ASTM E308-12
(Practice)Standard Practice for Computing the Colors of Objects by Using the CIE System
Standard Practice for Computing the Colors of Objects by Using the CIE System
SIGNIFICANCE AND USE
5.1 The CIE colorimetric systems provide numerical specifications that are meant to indicate whether or not pairs of color stimuli match when viewed by a CIE standard observer. The CIE color systems are not intended to provide visually uniform scales of color difference or to describe visually perceived color appearances.
5.2 This practice provides for the calculation of tristimulus values X, Y, Z and chromaticity coordinates x, y that can be used directly for psychophysical color stimulus specification or that can be transformed to nearly visually uniform color scales, such as CIELAB and CIELUV. Uniform color scales are preferred for research, production control, color-difference calculation, color specification, and setting color tolerances. The appearance of a material or an object is not completely specified by the numerical evaluation of its psychophysical color, because appearance can be influenced by other properties such as gloss or texture.
SCOPE
1.1 This practice provides the values and practical computation procedures needed to obtain CIE tristimulus values from spectral reflectance, transmittance, or radiance data for object-color specimens.
1.2 Procedures and tables of standard values are given for computing from spectral measurements the CIE tristimulus values X, Y, Z, and chromaticity coordinates x, y for the CIE 1931 standard observer and X10, Y10, Z10 and x10. y10 for the CIE 1964 supplementary standard observer.
1.3 Standard values are included for the spectral power of six CIE standard illuminants and three CIE recommended fluorescent illuminants.
1.4 Procedures are included for cases in which data are available only in more limited wavelength ranges than those recommended, or for a measurement interval wider than that recommended by the CIE. This practice is applicable to spectral data obtained in accordance with Practice E1164 with 1-, 5-, 10-, or 20-nm measurement interval.
1.5 Procedures are included for cases in which the spectral data are, and those in which they are not, corrected for bandpass dependence. For the uncorrected cases, it is assumed that the spectral bandpass of the instrument used to obtain the data was approximately equal to the measurement interval and was triangular in shape. These choices are believed to correspond to the most widely used industrial practice.
1.6 This practice includes procedures for conversion of results to color spaces that are part of the CIE system, such as CIELAB and CIELUV (3). Equations for calculating color differences in these and other systems are given in Practice D2244.
1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E308 − 12
StandardPractice for
1
Computing the Colors of Objects by Using the CIE System
This standard is issued under the fixed designation E308; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript 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.
INTRODUCTION
Standardtables(Tables1–4)ofcolormatchingfunctionsandilluminantspectralpowerdistributions
have since 1931 been defined by the CIE, but the CIE has eschewed the role of preparing tables of
tristimulus weighting factors for the convenient calculation of tristimulus values. There have
subsequently appeared numerous compilations of tristimulus weighting factors in the literature with
disparity of data resulting from, for example, different selections of wavelength intervals and methods
2
of truncating abbreviated wavelength ranges. In 1970, Foster et al. (1) proposed conventions to
standardize these two features, and Stearns (2) published a more complete set of tables. Stearns’ work
andlaterpublicationssuchasthe1985revisionofE308havegreatlyreducedthesubstantialvariations
in methods for tristimulus computation that existed several decades ago.
The disparities among earlier tables were largely caused by the introduction of computations based
on 20-nm wavelength intervals. With the increasing precision of modern instruments, there is a
likelihood of a need for tables for narrower wavelength intervals. Stearns’ tables, based on a 10-nm
interval, did not allow the derivation of consistent tables with wavelength intervals less than 10 nm.
The 1-nm table must be designated the basic table if others with greater wavelength intervals are to
have the same white point, and this was the reason for the 1985 revision of E308, resulting in tables
that are included in the present revision as Tables 5.
The 1994 revision was made in order to introduce to the user a method of reducing the dependence
of the computed tristimulus values on the bandpass of the measuring instrument, using methods that
are detailed in this practice.
1. Scope 1931 standard observer and X ,Y ,Z and x .y for the
10 10 10 10 10
CIE 1964 supplementary standard observer.
1.1 This practice provides the values and practical compu-
tation procedures needed to obtain CIE tristimulus values from 1.3 Standard values are included for the spectral power of
spectral reflectance, transmittance, or radiance data for object- six CIE standard illuminants and three CIE recommended
color specimens. fluorescent illuminants.
1.2 Procedures and tables of standard values are given for 1.4 Procedures are included for cases in which data are
computing from spectral measurements the CIE tristimulus available only in more limited wavelength ranges than those
values X, Y, Z, and chromaticity coordinates x, y for the CIE recommended, or for a measurement interval wider than that
recommended by the CIE. This practice is applicable to
spectral data obtained in accordance with Practice E1164 with
1
This practice is under the jurisdiction of ASTM Committee E12 on Color and
1-, 5-, 10-, or 20-nm measurement interval.
Appearance and is the direct responsibility of Subcommittee E12.04 on Color and
1.5 Procedures are included for cases in which the spectral
Appearance Analysis.
Current edition approved July 1, 2012. Published December 2012. Originally
data are, and those in which they are not, corrected for
approved in 1966. Last previous edition approved in 2008 as E308 – 08. DOI:
bandpass dependence. For the uncorrected cases, it is assumed
10.1520/E0308-12.
2 that the spectral bandpass of the instrument used to obtain the
The boldface numbers in parentheses refer to the list of references at the end of
this practice. data was approximately equal to the measurement interval and
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
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E308 − 12
was triangular in shape. These choices are believed to corre- 3.2.2 bandwidth, n—the width of a passband at its half-peak
spond to the most widely used industrial practice. transmittance.
1.6 This practice includes procedures for conversion of
3.2.3 chromaticity, n—the color quality of a color stimulus
results to color spaces that are part of the CIE system, such as
definable by its chromaticity coordinates.
CIELAB and CIELUV (3). Equations for calculating color
3.2.4 chromaticity coordinates, n—the ratio of each of the
differences in these and other systems are given in Practice
tristimulus values of a psychophysical color (see se
...
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
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 version
of the standard as published by ASTM is to be considered the official document.
Designation: E308 − 08 E308 − 12
Standard Practice for
1
Computing the Colors of Objects by Using the CIE System
This standard is issued under the fixed designation E308; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript 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.
INTRODUCTION
Standard tables ((TablesTables 1-4) 1–4) of color matching functions and illuminant spectral power
distributions have since 1931 been defined by the CIE, but the CIE has eschewed the role of preparing
tables of tristimulus weighting factors for the convenient calculation of tristimulus values. There have
subsequently appeared numerous compilations of tristimulus weighting factors in the literature with
disparity of data resulting from, for example, different selections of wavelength intervals and methods
2
of truncating abbreviated wavelength ranges. In 1970, Foster et al. (1) proposed conventions to
standardize these two features, and Stearns (2) published a more complete set of tables. Stearns’ work
and later publications such as the 1985 revision of E308 have greatly reduced the substantial variations
in methods for tristimulus computation that existed several decades ago.
The disparities among earlier tables were largely caused by the introduction of computations based
on 20-nm wavelength intervals. With the increasing precision of modern instruments, there is a
likelihood of a need for tables for narrower wavelength intervals. Stearns’ tables, based on a 10-nm
interval, did not allow the derivation of consistent tables with wavelength intervals less than 10 nm.
The 1-nm table must be designated the basic table if others with greater wavelength intervals are to
have the same white point, and this was the reason for the 1985 revision of E308, resulting in tables
that are included in the present revision as Tables 5.
The 1994 revision was made in order to introduce to the user a method of reducing the dependence
of the computed tristimulus values on the bandpass of the measuring instrument, using methods that
are detailed in this practice. These changes, however, lead to tables (Tables 6 in this practice) that are
substantially different from the Tables 5 that have been in use since 1985. There is accordingly a
danger, if the new tables are introduced but not universally adopted, that there may again be, perhaps
for several decades, a significant disparity among the tables of tristimulus weighting factors commonly
used. It is highly desirable that this should be avoided.
1. Scope
1.1 This practice provides the values and practical computation procedures needed to obtain CIE tristimulus values from
spectral reflectance, transmittance, or radiance data for object-color specimens.
1.2 Procedures and tables of standard values are given for computing from spectral measurements the CIE tristimulus values
X, Y, Z, and chromaticity coordinates x, y for the CIE 1931 standard observer and X , Y , Z and x . y for the CIE 1964
10 10 10 10 10
supplementary standard observer.
1.3 Standard values are included for the spectral power of six CIE standard illuminants and three CIE recommended fluorescent
illuminants.
1.4 Procedures are included for cases in which data are available only in more limited wavelength ranges than those
recommended, or for a measurement interval wider than that recommended by the CIE. This practice is applicable to spectral data
obtained in accordance with Practice E1164 with 1-, 5-, 10-, or 20-nm measurement interval.
1
This practice is under the jurisdiction of ASTM Committee E12 on Color and Appearance and is the direct responsibility of Subcommittee E12.04 on Color and
Appearance Analysis.
Current edition approved Dec. 1, 2008July 1, 2012. Published January 2009December 2012. Originally approved in 1966. Last previous edition approved in 20062008
as E308 – 06.E308 – 08. DOI: 10.1520/E0308-08.10.1520/E0308-12.
2
The boldface numbers in parentheses refer to the list of references at the end of this practice.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
---------------------- Page: 1 ----------------------
E308 − 12
TABLE 1 Spectral Tristimulus Values (Color-Matching Functions) x¯,y¯,z¯ of the CIE 1931 Standard (2°) Observer, at 5 nm
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