1、Designation: D2244 15aStandard 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, in the
2、 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.INTRODUCTIONT
3、his 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,and the c
4、olor 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 limited
5、 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 forhistorical
6、purposes.1. Scope*1.1 This practice covers the calculation, from instrumentallymeasured color coordinates based on daylight illumination, ofcolor tolerances and small color differences between opaquespecimens such as painted panels, plastic plaques, or textileswatches. Where it is suspected that the
7、 specimens may bemetameric, that is, possess different spectral curves thoughvisually alike in color, Practice D4086 should be used to verifyinstrumental results. The tolerances and differences determinedby these procedures are expressed in terms of approximatelyuniform visual color perception in CI
8、E 1976 CIELABopponent-color space (1),2CMC tolerance units (2), CIE94tolerance units (3), the DIN99 color difference formula givenin DIN 6176(4), or the new CIEDE2000 color difference units(5).1.2 For product specification, the purchaser and the sellershall agree upon the permissible color tolerance
9、 between testspecimen and reference and the procedure for calculating thecolor tolerance. Each material and condition of use may requirespecific color tolerances because other appearance factors, (forexample, specimen proximity, gloss, and texture), may affectthe correlation between the magnitude of
10、 a measured colordifference and its commercial acceptability.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-
11、bility of regulatory requirements prior to use.2. Referenced Documents2.1 ASTM Standards:3D1729 Practice for Visual Appraisal of Colors and ColorDifferences of Diffusely-Illuminated Opaque MaterialsD4086 Practice for Visual Evaluation of MetamerismE284 Terminology of AppearanceE308 Practice for Comp
12、uting the Colors of Objects by Usingthe CIE SystemE805 Practice for Identification of Instrumental Methods ofColor or Color-Difference Measurement of MaterialsE1164 Practice for Obtaining Spectrometric Data for Object-Color Evaluation1This practice is under the jurisdiction of ASTM Committee E12 on
13、Color andAppearance and is the direct responsibility of Subcommittee E12.04 on Color andAppearance Analysis.Current edition approved Aug. 1, 2015. Published August 2015. Originallyapproved in 1964. Last previous edition approved in 2015 as D2244 151. DOI:10.1520/D2244-15A.2The boldface numbers in pa
14、rentheses refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM
15、website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States12.2 Other Standards:DIN 6176 Farbmetrische, Bestimmung von Farbabstndenbei Krperfarben nach der DIN99-Formel43. T
16、erminology3.1 Terms and definitions in Terminology E284 are appli-cable to this practice.3.2 Definitions of Terms Specific to This Standard:3.2.1 colorimetric spectrometer, nspectrometer, one com-ponent of which is a dispersive element (such as a prism,grating or interference filter or wedge or tuna
17、ble or discreteseries of monochromatic sources), that is normally capable ofproducing as output colorimetric data (such as tristimulusvalues and derived color coordinates or indices of appearanceattributes). Additionally, the colorimetric spectrometer mayalso be able to report the underlying spectra
18、l data from whichthe colorimetric data were derived.3.2.1.1 DiscussionAt one time, UV-VIS analytical spec-trophotometers were used for colorimetric measurements.Today, while instruments intended for use in color measure-ments share many common components, UV-VIS analyticalspectrophotometers are desi
19、gned to optimize their use inchemometric quantitative analysis, which requires very precisespectral position and very narrow bandpass and moderatebaseline stability. Colorimetric spectrometers are designed tooptimize their use as digital simulations of the visual colorim-eter or as the source of spe
20、ctral and colorimetric informationfor computer-assisted color matching systems. Digital colorim-etry allows more tolerance on the spectral scale and spectralbandwidth but demand much more stability in the radiometricscale.3.2.2 color tolerance equation, na mathematicalexpression, derived from accept
21、ability judgments, which dis-torts the metric of color space based on the coordinates in thatcolor space, of a reference color, for the purpose of singlenumber shade passing.3.2.2.1 DiscussionThe color tolerance equation computesa pass/fail value based on which of the pair of specimens isassigned th
22、e designation “standard.” Thus, inter-changing thereference and test specimens will result in a change in thepredicted level of acceptance between the specimens while theperceived difference is unchanged. A color difference equationquantifies distance in a color space using the metric of thatspace.
23、Inter-changing the reference and test specimens does notchange either the perceived or predicted color differences.4. Summary of Practice4.1 The differences in color between a reference and a testspecimen are determined from measurements made by use of aspectral based or filter based colorimeter. Re
24、flectance readingsfrom spectral instruments are converted by computations tocolor-scale values in accordance with Practice E308, or thesecolor-scale values may be read directly from instruments thatautomatically make the computations. Color-difference unitsare computed, from these color-scale values
25、, and approximatethe perceived color differences between the reference and thetest specimen.5. Significance and Use5.1 The original CIE color scales based on tristimulusvalues X, Y, Z and chromaticity coordinates x, y are not uniformvisually. Each subsequent color scale based on CIE values hashad we
26、ighting factors applied to provide some degree ofuniformity so that color differences in various regions of colorspace will be more nearly comparable. On the other hand, colordifferences obtained for the same specimens evaluated indifferent color-scale systems are not likely to be identical. Toavoid
27、 confusion, color differences among specimens or theassociated tolerances should be compared only when they areobtained for the same color-scale system. There is no simplefactor that can be used to convert accurately color differencesor color tolerances in one system to difference or toleranceunits
28、in another system for all colors of specimens.5.2 Color differences calculated in ECMCor E00units arehighly recommended for use with color-differences in therange of 0.0 to 5.0 E*abunits. Both are appropriate for andwidely used in industrial and commercial applicationsincluding, but not limited to,
29、automobiles, coatings, cosmetics,inks, packaging, paints, plastics, printing, security, and textiles.The Hunter color difference components LH, aH, bH, andtheir color difference unit EH, are used by the coil coating andaluminum extrusion coating industries, as well as the custom-ers of these users.
30、They are, therefore, included in AppendixX1 for historical purposes and use.5.3 Users of color tolerance equations have found that, ineach system, summation of three, vector color-differencecomponents into a single scalar value is very useful fordetermining whether a specimen color is within a speci
31、fiedtolerance from a standard. However, for control of color inproduction, it may be necessary to know not only the magni-tude of the departure from standard but also the direction ofthis departure. It is possible to include information on thedirection of a small color difference by listing the thre
32、einstrumentally determined components of the color difference.5.4 Selection of color tolerances based on instrumentalvalues should be carefully correlated with a visual appraisal ofthe acceptability of differences in hue, lightness, and saturationobtained by using Practice D1729. The three tolerance
33、 equa-tions given here have been tested extensively against such datafor textiles and plastics and have been shown to agree with thevisual evaluations to within the experimental uncertainty of thevisual judgments. That implies that the equations themselvesmisclassify a color difference with a freque
34、ncy no greater thanthat of the most experienced visual color matcher.5.5 While color difference equations and color toleranceequations are routinely applied to a wide range of illuminants,they have been derived or optimized, or both, for use underdaylight illumination. Good correlation with the visu
35、al judg-ments may not be obtained when the calculations are madewith other illuminants. Use of a tolerance equation for otherthan daylight conditions will require visual confirmation of thelevel of metamerism in accordance with Practice D4086.4Available from Beuth Verlag GmbH, 10772, Berlin, Germany
36、, http:/www.beuth.de/.D2244 15a26. Description of Color-Difference and Color-ToleranceEquations6.1 CIE 1931 and 1964 Color SpacesThe daylight colorsof opaque specimens are represented by points in a spaceformed by three rectangular axes representing the lightnessscale Y and chromaticity scales x and
37、 y, where:x 5XX1Y1Z(1)y 5YX1Y1Z(2)where X, Y, and Z are tristimulus values for either the 1931CIE standard observer (2 observer) or the 1964 CIE standardobserver (10 observer) and standard illuminant D65, or otherphase of daylight. These scales do not provide a perceptuallyuniform color space. Conse
38、quently, color differences are sel-dom if ever computed 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 uniformcolor space based on nonlinear expansion of the tristimulusvalues and taking differences to p
39、roduce three opponent axesthat approximate the percepts of lightness-darkness, redness-greenness and yellowness-blueness. It is produced by plottingin rectangular coordinates the quantities L*, a*, b*, calculatedas follows:L* 5 116 f QY! 2 16 (3)a* 5 500 f QX! 2 f QY! # (4)b* 5 200 f QY! 2 f QZ! # (
40、5)whereQX5 X/Xn!; QY5 Y/Yn!; QZ5 Z/Zn!andfQi! 5 Qi1/3if Qi.6/29!3elsefQi! 5 841/108!Qi14/29 if Qi# 6/29!3.Here, i varies as X, Y, and Z.The tristimulus values Xn, Yn, Zndefine the color of thenominally white object-color stimulus. Usually, the whiteobject-color stimulus is given by the spectral radi
41、ant power ofone of the CIE standard illuminants, for example, C, D65oranother phase of daylight, reflected into the observers eye bythe perfect reflecting diffuser. Under these conditions, Xn, Yn,Znare the tristimulus values of the standard illuminant with Ynequal to 100.6.2.1 The total color-differ
42、ence Eab* between two colorseach given in terms of L*, a*, b* is calculated as follows:E*ab5 =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
43、letterscapitalized) is recommended.6.2.2 The magnitude, E*ab, gives no indication of thecharacter of the difference since it does not indicate the relativequantity and direction of hue, chroma, and lightness differ-ences.6.2.3 The direction of the color difference is described bythe magnitude and al
44、gebraic signs of the components L*,a*, and b*:L* 5 L*B2 L*S(7)a* 5 a*B2 a*S(8)b* 5 b*B2 b*S(9)where L*S, a*S, and b*Srefer to the reference or standard,and L*B, a*B, and b*Brefer to the test specimen or batch. Thesigns of the components L*, a*, and b* have the followingapproximate meanings (7):1L* 5
45、 lighter (10)2 L* 5 darker (11)1a* 5 redder less green! (12)2a* 5 greener less red! (13)1b* 5 yellow less blue! (14)2 b* 5 bluer less yellow! (15)6.2.4 For judging the direction of the color differencebetween two colors, it is useful to calculate hue angles habandCIE 1976 metric chroma C*abaccording
46、 to the followingpseudocode:if b* 5 0 then (16)hab5 90 signa*! signa*! 2 1#elsehab5 180 2 180/!arctana*/b*! 2 90 signb*!end if.Here sign is a function that returns the sign of the argument,and arctan is the inverse tangent function returning angles inunits of radians. The units of habcalculated by t
47、he above aredegrees counter-clockwise from the positive a* axis. Thefunction sign is expected to return a minus one for negativevalues of the argument, a zero when the argument is zero, anda positive one for positive values of the argument.C*ab5 =a*!21b*!2(17)Differences in hue angle habbetween the
48、test specimen andreference can be correlated with differences in their visuallyperceived hue, except for very dark colors (8). Differences inchroma C*ab=(C*abbatchC*abstandard) can similarly becorrelated with differences in visually perceived chroma.6.2.5 For judging the relative contributions of li
49、ghtnessdifferences, chroma differences, and hue differences betweentwo colors, it is useful to calculate the CIE 1976 Metric HueDifference H*abbetween the colors as follows: H*ab5 s 2C*ab,BC*ab,S2 a*Ba*S2 b*Bb*S!#0.5(18)whereif a*Sb*B.a*Bb*Sthen (19)s 5 1elses 521end if.D2244 15a3When E*abis calculated as in 6.2.1 and C*abis calculatedas in 6.2.4, thenE*ab5 L*!21C*!21H*!2#0.5(20)contains terms showing the relative contributions of light-ness differences L*ab, chroma differences C*ab,
