ASTM D2244-2009a Standard Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Color Coordinates.pdf

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1、Designation: D 2244 09aStandard 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.INTRODUCTIONThis

3、 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 colo

4、r 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 th

5、e 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 pur

6、poses.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 sp

7、ecimens 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 terms of approximatelyuniform visual color perception in CIE

8、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-b

11、ility 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 MetamerismE 284 Terminology of AppearanceE 308 Practice for C

12、omputing 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 Evaluation2.2 Other Standards:DIN 6176 Farbmetrische, Bestimmung von Far

13、babstndenbei Krperfarben nach der DIN99-Formel41This 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 Aug. 1, 2009. Published August 2009. Originallyapprove

14、d in 1964. Last previous edition approved in 2009 as D 2244 09.2The 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

15、ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available from Beuth Verlag GmbH, 10772, Berlin, Germany, http:/www.beuth.de/.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO

16、Box C700, West Conshohocken, PA 19428-2959, United States.3. 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 (

17、such as a prism,grating 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 colorimetri

18、c spectrometer mayalso 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

19、common components, UV-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 digit

20、al simulations of the 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 toler

21、ance equation, na mathematical 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/fai

22、l value based on which 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 equationquantif

23、ies distance in a color 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 m

24、ade by use of aspectral 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. Col

25、or-difference unitsare 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 uniformvisua

26、lly. Each subsequent color 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 indiffere

27、nt color-scale systems 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 c

28、olor tolerances in one 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 coat

29、ings, plastics, textiles 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

30、is also not recommended 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*abuni

31、ts.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 specifiedtolerance from a standard. However, for control of color inproduction

32、, 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 threeinstrumentally determined components of the color difference.5.4 Selecti

33、on 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 D 1729. The three tolerance equa-tions given here have been tested extensively against such datafor

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

35、 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 visual judg-ments may not be obtained when the calculations are madewith oth

36、er illuminants. Use of a tolerance equation for otherthan daylight conditions will require visual confirmation of thelevel of metamerism in accordance with Practice D 4086.6. Description of Color-Difference and Color-ToleranceEquations6.1 CIE 1931 and 1964 Color SpacesThe daylight colorsof opaque sp

37、ecimens are represented by points in a spaceD 2244 09a2formed 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 observer (2 observer) or the 1964

38、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 1976 L* a* b* Uniform Color Space an

39、d 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 yellowness-blueness. It is produced by p

40、lottingin 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)whereQX5 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!3Here, i varies as X, Y, and Z.The tristimu

41、lus 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 the observers eye bythe perfect refl

42、ecting 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*!2(6)NOTE 1The color space defined a

43、bove 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 difference since it does not indicat

44、e 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 L*S, a*S, and b*Srefer to the refer

45、ence 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* 5 yellow less blue! (14)2D b* 5 bl

46、uer 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 to the followingpseudocode:(16)ifb* 5 0thenhab5 9090signa*!elsehab5 180 180/p! arctana*/b*! 90signb*!end if.Here sign is a f

47、unction that returns the sign of the argumentand arctan is the inverse tangent function returning angles inunits of radians. The units of habcalculated by the above aredegrees counter-clockwise from the positve a* axis.C*ab5 =a*!21 b*!2(17)Differences in hue angle habbetween the test specimen andref

48、erence can be correlated with differences in their visuallyperceived hue, except for very dark colors (8). Differences inchroma DC*ab=(C*abbatchC*abstandard) can similarly becorrelated with differences in visually perceived chroma.6.2.5 For judging the relative contributions of lightnessdifferences,

49、 chroma differences, and hue differences betweentwo colors, it is useful to calculate the CIE 1976 Metric HueDifference DH*abbetween the colors as follows:D H*ab5 s 2C*ab,BC*ab,S a*Ba*S b*Bb*S!#0.5(18)whereifa*Sb*B. a*Bb*S(19)thens 5 1elses 5 1end if.D 2244 09a3When DE*abis calculated as in 6.2.1 and DC*abis calculatedas in 6.2.4, thenDE*ab5 DL*!21 DC*!21 DH*!2#0.5(20)contains terms showing the relative contributions of light-ness differences DL*ab, chroma differences DC*ab, and huedifferences DH*ab.6.3 CMC Color