Visual versus Instrumental Colour Matching

The paper describes studies that have been made of both visual and instrumental colour matching and attempts to measure those factors that must be taken into account when replacing visual with instrumental colour matching. The factors in visual colour matching examined are lighting source, viewing geometry, size of specimen, age, sex and colour-vision defects of observer, and consistency of observers. Those in instrumental colour matching are lighting source, choice of 2° or 10° Standard Observer data, effect of viewing geometry, textile structure, lustre (or specular reflection), dichroism, fluorescence, metamerism of specimen, choice of colour-difference formulae, and uniformity of visually uniform colour space. Mechanical and electrical reliability of instruments, short-and long-term reproducibility, and absolute and relative accuracies of instruments are discussed.     

Visual and Instrumental Colour Control in the Paper Industry

The way in which a combination of visual and instrumental assessments is used to control the colours of a wide variety of papers is outlined. Some thoughts on the most economical balance between instrumental and visual methods are also given.     

The Measurement and Assessment of Colour Differences for Industrial Use. IV—The Accuracy of Visual Assessments

The magnitude of the errors in the visual assessment of colour differences is discussed. The errors are likely to vary with the particular form of visual assessment. Methods are described for estimating visual errors from data in which the visual assessments are expressed as percentage acceptance and rank orders as well as ratios of other colour differences. The results indicate that experienced observers tend to have a greater degree of discrimination than inexperienced observers. Between-observer variation is greater than within-observer variation, suggesting that the mean of many repeat observations by a single observer may differ significantly from the mean derived from a number of different observers. For colour passing, the error of a single observer varies with the size of the colour difference and is given by the equation: σ=0.4+ 0.25 δν where δν is the true visual difference expressed in units equivalent to the average unit given by the AN40 equation.     

The Measurement and Assessment of Colour Differences for Industrial Use V—The Accuracy of Visual Assessments in Relation to Industrial Colour Passing

The quantitative data available for expressing the errors associated with visual assessments, measurements and colour-difference equations have been used to calculate, for given sets of circumstances, the pass and rejection rates at various stages from the dyer to the retailer to the final customer. The main errors arise in the visual assessments and the colour-difference equations and, for the average of the available equations, these two errors are roughly comparable in magnitude. They do, however, vary with size of colour difference in different ways such that for small differences (0- 1AN40 units) the equations agree better with the true colour differences than a single visual assessment, whereas the reverse is true for large differences (above 2 AN40 units). Detailed results depend on the distribution of samples over the range of colour differences considered, together with the sizes of colour-tolerance limits set. Two initial distributions for the dyer have been assumed, one with same number of samples at all colour differences and the other simulating the distribution used in the Davidson and Friede study. For each, the results of use of a ‘low tolerance’ (0.5 AN40 unit) and a ‘high tolerance’ (1.5 AN40 units) by the dyer have been calculated. At low tolerance, the average equation provides much greater satisfaction than one assessor and improved equations will not give much more satisfaction. At high tolerance, the average equation could give greater or less satisfaction depending on the precision of the particular assessor and the exact distribution of samples to be considered, but there are considerable benefits to be gained by improvement in equation performance. Some of the likely interactions between the dyer and his customers are illustrated, showing that difficulties could arise unless there is some degree of co-operation. This is particularly true if unilateral action for equation use is taken by the retailer working to his customary tolerance limit. It would appear that the introduction of the use of an equation should first be made by the dyer, but if made by the retailer then consultation with the dyer is essential. The use of an equation by a retailer provides little benefit except in reducing dyer-retailer disputes.     

白度的目视评价和仪器度量

概述了非彩色的中性白,介绍了白度的目视评价和仪器度量,评述了目前常用的白度公式。     

色差的测量及其不确定度的评定

介绍了颜色的测量及其表示方法,以及常用的色差计算方法。简述了不确定度的定义及评定方法。通过白色色板的测定对仪器测定色差进行了不确定度的评定。     

A Guide to the Measurement of Colour and Colour Differences with Photoelectric Tristimulus Colorimeters

Recommendations are made for the measurement of colour and colour differences with photoelectric tristimulus colorimeters. Instrument standardisation, measurements on one sample, measurement of colour differences and procedures of sample presentation and measurement are discussed. Finally, a recommended procedure is detailed.     

Measurement and Assessment of Colour Differences for Industrial Use I—The Reproducibility and Repeatability of Colour-difference Measurements

The precision of measurements obtainable with several types of colorimeter (Colormaster Marks IV and V, Small Sphere Color-Eye DI, Colorcord Mk IIA, Harrison 61 and Harrison 70) for several substrates (ceramic tiles, fabrics, yarns and threads, loose stock, slubbing and plain carpet) has been studied. Several methods of preparation and presentation of the sample to an instrument are considered and the results are compared in terms of standard deviations in 1964 (CIE) units. For textile samples the most generally satisfactory technique is to present the prepared sample behind glass in a rotating head. Under these conditions a wide range of fabrics can be measured with approximately the same precision (0<1 CIE) as ceramics. For yarns and threads, carefully wound on formers, the precision is approximately 0<3 CIE, and a slightly better precision can be obtained for carpets. Values of < 0<3 have been obtained for loose stock using a special rotating head, but values for slubbing are somewhat worse (0<8–1<0). Except for the Colorcord, good between-instrument reproducibility (< 0<3 CIE) can be obtained for measurements of colour differences. For a given sample the absolute values (X, Y, Z) vary considerably with the instrument, the differences between pairs of instruments being equivalent to several CIE units and up to 19 when the Harrison 70 is used, even for measurements on a ceramic tile.     

Small and Moderate Colour Differences

In nineteen regions of colour space groups of about 30 samples, differing by small to moderate amounts from one designated as ‘the standard’ were generated by offset printing. Twenty observers estimated the perceived size of each of these differences twice, using cateogry scaling - the judgements were not based on acceptability. The samples were placed, in turn, adjacent to the standard on a middle gray surround, subtended 4d? on the retina, were illuminated with semidiffuse fluorescent light, simulating daylight at about 45d? incidence, and viewed along the normal. The visual data were converted from an ordinal to an interval scale. The samples were measured by abridged spectro-photometry, and CIE coordinates, obtained by integration using the spectral-power distribution of the illumination source and the 1931 2d? standard observer. Colour differences were calculated by eleven formulae and correlated with the visual interval-scale results. The usual low correlation coefficients were found. The data are analysed colour by colour and significant differences are noted. Collectively, the Adams Chromatic Value (ANL AB 40), Saunderson-Milner, and CIE 1976 L*a*b* formulae gave better performances.     

An Introduction to Instrumental Measurements of Colour Difference in Relation to Colour Tolerance

The visual assessment of small colour differences still plays a large part in the determination of the acceptability of industrial products, particularly textiles. For several reasons, which are discussed, many advantages would accrue from the replacement of visual methods by instrumental ones. The general features of both visual assessment and instrumental measurement are given, and the types of approach in attempts to correlate the twoare discussed. Visual assessments vary greatly, depending on the viewing conditions, so several different correlations have been made in the form of colour-difference equations. Although a particular equation might provide a good correlation for particular viewing conditions, the usual conditions under which the better-known equations have been established do not correspond to those used in industry. These points have been elaborated to provide the relevant background to the report of work carried out under the direction of the Society's Colour Measurement Committee.     

影响煤炭发热量测定准确度的因素

在分析煤质项目中,测定其发热量是一个关键内容,不仅是动力煤有效评估的质量指标,也可以为分析煤质改变规律提供参考。由于不断提升了量热仪设备的自动化水平,大多数实验室已经采用更加精密的设备,却明显忽略了操作性。不管多么精密的设备,若无法准确适用,也不会得到标准结果。结合煤炭发热量测定实验,对结果准确度造成影响的因素进行整体分析,希望可以提升测定水平。     

Colour Measurement and Colour Tolerance in the Plastics Industry

The limited use, within the plastics industry, of colour-difference units is discussed. The requirements and calibration of measuring instruments, with particular reference to plastics, are stated, together with details of reference and calibration standards. Identification and estimation of colorants is carried out with the Comic analogue computer handling a modified Kubelka—Munk function of the spectrophotometric reflectance curve. Although the scatter component of this function varies with the opacity of the moulding, the variation can be predicted and its effect nullified. The correction of a first prediction for a new colour is done through the computer by means of the differences in tristimulus values, as measured by means of a colorimeter, between the predicted recipe and the required colour. An extension of this method for colour control in production is explained. The colour tolerances achieved by instrumental control in the production of thermosetting plastics are stated in terms of the deviation (in MacAdam units) from standard. The colour gamut over which measurement may usefully be applied is prescribed. Finally, some problems associated with measurement are described, together with their solutions.     

Colour Measurement of Human Teeth and Evaluation of a Colour Guide

In the present work the colour coordinates have been obtained in the CIELAB system (L*,a*,b*) for the teeth of 600 individuals. to determine the region of the CIELAB space which contains all the different hues found in human teeth. In addition. one of the colour guides most used in dentistry has been studied to compare the hue range in this guide with the range possible in human teeth. The results show that colour coordinates of human teeth fall within an elliptical contour centered in a yellowish white. The colour guide studied did not cover all the possible values found for teeth chromaticities.     

Instrumental Colour Prediction A Potential Aid to Dye and Process Selection

A relationship has been established between the dyeing properties of fibre–reactive dyes and the spectral reflectance properties of the colours produced on machine–washable wool. The information gained in routine dye calibration for instrumental colour–prediction systems may be used by the practical dyer for dye selection. The spectral reflectance properties of the resultant dyeings are explained in terms of the diffusion, fixation and level–dyeing properties of specific fibre–reactive dyes applied to wool by exhaust and pad–dyeing processes.     

The Application of Colour Measurement

Earlier review papers by Hunt [I] and McLaren [2] have dealt with the basic principles of colour measurement and its application to the measurement of colour difference, respectively. This paper is mainly an attempt to assess the present situation on instrumental recipe prediction, but it also includes topics such as whiteness and fluorescence, metamerism, blends of coloured fibres, and the production of colour-separation transparencies in printing. Colour differences are used at various stages of the recipe prediction procedure.     

The Role of Instrumental Colour Control in the Optimization of Dyehouse Performance

The paper describes the general techniques used and the results obtained in pilot plant and commercial dye-house experiments carried out to demonstrate the potential of an inhouse spectrophotometer and minicomputer system in:

• 1 high-accuracy recipe prediction to produce bulk dyehouse recipes without laboratory check dyeing
• 2 calculation of redye procedures to correct off-shade bulk dyeing
• 3 control of dyehouse pass/fail matching by instrumental methods
• 4 preparation of recipe cards, druglines and cost information by computer methods.