1、Designation: D2244 15aD2244 16Standard Practice forCalculation of Color Tolerances and Color Differences fromInstrumentally Measured Color Coordinates1This standard is issued under the fixed designation D2244; the number immediately following the designation indicates the year oforiginal adoption or
2、, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.INTRO
3、DUCTIONThis practice originally resulted from the consolidation of a number of separately publishedmethods for the instrumental evaluation of color differences.As revised in 1979, it included four colorspaces in which color-scale values could be measured by instruments, many of which were obsolete,a
4、nd the color differences calculated by ten equations for different color scales. The sections onapparatus, calibration standards and methods, and measurement procedures served little purpose in thelight of modern color-measurement technology. The revision published in 1993 omitted these sections,and
5、 limited the color spaces and color-difference equations considered, to the three most widely usedin the paint and related coatings industry.Aprevious revision added two new color tolerance equationsand put two of the color difference equations from the 1993 version in an informative appendix forhis
6、torical purposes.1. Scope*1.1 This practice covers the calculation, from instrumentally measured color coordinates based on daylight illumination, ofcolor tolerances and small color differences between opaque specimens such as painted panels, plastic plaques, or textile swatches.Where it is suspecte
7、d that the specimens may be metameric, that is, possess different spectral curves though visually alike in color,Practice D4086 should be used to verify instrumental results. The tolerances and differences determined by these procedures areexpressed in terms of approximately uniform visual color per
8、ception in CIE 1976 CIELAB opponent-color space (1),2 CMCtolerance units (2), CIE94 tolerance units (3), the DIN99 color difference formula given in DIN 6176(4), or the new CIEDE2000color difference units (5).1.2 For product specification, the purchaser and the seller shall agree upon the permissibl
9、e color tolerance between testspecimen and reference and the procedure for calculating the color tolerance. Each material and condition of use may requirespecific color tolerances because other appearance factors, (for example, specimen proximity, gloss, and texture), may affect thecorrelation betwe
10、en the magnitude of a measured color difference and its commercial acceptability.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and de
11、termine the applicability of regulatoryrequirements prior to use.2. Referenced Documents2.1 ASTM Standards:3D1729 Practice for Visual Appraisal of Colors and Color Differences of Diffusely-Illuminated Opaque MaterialsD4086 Practice for Visual Evaluation of MetamerismE284 Terminology of Appearance1 T
12、his practice is under the jurisdiction of ASTM Committee E12 on Color and Appearance and is the direct responsibility of Subcommittee E12.04 on Color andAppearance Analysis.Current edition approved Aug. 1, 2015July 1, 2016. Published August 2015July 2016. Originally approved in 1964. Last previous e
13、dition approved in 2015 asD2244 15D2244 15a.1. DOI: 10.1520/D2244-15A.10.1520/D2244-16.2 The boldface numbers in parentheses refer to the list of references at the end of this standard.3 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm
14、.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
15、it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears
16、at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1E308 Practice for Computing the Colors of Objects by Using the CIE SystemE805 Practice for Identification of Instrumental Methods of Color or Color-Difference
17、Measurement of MaterialsE1164 Practice for Obtaining Spectrometric Data for Object-Color Evaluation2.2 Other Standards:DIN 6176 Farbmetrische, Bestimmung von Farbabstnden bei Krperfarben nach der DIN99-Formel 43. Terminology3.1 Terms and definitions in Terminology E284 are applicable to this practic
18、e.3.2 Definitions of Terms Specific to This Standard:3.2.1 colorimetric spectrometer, nspectrometer, one component of which is a dispersive element (such as a prism, grating orinterference filter or wedge or tunable or discrete series of monochromatic sources), that is normally capable of producing
19、as outputcolorimetric data (such as tristimulus values and derived color coordinates or indices of appearance attributes). Additionally, thecolorimetric spectrometer may also be able to report the underlying spectral data from which the colorimetric data were derived.3.2.1.1 DiscussionAt one time, U
20、V-VIS analytical spectrophotometers were used for colorimetric measurements. Today, while instruments intendedfor use in color measurements share many common components, UV-VIS analytical spectrophotometers are designed to optimizetheir use in chemometric quantitative analysis, which requires very p
21、recise spectral position and very narrow bandpass andmoderate baseline stability. Colorimetric spectrometers are designed to optimize their use as digital simulations of the visualcolorimeter or as the source of spectral and colorimetric information for computer-assisted color matching systems. Digi
22、talcolorimetry allows more tolerance on the spectral scale and spectral bandwidth but demand much more stability in the radiometricscale.3.2.2 color tolerance equation, na mathematical expression, derived from acceptability judgments, which distorts the metricof color space based on the coordinates
23、in that color space, of a reference color, for the purpose of single number shade passing.3.2.2.1 DiscussionThe color tolerance equation computes a pass/fail value based on which of the pair of specimens is assigned the designation“standard.” Thus, inter-changing the reference and test specimens wil
24、l result in a change in the predicted level of acceptancebetween the specimens while the perceived difference is unchanged.Acolor difference equation quantifies distance in a color spaceusing the metric of that space. Inter-changing the reference and test specimens does not change either the perceiv
25、ed or predictedcolor differences.4. Summary of Practice4.1 The differences in color between a reference and a test specimen are determined from measurements made by use of aspectral based or filter based colorimeter. Reflectance readings from spectral instruments are converted by computations tocolo
26、r-scale values in accordance with Practice E308, or these color-scale values may be read directly from instruments thatautomatically make the computations. Color-difference units are computed, from these color-scale values, and approximate theperceived color differences between the reference and the
27、 test specimen.5. Significance and Use5.1 The original CIE color scales based on tristimulus values X, Y, Z and chromaticity coordinates x, y are not uniform visually.Each subsequent color scale based on CIE values has had weighting factors applied to provide some degree of uniformity so thatcolor d
28、ifferences in various regions of color space will be more nearly comparable. On the other hand, color differences obtainedfor the same specimens evaluated in different color-scale systems are not likely to be identical. To avoid confusion, colordifferences among specimens or the associated tolerance
29、s should be compared only when they are obtained for the same color-scalesystem. There is no simple factor that can be used to convert accurately color differences or color tolerances in one system todifference or tolerance units in another system for all colors of specimens.5.2 Color differences ca
30、lculated in ECMC or E00 units are highly recommended for use with color-differences in the range of0.0 to 5.0 E*ab units. Both are appropriate for and widely used in industrial and commercial applications including, but notlimited to, automobiles, coatings, cosmetics, inks, packaging, paints, plasti
31、cs, printing, security, and textiles. The Hunter colordifference components LH, aH, bH, and their color difference unit EH, are used by the coil coating and aluminum extrusioncoating industries, as well as the customers of these users. They are, therefore, included in Appendix X1 for historical purp
32、osesand use.4 Available from Beuth Verlag GmbH, 10772, Berlin, Germany, http:/www.beuth.de/.D2244 1625.3 Users of color tolerance equations have found that, in each system, summation of three, vector color-difference componentsinto a single scalar value is very useful for determining whether a speci
33、men color is within a specified tolerance from a standard.However, for control of color in production, it may be necessary to know not only the magnitude of the departure from standardbut also the direction of this departure. It is possible to include information on the direction of a small color di
34、fference by listingthe three instrumentally determined components of the color difference.5.4 Selection of color tolerances based on instrumental values should be carefully correlated with a visual appraisal of theacceptability of differences in hue, lightness, and saturation obtained by using Pract
35、ice D1729. The three tolerance equations givenhere have been tested extensively against such data for textiles and plastics and have been shown to agree with the visualevaluations to within the experimental uncertainty of the visual judgments. That implies that the equations themselves misclassifya
36、color difference with a frequency no greater than that of the most experienced visual color matcher.5.5 While color difference equations and color tolerance equations are routinely applied to a wide range of illuminants, theyhave been derived or optimized, or both, for use under daylight illuminatio
37、n. Good correlation with the visual judgments may notbe obtained when the calculations are made with other illuminants. Use of a tolerance equation for other than daylight conditionswill require visual confirmation of the level of metamerism in accordance with Practice D4086.6. Description of Color-
38、Difference and Color-Tolerance Equations6.1 CIE 1931 and 1964 Color SpacesThe daylight colors of opaque specimens are represented by points in a space formedby three rectangular axes representing the lightness scale Y and chromaticity scales x and y, where:x 5 XX1Y1Z (1)y 5 YX1Y1Z (2)where X,Y, and
39、Z are tristimulus values for either the 1931 CIE standard observer (2 observer) or the 1964 CIE standardobserver (10 observer) and standard illuminant D65, or other phase of daylight. These scales do not provide a perceptually uniformcolor space. Consequently, color differences are seldom if ever co
40、mputed directly from differences in x, y, and Y.6.2 CIE 1976 L* a* b* Uniform Color Space and Color-Difference Equation (1, 6)This is an approximately uniform colorspace based on nonlinear expansion of the tristimulus values and taking differences to produce three opponent axes thatapproximate the p
41、ercepts of lightness-darkness, redness-greenness and yellowness-blueness. It is produced by plotting inrectangular coordinates the quantities L*, a*, b*, calculated as follows:L*5116 f QY! 216 (3)a*5500 f QX! 2f QY! # (4)b*5200 f QY! 2f QZ! # (5)whereQX 5X/Xn!;QY 5Y/Yn!;QZ 5Z/Zn!andfQi! 5Qi1/3 if Qi
42、.6/29!3elsefQi! 5841/108!Qi14/29 if Qi#6/29!3.Here, i varies as X, Y, and Z.The tristimulus values Xn,Yn,Zn define the color of the nominally white object-color stimulus. Usually, the white object-colorstimulus is given by the spectral radiant power of one of the CIE standard illuminants, for exampl
43、e, C,D65 or another phase ofdaylight, reflected into the observers eye by the perfect reflecting diffuser. Under these conditions, Xn,Yn,Zn are the tristimulusvalues of the standard illuminant with Yn equal to 100.6.2.1 The total color-difference Eab* between two colors each given in terms of L*, a*
44、, b* is calculated as follows:E*ab 5=L*! 21a*!21b*! 2 (6)NOTE 1The color space defined above is called the CIE 1976 L* a * b* space and the color-difference equation the CIE 1976 L* a* b*color-difference formula. The abbreviation CIELAB (with all letters capitalized) is recommended.6.2.2 The magnitu
45、de, E*ab, gives no indication of the character of the difference since it does not indicate the relative quantityand direction of hue, chroma, and lightness differences.6.2.3 The direction of the color difference is described by the magnitude and algebraic signs of the components L*, a*, andb*:L*5L*
46、B 2L* S (7)a*5a*B 2a*S (8)D2244 163b*5b*B 2b*S (9)where L*S, a*S, and b*S refer to the reference or standard, and L*B, a*B , and b*B refer to the test specimen or batch. The signsof the components L*, a*, and b* have the following approximate meanings (7):1L*5lighter (10)2L*5darker (11)1a*5redder le
47、ss green! (12)2a*5greener less red! (13)1b*5yellow less blue! (14)2b*5bluer less yellow! (15)6.2.4 For judging the direction of the color difference between two colors, it is useful to calculate hue angles hab and CIE 1976metric chroma C*ab according to the following pseudocode:if b* 50then (16)hab5
48、90 signa*!signa*!21#elsehab51802180/!arctana*/b*!290signb*!end if.Here sign is a function that returns the sign of the argument, and arctan is the inverse tangent function returning angles in unitsof radians. The units of hab calculated by the above are degrees counter-clockwise from the positive a*
49、 axis. The function sign isexpected to return a minus one for negative values of the argument, a zero when the argument is zero, and a positive one forpositive values of the argument.C*ab5=a*!21b*!2 (17)Differences in hue angle hab between the test specimen and reference can be correlated with differences in their visuallyperceived hue, except for very dark colors (8). Differences in chroma C*ab = (C*abbatch C*abstandard) can similarly becorrelated with differences in visually perceived chroma.6.2.
