1、Designation: E 313 05Standard Practice forCalculating Yellowness and Whiteness Indices fromInstrumentally Measured Color Coordinates1This standard is issued under the fixed designation E 313; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r
2、evision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This practice p
3、rovides numbers that correlate withvisual ratings of yellowness or whiteness of white and near-white or colorless object-color specimens, viewed in daylightby an observer with normal color vision. White textiles, paints,and plastics are a few of the materials that can be described bythe indices of y
4、ellowness or whiteness calculated by thispractice.1.2 For a complete analysis of object colors, by a specifiedobserver and under a specified illuminant, use of three param-eters is required. For near-white specimens, however, it is oftenuseful to calculate single-number scales of yellowness orwhiten
5、ess. This practice provides recommended equations forsuch scales and discusses their derivations and uses, and limitsto their applicability (see also Ref (1)2).1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This standar
6、d 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-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM
7、 Standards:3D 1535 Practice for Specifying Color by the Munsell Sys-temD 1729 Practice for Visual Appraisal of Colors and ColorDifferences of Diffusely-Illuminated Opaque MaterialsD 1925 Test Method for Yellowness Index of Plastics4E 284 Terminology of AppearanceE 308 Practice for Computing the Colo
8、rs of Objects byUsing the CIE SystemE 805 Practice for Identification of Instrumental Methods ofColor or Color-Difference Measurement of MaterialsE 991 Practice for Color Measurement of FluorescentSpecimens3E 1164 Practice for Obtaining Spectrophotometric Data forObject-Color EvaluationE 1247 Practi
9、ce for Detecting Fluorescence in Object-ColorSpecimens by SpectrophotometryE 1331 Test Method for Reflectance Factor and Color bySpectrophotometry Using Hemispherical GeometryE 1345 Practice for Reducing the Effect of Variability ofColor Measurement by Use of Multiple Measurements3E 1347 Test Method
10、 for Color and Color-Difference Mea-surement by Tristimulus (Filter) Colorimetry3E 1348 Test Method for Transmittance and Color by Spec-trophotometry Using Hemispherical GeometryE 1349 Test Method for Reflectance Factor and Color bySpectrophotometry Using Bidirectional Geometry3E 1360 Practice for S
11、pecifying Color by Using the OpticalSociety of America Uniform Color Scales SystemE 1499 Guide for Selection, Evaluation, and Training ofObserversE 1541 Practice for Specifying and Matching Color Usingthe Colorcurve System33. Terminology3.1 Terms and definitions in Terminology E 284 are appli-cable
12、to this practice.3.2 Definitions:3.2.1 perfect reflecting diffuser, nideal reflecting surfacethat neither absorbs nor transmits light, but reflects diffusely,with the radiance of the reflecting surface being the same for allreflecting angles, regardless of the angular distribution of theincident lig
13、ht.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 Oct. 1, 2005. Published October 2005. Originallyapproved in 1967. Last previous edition approved i
14、n 2000 as E 313 00.2The boldface numbers in parentheses refer to the list of references at the end ofthis practice.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 t
15、he standards Document Summary page onthe ASTM website.4Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.2 whiteness, nthe attribute of color perception bywhich an object color is judged to approach the preferredwhite.3.2
16、.3 whiteness index, WI, na number, computed by agiven procedure from colorimetric data, that indicates thedegree of departure of an object color from that of a preferredwhite.3.2.4 yellowness, nthe attribute of color perception bywhich an object color is judged to depart from colorless or apreferred
17、 white toward yellow.3.2.5 yellowness index, YI, na number, computed by agiven procedure from colorimetric or spectrophotometric data,that indicates the degree of departure of an object color fromcolorless or from a preferred white, toward yellow.3.2.5.1 DiscussionNegative values of YI denote depart
18、uretoward blue.3.3 Definitions of Terms Specific to This Practice:3.3.1 near white, na color having a Munsell value greaterthan 8.3 (luminous reflectance factor Y = 63) and Munsellchroma no greater than 0.5 for B hues, 0.8 for Y hues, and 0.3for all other hues.3.3.2 preferred white, ncolor of a whit
19、e standard used asthe basis for calculating indices of whiteness or yellowness asthe departure of the color of the specimen from that of thepreferred white; in this practice, the perfect reflecting diffuser.4. Summary of Practice4.1 The calculations described in this practice assume thatspecimens ha
20、ve been measured according to Practices E 1164and E 308 and one of the Test Methods E 1331, E 1347,E 1348, or E 1349, depending on the type of specimen andmeasuring instrument used (see also Practice E 805).4.2 This practice takes as a starting point for the calculationsCIE tristimulus values X, Y,
21、and Z for one of the CIE standardobservers and one of the CIE standard or recommendedilluminants of daylight quality. Such tristimulus values areavailable by use of modern color measuring instruments.4.3 Equations for the preferred methods of calculating YIand WI are described in Sections 6 and 7, r
22、espectively.Equations for calculating other quantities used as indices ofyellowness or whiteness are given in Appendix X1 andAppendix X2, respectively.5. Significance and Use5.1 This practice should be used only to compare specimensof the same material and same general appearance. Forexample, a seri
23、es of specimens to be compared should havegenerally similar gloss, texture, and (if not opaque) thickness,and translucency.5.2 For yellowness measurement, this practice is limited tospecimens having dominant wavelength in the range 570 to580 nm, or Munsell hue approximately 2.5GY to 2.5 Y. Forwhiten
24、ess measurement, this practice is limited to specimenshaving Munsell value greater than 8.3 (CIE Y greater than 65)and Munsell chroma no greater than 0.5 for B hues, 0.8 for Yhues, and 0.3 for all other hues (see 3.3.1).5.3 The combination of measurement and calculation lead-ing to indices of yellow
25、ness or whiteness is a psychophysicalprocess, that is, the procedures specified are designed toprovide numbers correlating with visual estimates made underspecified typical observing conditions. Because visual observ-ing conditions can vary widely, users should compare calcu-lated indices with visua
26、l estimates to ensure applicability.Some standards addressing the visual estimation of color andcolor difference are Practices D 1535, D 1729, E 1360, andE 1541, and Guide E 1499.5.4 This practice does not cover the preparation of speci-mens, a procedure that may affect significantly the quantitiesm
27、easured. In general, specimens should be prepared andpresented for measurement in the manner that is standard forthe test being performed. Select enough specimens or specimenareas to provide an average result that is representative of eachsample to be tested. See Practice E 1345.6. Yellowness Index6
28、.1 BackgroundThe currently recommended equation forthe calculation of yellowness index is derived from an equationdue to Hunter (2) in 1942: YI =(AB)/G, where A, B, and Gare, respectively, amber or red, blue, and green colorimeterreadings. Another version, used in the 1940s to 1960s fortransparent p
29、lastics (3, 4), was based on transmittances near theends of the visible wavelength region: YI = 100(T680 T420)/T560(with a factor of 100 introduced to give values of YInear unity). This equation failed to account correctly fordifferences in the spectral transmittance curves of such plastics,especial
30、ly after the adoption of ultraviolet light absorbers toimprove weathering, and was soon abandoned. When, in 1957,ASTM solicited new equations for calculating yellownessindices, Hunters equation was converted (5) into CIE tristimu-lus value form by using Hunters approximate relations be-tween colorim
31、eter readings and those tristimulus values; theresulting equation, YI = 100(1.28X 1.06Z)/Y, was adoptedfor use in Test Method D 1925 in 1962.6.1.1 In the original form of Test Method E 313, an alter-native equation was recommended for a yellowness index. Interms of colorimeter readings, it was YI =
32、100(1 B/G). Itsderivation assumed that, because of the limitation of theconcept to yellow (or blue) colors, it was not necessary to takeaccount of variations in the amber or red colorimeter reading A.This equation is no longer recommended.6.2 Significant Digits and PrecisionThe coefficients ofTest M
33、ethod D 1925 equation were rounded to the number ofdigits shown, commensurate with the precision of then-existingcolor measurement instrumentation. It was not intended thatmore significance should be attributed to values of YI than thatimplicit in this number of digits. As instrumentation wasimprove
34、d, however, it was found that some instruments unex-pectedly gave nonzero values of YI for clear air or the perfectreflecting diffuser. One suggested (1), p. 205) remedy for thispresumed failure of the equation was to increase the number ofdigits in the numerical coefficients from two to ten after t
35、hedecimal point, despite the obvious lack of significance of mostof these digits. With modern instrumentation, it is believed thattwo digits added to the coefficients in the original Test MethodD 1925 equation suffice to bring the nonzero value of YI below0.0005 on average. The new coefficients are
36、given to thisprecision in 6.3.E3130526.3 Derivation of EquationsSeveral sets of coefficientsare involved in the derivation of the final equations recom-mended for calculating yellowness indices. With them evalu-ated, it is possible to derive highly precise equations for boththe CIE 1931 standard obs
37、erver and the 1964 supplementarystandard observer, in combination with either CIE standardilluminant C or D65. The results are given in Table 1.6.3.1 The first set of coefficients required, consists of thetristimulus values Xn, Yn, and Znof the perfect reflectingdiffuser (or clear air) for the above
38、 observer-illuminant com-binations. These are established by the CIE, and for the presentderivation were taken from the tables of tristimulus weightingfactors in Practice E 308.6.3.2 From these “white point” values, it is possible tocalculate the coefficients in Hunters equation relating tristimu-lu
39、s value X and colorimeter readings A and B: X=Xn(FAA+ FBB), thus improving on the approximation FA= 0.8 andFB= 0.2 originally used.6.3.3 Finally, the coefficients in revisedTest Method D 1925equations for YI can be calculated, rounded, and adjusted in thelast retained significant digit to minimize t
40、he residual error inthe white point values. These coefficients are given in Table 1as CXand CZin the recommended equation for yellownessindex:YI 5 100CXX 2 CZZ!/Y (1)The tabulation of the residual white point error completes thetable.7. Whiteness Index7.1 BackgroundThe earliest equation for whitenes
41、s indexWI appears to be due to MacAdam (6) and related WI toexcitation purity. This and other equations utilizing the purityhave largely been abandoned. Judd (7) appears to have been thefirst to recognize that a whiteness index should incorporate twoterms, one based on the lightness of the specimen
42、relative tothat of a preferred white, and the other describing the differ-ence in chromaticity between the specimen and that preferredwhite. Much debate has arisen over the years as to the natureof the preferred white, but at the present time the perfectreflecting diffuser is almost always adopted a
43、s that reference.7.1.1 In the original form of Test Method E 313, theequation for WI was based on the above premise and the use ofcolorimeter readings G and B only. It was found that thechromaticity factor GB required three to four times theweighting of the lightness factor G. Hence the equation was
44、written WI=G4(GB)=4B 3G. This equation is nolonger recommended.7.2 CIE EquationsThe equations for whiteness recom-mended in this practice were derived and published (8) by theCIE. Two equations are given, one for the whiteness index WIand another for a tint index T. Their coefficients are given inTa
45、ble 2. The CIE gave coefficients for both standard observersand Ill. D65; those for the 1931 observer and Ill. C were takenfrom the American Association of Textile Chemists and Col-orists (AATCC) method for WI (9); and those for the 1964observer and Ill. C and Ill. D50were estimated by Subcommit-tee
46、 E12.04. Those for Ill. C and Ill. D50and both observers areunofficial and should be used for in-house comparisons only.7.2.1 Equation for Whiteness Index WI:WI 5 Y 1 WI, x! xn2 x! 1 WI, y! yn2 y! (2)where:Y, x, y = the luminance factor and the chroma-ticity coordinates of the specimen,xnand yn= the
47、 chromaticity coordinates for theCIE standard illuminant and sourceused, andWI, x and WI, y = numerical coefficients.Values for all these except those measured for the specimenare given in Table 2.7.2.2 Equation for Tint Index T:T 5 T, x xn2 x! 2 T, y yn2 y! (3)where the symbols have meanings analog
48、ous to those in7.2.1.7.3 Notes and Restrictions to the CIE EquationsThe CIEnotes the following regarding the use of equations for WI andT:7.3.1 The application of the equations is restricted to speci-mens that are called “white” commercially, that are similar incolor and fluorescence, and that are m
49、easured on the sameinstrument at about the same time. Under these conditions theiruse should give relative, but not absolute, evaluations ofwhiteness that are adequate for commercial use.7.3.2 The higher the value of WI, the greater is the indicatedwhiteness. The more positive the value of T, the greater is theindicated greenish tint of the specimen; the more negative thevalue of T, the greater is its reddish tint. Lines of equal T areapproximately parallel to the line of dominant wavelength 466nm. For the perfect reflecting diffuser, WI = 100 and T
