ASTM E1455-03(2010)
(Practice)Standard Practice for Obtaining Colorimetric Data from a Visual Display Unit Using Tristimulus Colorimeters
Standard Practice for Obtaining Colorimetric Data from a Visual Display Unit Using Tristimulus Colorimeters
SIGNIFICANCE AND USE
This practice may be applied when tristimulus colorimeters are used to measure the colors produced on self-luminous video display devices such as CRTs and flat-panel displays, including electroluminescent (EL) panels, field emission displays (FEDs), and back-lit liquid crystal displays (LCDs). This practice is not meant to be a complete description of a procedure to measure the color coordinates of a display. Rather, it provides a method for obtaining more accurate results when certain conditions are met. It may be used by any person engaged in the measurement of color on display devices who has access to the requisite equipment.
This practice defines a class of tristimulus colorimeters that may be said to be compatible with this practice.
SCOPE
1.1 This practice is intended as an aid for improving the accuracy of colorimetric measurements made with tristimulus colorimeters on visual display units, such as cathode ray tubes (CRTs) and self-luminous flat-panel displays. It explains a useful step in the analysis of colorimetric data that takes advantage of the fact that light from such displays consists of an additive mixture of three primary colored lights. However, it is not a complete specification of how such measurements should be made.
1.2 This practice is limited to display devices and colorimetric instruments that meet linearity criteria as defined in the practice. It is not concerned with effects that might cause measurement bias such as temporal or geometric differences between the instrument being optimized and the instrument used for reference.
1.3 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: E1455 − 03(Reapproved 2010)
Standard Practice for
Obtaining Colorimetric Data from a Visual Display Unit
Using Tristimulus Colorimeters
This standard is issued under the fixed designation E1455; 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.
INTRODUCTION
This practice provides directions for correcting the results obtained with tristimulus colorimeters
when measuring the tristimulus values or chromaticity coordinates of colored displays. Tristimulus
colorimeters approximate the CIE color matching functions x¯(λ), y¯(λ), z¯(λ) to make these measure-
ments. The errors generated in measuring colors on a display may be minimized using this practice.
1. Scope E1336 Test Method for Obtaining Colorimetric Data From a
Visual Display Unit by Spectroradiometry
1.1 This practice is intended as an aid for improving the
E1341 Practice for Obtaining Spectroradiometric Data from
accuracy of colorimetric measurements made with tristimulus
Radiant Sources for Colorimetry
colorimeters on visual display units, such as cathode ray tubes
2.2 ISO/CIE Standard:
(CRTs) and self-luminous flat-panel displays. It explains a
CIEStandardColorimetricObservers,ISO/CIE10527: 1991
useful step in the analysis of colorimetric data that takes
(E) (International Organization for Standardization,
advantage of the fact that light from such displays consists of
Geneva, 1991)
an additive mixture of three primary colored lights. However,
it is not a complete specification of how such measurements
3. Terminology
should be made.
3.1 Definitions—Unless otherwise stated, definitions of ap-
1.2 This practice is limited to display devices and colori-
pearance terms in Terminology E284 are applicable to this
metric instruments that meet linearity criteria as defined in the
practice.
practice. It is not concerned with effects that might cause
3.2 Definitions of Terms Specific to This Standard:
measurement bias such as temporal or geometric differences
3.2.1 calibration, n—in reference to a tristimulus
between the instrument being optimized and the instrument
colorimeter, the process performed outside of this practice to
used for reference.
adjust the tristimulus colorimeter to provide the best possible
1.3 This standard does not purport to address all of the
results for average or predefined conditions.
safety concerns, if any, associated with its use. It is the
3.2.2 optimization, n—in reference to a tristimulus
responsibility of the user of this standard to establish appro-
colorimeter, the process performed pursuant to this practice to
priate safety and health practices and determine the applica-
adjust the tristimulus colorimeter or to interpret its readings to
bility of regulatory limitations prior to use.
provide better results when applied to a particular display
2. Referenced Documents device.
3.2.3 compatible, adj—in reference to a tristimulus
2.1 ASTM Standards:
colorimeter, one so designed as to automate the procedure
E284 Terminology of Appearance
described in this practice.
1 4. Summary of Practice
This practice is under the jurisdiction of ASTM Committee E12 on Color and
Appearance and is the direct responsibility of Subcommittee E12.06 on Display,
4.1 Tristimulus colorimeters comprised of three or four
Imaging and Imaging Colorimetry.
detector channels are, in general, not amenable to accurate
Current edition approved March 1, 2010. Published March 2010. Originally
approved in 1992. Last previous edition approved in 2003 as E1455 – 03. DOI:
10.1520/E1455-03R10.
2 3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Currently available through the U.S. National Committee of the CIE, c/o Mr.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Thomas M. Lemons, TLA-Lighting Consultants, Inc., 7 Pond Street, Salem, MA
Standards volume information, refer to the standard’s Document Summary page on 01970-4819. Also included in ASTM Standards on Color and Appearance, Fifth
the ASTM website. Edition, 1996.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1455 − 03 (2010)
calibration that holds for all manner of usage with different 10527 and the CIE in its publication No. 15.2 (1). For light
illuminated devices and objects. This is because the spectral with a color stimulus function Φ(λ),
responsivities of their detector channels do not exactly match 830 nm
the defined Commission Internationale de L’Éclairage (CIE) X 5 k Φ λ x¯ λ dλ (1)
* ~ ! ~ !
360 nm
x¯(λ), y¯(λ), z¯(λ) functions. Factory or subsequent calibration
reflects judgments and compromises that may not be readily 830 nm
apparent. Nevertheless, this practice provides guidance on how Y 5 k Φ λ y¯ λ dλ
* ~ ! ~ !
360 nm
such a tristimulus colorimeter may be optimized for use with a
particular video display device, providing better accuracy with 830 nm
that device than its more general calibration provides. An
Z 5 k * Φ~λ!z¯~λ!dλ
360 nm
optimization matrix transforms the instrumental (measured)
CIE X, Y, Z values into adjusted X, Y, Z values that are closer
where:
to the ideal. This matrix is determined by reference to a
k is 683 lm/W for emissive devices, such as displays, and x¯(λ),
colorimeter with higher intrinsic accuracy. The method derives
y¯(λ), z¯(λ) are color-matching functions. While the standard
from the fact that the color stimulus functions from display definition of X, Y, Z requires the use of the CIE 1931 2°
devices are linear combinations of three primary functions and color-matching functions, the mathematics described in this
practice would also be applicable to any other set of color-
are not entirely arbitrary.
matching functions, such as the CIE 1964 10° functions.
6.1.3 In practice, color measurement instruments compute
5. Significance and Use
X, Y, Z by the summation of the signals as measured through
5.1 This practice may be applied when tristimulus colorim-
the various filters, each signal being multiplied by an appro-
eters are used to measure the colors produced on self-luminous
priate calibration factor. In matrix notation:
video display devices such as CRTs and flat-panel displays,
X C C C . C F
m X1 X2 X3 Xf 1
including electroluminescent (EL) panels, field emission dis-
Y C C C . C F
5 (2)
m Y1 Y2 Y3 Yf 2
F G F G
plays (FEDs), and back-lit liquid crystal displays (LCDs). This
Z C C C . C F
m Z1 Z2 Z3 Zf 3
practice is not meant to be a complete description of a
¡
3 4
proceduretomeasurethecolorcoordinatesofadisplay.Rather,
F
f
it provides a method for obtaining more accurate results when
certain conditions are met. It may be used by any person where:
engaged in the measurement of color on display devices who
F , F , F , through F are the electrical signals from the f
1 2 3 f
has access to the requisite equipment. filtered detectors and the C are calibration coefficients. X ,
ij m
Y , Z have subscripts to indicate that they are measured
m m
5.2 This practice defines a class of tristimulus colorimeters
values rather than ideal ones.
that may be said to be compatible with this practice.
6.1.4 In this practice, we presume that the color measuring
instrument is linear: that each signal F is strictly proportional
a
6. Background of Practice
to the received optical power, that any zero-offset (background
in darkness) is removed, that the proportionality for signal F
a
6.1 Colorimetry:
is not affected by the value of signal F , and in the case of
b
6.1.1 Color measurement instruments consist, in general, of
closely packed detectors (such as charge-coupled device
means to measure radiometric power as transmitted through a
(CCD) detector elements) no signal F spills over and affects
a
number of bandpass filters. Most commonly, electrical devices
signal F as it approaches saturation. These presumptions are
b
are used to measure the filtered light. They may be used with
amenable to experimental verification using methods beyond
different filters in succession, or multiple devices may be used
the scope of this practice (2).
concurrently. In instruments called spectroradiometers, the
6.1.5 The values of the matrix elements C may be deter-
ij
radiometric power is measured through a large number (typi-
mined using criteria that depends on the design and intended
cally 30 to 500) of narrowband filters. (Practice E1341 de-
application of the instrument. The full extent of this subject is
scribeshowamonochromatororpolychromator(spectrograph)
beyond the scope of this practice. However, in general, for
may be employed to filter and measure light in separate bands
spectroradiometers (f ≈ 30 to 500), C reflects the tabulated
Xj
on the order of 1-nm wide.) In instruments called tristimulus
value of x¯(λ) near the center wavelength of Filter j as well as
colorimeters, the radiometric power is measured through three
thespectralresponsivityofthecorrespondingdetectorchannel.
or four wideband filters. These filters may be constructed from
(Likewise, C and C reflect y¯(λ) and z¯(λ), respectively.) For
Yj Zj
dispersive elements (prisms and gratings) or from materials
tristimulus colorimeters, the choice of C is discussed further,
ij
with selective spectral transmission or reflection. The latter below. As a general matter, the instrument designer should
may be either uniform or comprised of different patches, in a choose passbands and matrix elements that balance accuracy,
mosaic pattern, that provide the desired overall effect. sensitivity, and other design requirements.
6.1.2 No matter how many filters are used, or in what
manner, the goal of the measurement process is to determine 4
The boldface numbers in parentheses refer to the list of references at the end of
tristimulus values X, Y, Z, as defined by ISO in its Standard this standard.
E1455 − 03 (2010)
6.1.6 Tristimulus colorimeters are generally designed with does not represent that any particular display device will act as
filters that are intended to match the spectral responsivities of predicted by Eq 6, though those within the mentioned classes
their detector channels to the CIE x¯(λ), y¯(λ), z¯(λ) functions. For of devices might do so. The procedure for experimental
such an instrument, verification of this property for a specific display device is
beyond the scope of this practice (3).
X C 00 F
m X1 1
Y 0 C 0 F 6.3 Colorimetric Measurement of Displays:
5 (3)
m Y2 2
F G F GF G
6.3.1 Each of the primary color stimulus functions Φ (λ),
Z 00 C F
r
m Z3 3
Φ (λ), Φ (λ)stimulatesresponsesinthe fdetectorchannelsthat
g b
where:
may be represented by a vectorF (that is,F ,F ,F ). Given
r g b
the non-zero C matrix elements represent adjustable gains of
ij
their construction, these vectors are linearly independent.
the detector channels. However, the x¯(λ) function has two
(None of the three can be expressed as a linear combination of
distinct lobes. This may be dealt with by splitting x¯(λ) into
the other two.) While F is an element of an f-dimensional
x¯ (λ) and x¯ (λ), each with a separate filter (F and F ,
short long 1 2
vector space, it is clear that only a three-dimensional subspace
respectively). For such an instrument,
is spanned by the F’s of all possible color stimulus functions
X C C 00 F following Eq 6. Further, the mapping of F into (X , Y , Z )
m X1 X2 1 m m m
space by Eq 2 remains three dimensional. In other words, there
Y 00 C 0 F
5 (4)
m Y3 2
F G F G
is a one-to-one mapping of the vector (a, b, c) onto (X, Y, Z)by
Z 000 C F
m Z4 3
3 4
application of Eq 1; and, for a particular instrument with a
F
fixed calibration matrixC, there is also a one-to-one mapping
Alternatively, the z¯(λ) function may serve the role of x¯ (λ)
short
of the vector (a, b, c) onto (X , Y , Z ). From this we deduce
m m m
since they have a similar shape,
that a matrixR exists that can be used to translate (X , Y , Z )
m m m
values into actual (X, Y, Z) values.
X C 0 C F
m X1 X3 1
6.3.2 A colorimeter that takes advantage of this fact must
Y 0 C 0 F
5 (5)
m Y2 2
F G F GF G
provide means for implementing the matrix R. That is, all f
Z 00 C F
m Z3 3
filtered detector signals should contribute linearly toward the
In all of these cases, it is difficult to realize an exact match
computation of each output, X , Y , Z , instead of using
m m m
between the CIE color-matching functions and the actual
different detectors for each output. This idea was reported as
spectral responsivities of the corresponding detector channels.
long ago as 1973 by Wagner (4), and it has been expanded
Thismeansthatnochoiceof C willprovideperfectcalibration
ij
upon and rediscovered by others since then (5-10).
forallapplicationsoftheinstrument.Thecriteriaforsettingthe
6.3.3 On the basis of this property, a tristimulus colorimeter
C might not be well documented for a particular instrument.
ij
can be optimized for use on a self-luminous display by the
6.1.7 It is generally believed that spectroradiometers, with
proper derivation of a matrixR for that display.We proceed on
their many detector channels, may be calibrated to yield
theassumptionsthatthecomponentsaresufficientlystable,and
superior measurements of X, Y, Z for diverse applications.
that similarly built displays have similar enough spectral
Nevertheless, the relative simplicity of tristimulus colorimeters
primaries to make a derivation of R worthwhile. However,
and their commensurately lower cost have made them popular
these assumptions should be quantified before accuracy claims
where the highest accuracy is not required.
are made in any specific situation.
6.3.4 On the basis of this property, a tristimulus colorimeter
6.2 Self-Luminous Displays:
designed for use with displays need not produce signalsF that
6.2.1 A self-luminous display, such as a CRT, an electrolu-
are close to CIE tristimulus values. Signal/noise may be
minescent (EL) panel, a field emission display (FED), or a
improved by matching the spectral responsivities of the filtered
back-lit liquid crystal display (LCD) generates colored light by
detectors to the emission spectra of the primary colors. In such
the proportional superposition (addition) of primary colored
designs, it is especially important to use a matrix R that is
lights Φ (λ), Φ (λ), Φ (λ). The subscripts represent red, green,
r g b
specific to the particular Φ (λ), Φ (λ), Φ (λ).
r g b
and blue, the primary colors of an additive set. An arbitrarily
colored patch on the visual display has one and only one color
7. Optimization
stimulus function Φ(λ),
7.1 General:
Φ λ 5 aΦ λ 1bΦ λ 1cΦ
...
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