ASTM D2244-2007e1 Standard Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Color Coordinates.pdf

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1、Designation: D 2244 071Standard Practice forCalculation of Color Tolerances and Color Differences fromInstrumentally Measured Color Coordinates1This standard is issued under the fixed designation D 2244; the number immediately following the designation indicates the year oforiginal adoption or, in t

2、he 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 Department of Defense.1NOTEEquation 28

3、 was corrected editorially in November 2008.INTRODUCTIONThis 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 measu

4、red by instruments, many of which were obsolete,and 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 revi

5、sion published in 1993 omitted these sections,and 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 t

6、he 1993 version in an informative appendix forhistorical 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 pl

7、aques, or textileswatches. Where it is suspected that the specimens may bemetameric, that is, possess different spectral curves thoughvisually alike in color, Practice D 4086 should be used to verifyinstrumental results. The tolerances and differences determinedby these procedures are expressed in t

8、erms of approximatelyuniform visual color perception in CIE 1976 CIELABopponent-color space (1)2, CMC 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 an

9、d the sellershall agree upon the permissible color tolerance 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

10、texture), may affectthe correlation between the magnitude of 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-p

11、riate safety and health practices and determine the applica-bility of regulatory requirements prior to use.2. Referenced Documents2.1 ASTM Standards:3D 1729 Practice for Visual Appraisal of Colors and ColorDifferences of Diffusely-Illuminated Opaque MaterialsD 4086 Practice for Visual Evaluation of

12、MetamerismE 284 Terminology of AppearanceE 308 Practice for Computing the Colors of Objects byUsing the CIE SystemE 805 Practice for Identification of Instrumental Methods ofColor or Color-Difference Measurement of MaterialsE 1164 Practice for Obtaining Spectrometric Data forObject-Color Evaluation2

13、.2 Other Standards:1This practice is under the jurisdiction of ASTM Committee E12 on Color andAppearance and is the direct responsibility of Subcommittee E12.04 on Color andAppearance Analysis.Current edition approved May 1, 2007. Published May 2007. Originallyapproved in 1964. Last previous edition

14、 approved in 2005 as D 2244 05.2The boldface numbers in parentheses 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

15、, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.DIN 6176 Farbmetrische, Bestimmung von Farbabstndenbe

16、i Krperfarben nach der DIN99-Formel43. Terminology3.1 Terms and definitions in Terminology E 284 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,gratin

17、g or interference filter or wedge or tunable 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

18、 be able to report the underlying spectral data from whichthe colorimetric data were derived.3.2.1.1 DiscussionAt one time, UV-VIS analytical spec-trophotometers were used for colorimetric measurements. To-day, while instruments intended for use in color measurementsshare many common components, UV-

19、VIS analytical spectro-photometers are designed to optimize their use in chemometricquantitative analysis, which requires very precise spectralposition and very narrow bandpass and moderate baselinestability. Colorimetric spectrometers are designed to optimizetheir use as digital simulations of the

20、visual colorimeter or asthe source of spectral and colorimetric information forcomputer-assisted color matching systems. Digital colorimetryallows more tolerance on the spectral scale and spectralbandwidth but demand much more stability in the radiometricscale.3.2.2 color tolerance equation, na math

21、ematical expres-sion, derived from acceptability judgments, which distorts themetric of color space based on the coordinates in that colorspace, of a reference color, for the purpose of single numbershade passing.3.2.2.1 DiscussionThe color tolerance equation computesa pass/fail value based on which

22、 of the pair of specimens isassigned the 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 colo

23、r space using the metric of thatspace. 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 aspectra

24、l based or filter based colorimeter. Reflectance readingsfrom spectral instruments are converted by computations tocolor-scale values in accordance with Practice E 308, or thesecolor-scale values may be read directly from instruments thatautomatically make the computations. Color-difference unitsare

25、 computed, from these color-scale values, 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 c

26、olor scale based on CIE values hashad weighting 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

27、 are not likely to be identical. Toavoid 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

28、 system to difference or toleranceunits in another system for all colors of specimens.5.2 For uniformity of practice, the CIE recommended in1976 the use of two color metrics. The CIELAB metric, withits associated color-difference equation, has found wide accep-tance in the coatings, plastics, textil

29、es and related industries.While the CIELAB equation has not completely replaced theuse of Hunter LH,aH,bH, this older scale is no longerrecommended for other than legacy users, and is thereforeincluded in an Appendix for historical purposes. The CIELABcolor-difference equation is also not recommende

30、d in thispractice for use in describing small and moderate colordifferences (differences with magnitude less than 5.0 D E*abunits). The four more recently defined equations, documentedhere, are highly recommended for use with color-differences inthe range of 0.0 to 5.0 DE*abunits.5.3 Users of color

31、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 specifiedtolerance from a standard. However, for control of color inproduction, it may be necessary

32、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 threeinstrumentally determined components of the color difference.5.4 Selection of color tolerances

33、 based on instrumentalvalues should be carefully correlated with a visual appraisal ofthe acceptability of differences in hue, lightness, and saturationobtained by using Practice D 1729. The three tolerance equa-tions given here have been tested extensively against such datafor textiles and plastics

34、 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 frequency no greater thanthat of the most experienced visual color matcher.5.5 While color differenc

35、e 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 visual judg-ments may not be obtained when the calculations are madewith other illuminants. Use of

36、 a tolerance equation for otherthan daylight conditions will require visual confirmation of thelevel of metamerism in accordance with Practice D 4086.4Available from Beuth Verlag GmbH, 10772 Berlin, Germany.D224407126. Description of Color-Difference and Color-ToleranceEquations6.1 CIE 1931 and 1964

37、 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 y, where:x 5XX 1 Y 1 Z(1)y 5YX 1 Y 1 Z(2)where X, Y, and Z are tristimulus values for either the 1931CIE standard o

38、bserver (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. Consequently, color differences are sel-dom if ever computed directly from differences in x, y, and Y.6.2 CIE 197

39、6 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 produce three opponent axesthat approximate the percepts of lightness-darkness, redness-greenness and yellown

40、ess-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! f QY! (4)b* 5 200 f QY! f QZ! (5)where:QX5 X/Xn!; QY5 Y/Yn!; QZ5 Z/Zn!andFQi! 5 Qj1/3if Qj. 6/29!3elseFQi! 5 841/108!Qi1 4/29 if Qj# 6/29!3.Here, i

41、 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 radiant power ofone of the CIE standard illuminants, for example, C, D65oranother phase of daylight, reflected into t

42、he 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-difference DE*abbetween two colorseach given in terms of L*, a*, b* is calculated as follows:DE*ab5 =DL*!21 Da*!21 Db*!

43、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 letterscapitalized) is recommended.6.2.2 The magnitude, DE*ab, gives no indication of thecharacter of the d

44、ifference 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 algebraic signs of the components DL*,Da*, and Db*:DL* 5 L*B2 L*S(7)Da* 5 a*B2 a*S(8)Db* 5 b*B2 b*S(9)where

45、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 DL*, D a*, and Db* have thefollowing approximate meanings (7):1DL* 5 lighter (10)2D L* 5 darker (11)1Da* 5 redder less green! (12)2Da* 5 greener less red! (13)1Db*

46、 5 yellow less blue! (14)2D b* 5 bluer less yellow! (15)6.2.4 For judging the direction of the color differencebetween two colors, it is useful to calculate their CIE 1976metric hue angles haband CIE 1976 metric chroma C*abasfollows:hab5 tan2 1Sb*a*D(16)C*ab5 =a*!21 b*!2(17)Differences in hue angle

47、habbetween the test specimen andreference can be correlated with differences in their visuallyperceived hue, except for very dark colors (8). Differences inchroma DC*a-b=(C*abbatchC*abstandard) can similarlybe correlated with differences in visually perceived chroma.6.2.5 For judging the relative co

48、ntributions of differences inlightness, chroma, and hue to the total color difference betweentwo colors, it is useful to calculate the CIE 1976 metric huedifference DH*abbetween them as follows:DH*ab5 =DE*ab!22 DL*!22 DC*ab!2(18)where DE*abis calculated as in 6.2.1 and DC*abis calculatedas in 6.2.4;

49、 then the equationDE*ab5 =DL*!21 DC*ab!21 DH*ab!2(19)contains terms showing the relative contributions of light-ness differenceD L*, chroma difference DC*ab, and hue differ-ence D H*abto the total color differenceD E*ab. This methodof computing a metric hue difference loses the informationabout the sign of the hue difference (positive or negative) andcan be unstable for pairs of colors near the neutral axis. Analternative method has been proposed (14) that corrects bothproblems:DH*ab5 s 2 C*ab,BC*ab,S a*Ba*S b*Bb*S!