from the test color chip under D₆₅, and reconstructing it with respect to the unique-white by a simple cone response scaling.     

Change of Color Appearance in Photopic,Mesopic and Scotopic Vision

Mesopic vision describes a range of light levels where vision is mediated by both cones and rods. The appearance of color in mesopic vision differs drastically from that in photopic vision, where only cones mediate visual information. We used a haploscopic color matching technique to investigate the color appearance under various illuminance levels, ranging from photopic to scotopic via mesopic levels. The observers did color matching between a test color chip under various illuminance levels and a matching color stimulus presented on the Cathode-Ray Tube (CRT) display under the photopic illuminance condition. The results showed that not only chroma and lightness but hue of most color chips changed with illuminance. The manner of the hue changed depended on the color of the test chip, while matching points approached a neutral gray with decrease in illuminance level for all test chips. Chroma reduced continuously with decrease of the illuminance level until 0.1 lx for reddish and yellowish color chips or until 1 lx for greenish and bluish ones. Beyond those illuminance levels, chroma was approximately constant. Lightness decreased with decreasing illuminance level for all test chips except bluish color chips, for which lightness did not decrease much in general and even increased in some cases as predicted by the Purkinje shift. The experimental results obtained in the present study provide critical features that should be considered in predicting the appearance of color at low light levels.     

Color Discrimination Characteristics Depending on the Background Color in the (<Emphasis Type="Italic">L</Emphasis>, <Emphasis Type="Italic">M</Emphasis>) Plane of a Cone Space

We investigated color discriminability on the background color. The measurement was carried out at over 21 background colors in (L, M) plane of a cone space by four observers. We used low temporal stimulus frequency (1 Hz) so that threshold was determined by the red-green opponent mechanism. Results showed that color discriminability depends on the background colors. Threshold was higher with a more saturated background color. This suggests that the sensitivity of the red-green opponent mechanism is high when the mechanism’s output is small and increases with the output levels of the mechanism. To confirm this relationship between the red-green mechanism and color discriminability, color appearance depending the background color was also evaluated. There was a strong correlation between the sensitivity and the perceived whiteness. Both sensitivity and whiteness value were highest at around the equal energy white point and decreased with increase in the difference between background color and equal energy white. This suggests that the adaptation state of the red-green opponent color controls color discrimination.     

Strategy correlations and timing of adaptation in Minority Games

We study the role of strategy correlations and timing of adaptation for the dynamics of Minority Games, both simulationally and analytically. Using the exact generating functional approach à la De Dominicis we compute the phase diagram and the behaviour of batch and on-line games with correlated strategies, complementing exisiting replica studies of their statics. It is shown that the timing of adaptation can be relevant; while conventional games with uncorrelated strategies are nearly insensitive to the choice of on-line versus batch learning, we find qualitative differences when anti-correlations are present in the strategy assignments. The available standard approximations for the volatility in terms of persistent order parameters in the stationary ergodic states become unreliable in batch games under such circumstances. We then comment on the role of oscillations and the relation to the breakdown of ergodicity. Finally, it is discussed how the generating functional formalism can be used to study mixed populations of so-called ‘producers’ and ‘speculators’ in the context of the batch Minority Games.     

Finite-Temperature Field Theory on the Light Front

The formulation of statistical physics using light-front quantization, instead of conventional equal-time boundary conditions, has important advantages for describing relativistic statistical systems, such as heavy ion collisions. We develop light-front field theory at finite temperature and density with special attention to quantum chromodynamics. First, we construct the most general form of the statistical operator allowed by the Poincaré algebra. In light-front quantization, the Green’s functions of a quark in a medium can be defined in terms of just two-component spinors and do not lead to doublers in the transverse directions. Since the theory is non-local along the light cone, we use causality arguments to construct a solution to the related zero-mode problem. A seminal property of light-front Green’s functions is that they are related to parton densities in coordinate space. Namely, the diagonal and off-diagonal parton distributions measured in hard scattering experiments can be interpreted as light-front density matrices.     

Construction of a two- dimensional colour hologram using a source encoding technique

An adaptation of the source-encoded image subtraction system is used to form an in-plane holographic image of a colour transparency. The colour image can be retrieved by simple spatial filtering with a white-light optical processor.     

Red in Estonian popular belief and folk costume

A visit by one of the authors to Estonia, and the discovery that the term ‘red’ was used locally for the colour ‘orange’, led to a detailed study of the colour red in Estonian belief and culture. The study is reported here, together with an interpretation of the red/orange substitution based on Berlin and Kay's model of colour term development in language.     

Investigation of unique hue setting changes with ageing

Clromatic sensitivity along the protan, deutan, and tritan lines and the loci of the unique hues (red, green, yellow, blue) for a very large sample (n = 185) of colour-normal observers ranging from 18 to 75 years of age are assessed. Visual judgments are obtained under normal viewing conditions using colour patches on self-luminous display under controlled adaptation conditions. Trivector discrimination thresholds show an increase as a function of age along the protan, deutan, and tritan axes, with the largest increase present along the tritan line, less pronounced shifts in unique hue settings are also observed. Based on the chromatic (protan, deutan, tritan) thresholds and using scaled cone signals, we predict the unique hue changes with ageing. A dependency on age for unique red and unique yellow for predicted hue angle is found. We conclude that the chromatic sensitivity deteriorates significantly with age, whereas the appearance of unique hues is much less affected, remaining almost constant despite the known changes in the ocular media.     

The influence of ambient illumination on colour adaptation in three fringe photoelasticity

In three fringe photoelasticity, a single colour isochromatic image is used to estimate the total fringe order by comparing the colour at each point with that of a calibration table. The generation of the calibration table is critical, and certain nuances involved therein are brought out in this paper. Ideally, the same specimen material and lighting conditions must be used for both the calibration and application experiments, which are often not possible in an industrial scenario, and colour adaptation is a simple way of suitably modifying the calibration table. Till date, only experimental analyses of the colour adaptation procedures are available in the literature; in this paper, the colour adaptation procedures are investigated from an analytical viewpoint. This study has brought out that a two-point colour adaptation scheme accounts not only for tint variation between the calibration and application specimens, but also for ambient illumination. This finding has also been experimentally verified for a benchmark problem, and thereafter extended for reflection photoelastic analyses.     

High-p jets in diffractive electroproduction

The diffractive production of high-p jets in deep-inelastic scattering is studied in the semiclassical approach. The p-spectra of and diffractive final states are found to be qualitatively different. For fina states, which are produced by ‘hard’ colour-singlet exchange, the p-spectrum is much softer than for final states, where the colour neutralization is ‘soft’. Furthermore, the two different final states can be clearly distinguished by their diffractive mass distributions.     

浅谈色觉的数学机制

正常人眼拥有色觉功能,其目的是为了辨识不同的光辐射能谱分布。色觉的生理基础是:在视网膜上具有三类视锥细胞,它们将光信号转换成为使大脑便于分析和处理的神经电信号。由于单个视锥细胞产生的神经电信号只反映光辐射的强度信息,所以光辐射的谱信息(波长分布)须由三类视锥细胞的响应比来反映。以光辐射中的单色辐射及线性连续辐射为辨识对象,构造了光辐射辨识的数学模型。基于该模型,对用三类视锥细胞的响应比来表征光辐射的谱信息这一命题的必要性与完备性进行了理论论证。     

Chromatic Spatial Summation at Equiluminance

The effect of spatial summation on chromatic detection at suprathreshold levels for the red-green and yellow-blue chromatic opponent mechanisms has been studied using simple reaction time (RT) as a measurement of the response. We varied the target size in the experiments from 8 min of arc in diameter to 10 deg, and the hue-substitution paradigm was adopted to generate only chromatic changes in the cone input. Equiluminant stimuli were distributed along three tritan and three red-green confusion lines. Three reference stimuli were chosen as both reference and adapting stimuli, in this case to determine whether the chromatic adaptation affected the spatial summation. The results showed that the mean value of RT at a constant cone-input variation, either of the L #x2212; 2M channel or of the S #x2212; (L #x002B; M) channel, against the target size decreased until a stimulus size was reached, the RT being constant for greater sizes. The spatial summation was fulfilled for a maximum target size which was less for the L #x2212; 2M channel than for the S #x2212; (L #x002B; M) channel, this size decreasing as the cone-input variation rose. Furthermore, there was no spatial summation for high-enough variations in the cone input. In addition, the chromatic mechanisms appear to organize their spatial integration with the adapting level.     

Practical colour management

Spectrophotometers have been successfully used for colour measurement. This paper addresses digital imaging as a complementary and alternative method of colour measurement and appearance and an effective communication tool as part of a practical colour management programme within the supply chain of a textile retailer. The specific needs—to measure and communicate textured dyed material and printed fabric—are discussed, as well as the colour specification and quality control (QC) of currently un-measurable fabrics and accessories. A unique method of using digital imaging for the assessment of colour fastness will also be discussed.     

Colour and lighting in hospital design

Little information or guidance has been available to assist the development of a hospital's visual environment. A report on lighting and colour design schemes, accessible to non professionals with responsibility for refurbishment strategies, was required by NHS Estates. Firstly, 20 hospitals were audited to establish a picture of current practice and to identify key issues where colour design could broadly enhance the environment for patients, staff and visitors. Critical areas were outlined in this report, where colour design can be utilised and applied, for the benefit of all users, from ambience to essential legal requirements such as colour contrast for the visually impaired.Provision of staff relaxation rooms that are different in terms of colour and lux levels from immediate work spaces, or thoughtfully designed areas for patients awaiting intensive treatment, have been shown to have some beneficial effects on a sense of well being. Colour and design have not been established as a definite cure for sickness and ill health, but certainly monotony and poor conditions in premises that have not been refurbished with any care, have had a detrimental affect on recovery rates and staff morale. The realisation that a well balanced and attractive environment is of major importance to patients’ health is, in no way new; Florence Nightingale observed that ‘a variety of form and brilliance of colour in the objects presented to patients are an actual means of recovery’.     

颜色温度和相关色温的不确定度评定方法

颜色温度和相关色温是光源的重要参量。从色品坐标(u,v)到颜色温度和相关色温的计算过程比较复杂,很难依据国际标准化组织推荐的不确定度评定方法进行分析。介绍了从光谱辐射功率和色品坐标(u,v)的不确定度出发,按照国际标准化组织的推荐方法,得到更为科学合理的颜色温度和相关色温的不确定度评定方法。针对新的国家颜色温度副基准,分别采用基于数学模型的精确方法、近似方法和几何方法对其不确定度进行了评价,并与传统方法进行了比较。采用传统方法得到的计算结果偏高,这是因为传统的计算方法很大程度上基于实验和经验估计,没有将颜色温度的不确定度与光谱辐射功率和色品坐标(u,v)的不确定度之间建立明确的数学关联,在分析过程中存在对某一不确定度源进行重复计算的可能。所述的数学推导方法相对传统方法更为科学合理。     

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。     

Principal component and sampling analysis of color spectra

We studied the effect and relation between the optimal sampling interval and the optimal number of principal component analysis eigenvectors for color spectra. The effect of different type of light sources and illuminants are included in the study. Several reflectance spectra sets under different real light sources and standard illuminants were used as a test set. The needed sampling interval and number eigenvectors with different light sources and illuminants are found. The used bandwidth in measurements causes effect to the resulted optimal sampling interval, which is also shown.     

A Color Appearance Model Applicable in Mesopic Vision

We propose a color vision model that can be used to predict color appearance in mesopic vision as well as photopic and scotopic vision. It is based on a two-stage model which consists of the cone and opponent stages and it assumes rod intrusion at the opponent stage. The model has the following features to describe the color appearance in mesopic vision. First, it includes a gradual and nonlinear shift in spectral luminous efficiency from V (LD) to V (LD) to cope with the spectral sensitivity difference between photopic and scotopic vision and the nonlinearity of rod influence on the luminance channel. Second, the model assumes decrease of the chromatic component with decreasing illuminance to explain the reduction of saturation at low illuminance levels. Third, it assumes that red/green and yellow/blue components change with illuminance levels independently, thus explaining hue shifts with decreasing illuminance. We applied the model for color appearance simulation of natural scenes in a mesopic visual environment.     

Non-renormalization of the weak vertex in gauge theories with integrally charged quarks

We give current algebra arguments to show that toO(α) the colour octet vertices do not renormalize the effective weak vertex between colour singlet hadrons in models with broken colour symmetry. The result does not depend on the details of the mixing between colour gluons and electro-weak bosons.