NIST 0:45 reflectometer

The NIST 0:45 reflectometer measures the spectral reflectance factor at an influx angle of 0° and an efflux angle of 45° of colored, nonfluorescent specimens at room temperature, with widths ranging from 3 to 10 cm and heights from 3 to 20 cm and with an uncertainty of less than 0.5 in color difference units. Published in 2008 by John Wiley & Sons, Inc. Col Res Appl, 33, 94–99, 2008     

Uncertainty evaluation and propagation for spectral measurements

The measurement of the spectral power distribution (SPD) of a radiation source by array spectroradiometers is a technique that is widely used. In many applications, quantities that are derived from the SPD by a weighted integral over a wavelength interval are of interest. These integral quantities ought to be accompanied by a reliable uncertainty statement, for example, to assess conformity with prescribed limits or in order to judge the consistency of results obtained at different laboratories. We have developed a generally applicable Monte Carlo procedure for evaluating the uncertainty of spectral measurements. The procedure naturally accounts for correlations in the SPD which turn out to be crucial. Means are provided to handle and transfer these large‐scale correlation matrices easily. The proposed approach is illustrated by the determination of the SPD of colored LEDs from array spectroradiometer measurements, together with the derived CIE 1931 color coordinates. MATLAB^TM software implementing the proposed analysis procedure is made available.     

Transferring the 45/0 spectral reflectance factor scale

The accuracy of spectrophotometric measurements is limited by the standards that are used to calibrate the instrument. Therefore, the procedure used in transferring the spectral reflectance factor scale from one material to another for use in calibration must induce the minimum amount of error. the Munsell Color Science Laboratory has been transferring the spectral reflectance factor scale to calibration materials using a statistical method to correct for the most pervasive systematic errors in the measurement process. This method is based on a statistical procedure in which a set of systematic spectrophotometric errors are estimated based on the measurement of seven NIST primary standards and corrected in subsequent measurements. the optimization of the spectral reflectance factor scale to NIST standards minimizes the induced error. the average reflectance factor error consistently found between the corrected measurements of the NIST standards and their certificate values have been 0.0006 and the average δ_ab has been on the order of 0.2.     

Uncertainty estimation in colour measurement

A current concern in modern metrology is the estimation of uncertainties of measurement in a more consistent manner than applied in the past. This article derives analytical expressions for uncertainties in (x,y), (u,v), and (u′,v′) chromaticity coordinates derived both from direct spectral measurements and from filtered tristimulus colorimeter measurements. Correlations between the tristimulus responses are included. Correlation coefficients are estimated for both broad‐ and narrow‐band sources. Conclusions are drawn for accuracy requirements for spectral matching and for signal‐to‐noise ratios to achieve a particular uncertainty. Specific examples are given for traffic signal lights, light‐emitting diodes, and a luminance standard. © 2000 John Wiley & Sons, Inc. Col Res Appl, 25, 349–355, 2000     

Simulation of daylight for viewing and measuring color

For convenience and reproducibility, daylight is artificially simulated for viewing and measuring colors. Daylight has been standardized in a way that is impractical. the evaluation of fluorescent materials requires simulation of the ultraviolet component of daylight or daylight through a window. Sources for viewing are assessed by spectroradiometry and standard computations. Sources for spectrophotometry may be tested the same way or by measuring radiance factors of fluorescent standards. Better manufacturing methods have improved glass filters. A new filter design method takes account of the spatiospectral nature of the source and affords many degrees of freedom.     

Naming the colors: Color names designation from the colorimetric values. The French GPEM/PV work revisited

This publication describes a work related to the French language, for assigning a color name to an object whose colorimetric characteristics have been measured. This is the subject of a recently published book. The work is the result of an old publication by Afnor, the French standardization organization, work unfortunately obsolete by its colorimetric part. This publication describes the work that has been done to update it and make it convenient to use. The present text, by publishing some of the tables and graphs of the French book, presents the work done in French by a method that differs from that used by Kelly and Judd years ago.     

The use of metamers to compare the color vision of observers

In this research we compare the colorimetric behavior of several observers. For color centers recommended by CIE we have produced large sets of spectral distributions, which are metameric for the CIE 1931 standard observer. For each one of the color centers, we compare the clouds of chromaticity coordinates with the chromaticity thresholds. We define a parameter that provides a quantitative measure of the interobserver variability. This parameter is used to arrange the observers by their degree of likeness. A similar procedure has been used to compare two real observers. It is shown how there is no reciprocity between the colorimetric behavior of two real observers. © 2001 John Wiley & Sons, Inc. Col Res Appl, 26, 262–269, 2001     

An attempt to reconstruct the meaning of al‐Tusi's color words

In a text dating between 1259 and 1277, the Persian scholar al‐Tusi presented a systematic arrangement of 26 color terms. We propose a reconstruction of all color terms from al‐Tusi's scheme, in terms of preferred translation, mean CIEL*a^*b^* coordinates and digital representation. This reconstruction is based on a visual experiment with 30 subjects, who identified the Munsell chip best representing each color term. Persian words for which the meaning changed since the time of al‐Tusi were substituted by direct translations. The results show considerable interobserver variability in the colors selected when identifying color terms. This relatively large variation was shown to be a characteristic for memory matching experiments in general. Several specific color terms for which the resulting color variation was particularly large are discussed in more detail, and possible explanations for these variations are proposed. The proposed reconstruction suggests that al‐Tusi's list is largely consistent in modern colorimetric terms, although some large hue shifts are observed for color terms corresponding to green. We found no evidence for blue‐green (“grue”) confusion. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 206–216, 2016     

An investigation of scotopic threshold-versus-illuminance curves for the analysis of color-matching data

Stiles developed a method for estimating whether rod-photoreceptor activity contributed to color-matching data. This method requires knowledge of the rod threshold at the illuminance levels of lights being viewed. Stiles suggested that the Aguilar and Stiles scotopic threshold-versus-illuminance (TVI) curve could serve as a convenient approximation of the rod threshold. Stiles' method was intended for use in color-matching experiments where the stimuli are presented side by side, but, in the Aguilar and Stiles experiment, detection thresholds were measured for temporally pulsed lights. This study compares rod-sensitivity with detection and side-by-side adjustment tasks. The illumination level of the test and background light was kept below the absolute threshold of the short-wavelength sensitive cones, because there is evidence that cone signals may interact with the scotopic TVI function. The threshold data fell mainly within the range of the Aguilar and Stiles observers. There were two notable deviations from the Aguilar and Stiles curve: (1) consistent with previous reports, the scotopic TVI function had a slope shallower than the Aguilar and Stiles curve when measured with a short-wavelength background; (2) thresholds measured from a dark surround with a spatial adjustment task were higher than the Aguilar and Stiles thresholds even though the slopes were the same. © 1996 John Wiley & Sons, Inc.     

Grassmann's laws and individual color‐matching functions for non‐spectral primaries evaluated by maximum saturation technique in foveal vision

Over time, much work has been carried out to ascertain the validity of Grassmann's laws, Abney's law, CIE standard color‐matching functions and, up to now, no definitive answer has been given. Some of the phenomena subject of this debate are considered. An apparatus for color matching in 1.8° visual field has been realized with two sets of primary lights with broad spectral bands. This kind of primaries is the great difference with respect to other laboratories because it allows an indirect check of the Grassmann additivity law on the basis of the spectra and individual color‐matching functions by evaluating: (1) the tristimulus values of the primary lights; (2) the transformation matrices between the two reference frames defined by the two primary sets; and (3) the tristimulus values associated to all the pairs of matching lights in the bipartite field produced in the evaluation of the two sets of color‐matching function. The discrepancies of the data resulting in the check (1) and (2) are all compatible with the range defined by the uncertainty propagation of the individual color‐matching functions. In the check (3) fifteen tristimulus values over 18 have a discrepancy lower than one standard uncertainty. Grassmann's proportionality law is checked directly by reducing the matching lights with a neutral filter and holds true. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 271–281, 2008.     

Calibrated color mapping between LCD and CRT displays: A case study

The primary goal of a color characterization model is to establish a mapping from digital input values d_i (i = R,G,B) to tristimulus values such as XYZ. A good characterization model should be fast, use a small amount of data, and allow for backward mapping from tristimulus to d_i. The characterization models considered here are for the case of an end user who has no direct knowledge of the internal properties of the display device or its device driver. Three characterization models tested on seven different display devices are presented. The characterization models implemented in this study are a 3D look up table (LUT) (Raja Balasubramanian, Reducing the Cost of Lookup Table Based Color Transformations, Proc IS&T/SID 7th Color Imaging Conference 1 ), a linear model (Fairchild MD, Wyble DR. Colorimetric Characterization of the Apple Studio Display (Flat Panel LCD). Munsell Color Science Laboratory Technical Report, 1998), and the masking model (Tamura N, Tsumura N, Miyake. Masking Model for accurate colorimetric characterization of LCD. Proc IS&T/SID 10th Color Imaging Conference 3 ). The devices include two CRT monitors, three LCD monitors, and two LCD projectors. The results of this study indicate that a simple linear model is the most effective and efficient for all devices used in the study. A simple extension to the linear model is presented, and it is demonstrated that this extension improves white prediction without causing significant errors for other colors. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 438–447, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.     

Color rendering: Asking the question

Two white lights may have the same chromaticity, and yet when used to light an array of objects may differ in their ability to reveal colors. For example, any white light can be matched by a mixture of two narrow‐band lights, a yellow plus a blue. In this extreme case, reds and greens become black or brown and the red‐green dimension is lost. At the other extreme, a light with three narrow bands, at the proper wavelengths, can brighten reds and greens and increase red‐green contrast, relative to a broad‐band light such as daylight. Many commercial lights tend to dull reds and greens, relative to broad‐band sources, a central reason that color rendering is a practical concern. A telling example is neodymium glass, a yellow‐absorbing filter that is sometimes used to improve color rendering. This article seeks to bring these ideas to life through detailed graphical examples. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 403–412, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10193     

Bandwidth correction for LED chromaticity

The spectral bandwidth formulae of Stearns and Stearns   are generalized for an arbitrary slit function. Correction coefficients are derived in terms of moments of the slit function. Application to model LED spectra measured with a compact, fiber‐coupled spectrometer having bandwidth of order 12 nm, and a nonlinear wavelength scale shows that accurate LED color measurements may be obtained with such an instrument. Fitting of the relatively broad slit function to line spectra for accurate wavelength calibration is also described. Such fitting, coupled consistently with the bandpass correction, improves the accuracy color measurements with a broad‐response spectrometer. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 374–380, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20242     

A tetrachromatic model for colorimetric use in mesopic vision

In this article, a tetrachromatic colorimetric model is proposed. Four monochromatic stimuli are used as primaries instead of three to achieve colorimetric matches in mesopic vision. Tetrachromatic colorimetric matches are assumed in such a way so as to hold in both the photopic and the scotopic levels of adaptation. The fourth primary helps to balance the rod contribution in mesopic vision. The proposed model is based on the experimental observations that (a) trichromatic matches can be achieved in any light level and (b) once a tetrachromatic match is made, it holds at all radiances. The main outcome is that (a) only three channels in human vision system are important for color matching at mesopic and photopic levels and (b) additivity can be preserved at all levels once rod input is taken into account. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2011     

铂热电阻不确定度的评定

分析了铂热电阻的标准不确定度和合成不确定度,为铂热电阻在化工企业的测量准确性提供了不确定度的检测方法。     

化工投资项目的不确定性分析

阐述不确定性分析在化工投资项目可行性研究中的重要的性;介绍盈亏平衡分析、敏感性分析、概率分析3种最常用的不确定性分析方法。     

Optimization of LED‐based light blendings for object presentation

This study looks at the perceived quality of light‐emitting diode (LED)‐based lighting of various colors. The objective was to find out whether LEDs could provide better (i.e., more relevant and acceptable) lighting than that which is obtained with standard halogen or fluorescent sources. The perception of objects was assessed under different lighting schemes. Subjects were invited to add red, cyan and/or amber to white LED‐based light to match the halogen and fluorescence rendering on specific targets: a color chart and a painting. They were also asked to rate the difference between the two, and to express their preference. The results obtained for the perception of LED‐based lighting were quite positive. Color blendings of LED light were found to provide illuminated situations similar to halogens or fluorescent sources. These blendings were well accepted, and indeed often preferred, although the color rendering index (CRI) was always low. This indicates that the CRI as it stands is inadequate to characterize the color rendering of solid‐state light sources, and needs to be updated. LED‐based lighting systems seem to have considerable potential for use in shops and display units, where they may well outperform existing lighting systems. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 310–320, 2009     

镧标准溶液配制不确定度的评定

配制100μg/mL镧标准溶液,对配制过程不确定度来源进行分析评定,确定其主要不确定度分量来源于基准物质的称量和标准溶液定容过程。合成了相对标准不确定度,扩展因子k取2,扩展不确定度为0.11μg/mL。对镧标准溶液的均匀性做出分析,实验数据表明,所配制的标准溶液均匀性良好。