ASTM E1682-08(2018)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E1682 − 08 (Reapproved 2018)
Standard Guide for
Modeling the Colorimetric Properties of a CRT-Type Visual
Display Unit
This standard is issued under the fixed designation E1682; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
This guide provides directions and mathematical models for deriving the relationship between
digital settings in a computer-controlled visual display unit and the resulting photometric and
colorimetricoutputofthedisplayunit.Theaccuratedeterminationofthisrelationshipiscriticaltothe
goal of accurate, device-independent color simulation on a visual display unit.
1. Scope 2. Referenced Documents
1.1 This guide is intended for use in establishing the 2.1 ASTM Standards:
operating characteristics of a visual display unit (VDU), such E284Terminology of Appearance
as a cathode ray tube (CRT). Those characteristics define the E1336Test Method for Obtaining Colorimetric Data From a
relationship between the digital information supplied by a Visual Display Unit by Spectroradiometry
computer, which defines an image, and the resulting spectral E1455Practice for Obtaining Colorimetric Data from a
radiant exitance and CIE tristimulus values. The mathematical Visual Display Unit Using Tristimulus Colorimeters
descriptionofthisrelationshipcanbeusedtoprovideanearby
3. Terminology
device-independentmodelfortheaccuratedisplayofcolorand
colored images on the VDU. The CIE tristimulus values
3.1 Definitions of appearance terms in Terminology E284
referred to here are those calculated from the CIE 1931 2°
are applicable to this guide.
standard colorimetric (photopic) observer.
3.2 Acronyms:
1.2 This standard does not purport to address all of the
3.2.1 CRT, n—anabbreviationforthetermcathoderaytube,
safety concerns, if any, associated with its use. It is the
a device for projecting a stream of electrons onto a phosphor-
responsibility of the user of this standard to establish appro-
coated screen in such a way as to display characters and
priate safety, health, and environmental practices and deter-
graphics.
mine the applicability of regulatory limitations prior to use.
3.2.2 DAC, n—anabbreviationforthetermdigitaltoanalog
1.3 This international standard was developed in accor-
converter, a device for accepting a digital computer bit pattern
dance with internationally recognized principles on standard-
and translating it into an analog voltage of a prescribed value.
ization established in the Decision on Principles for the
3.2.3 LUT, n—an abbreviation for the term look up table, a
Development of International Standards, Guides and Recom-
process in which input and output values are mapped in an
mendations issued by the World Trade Organization Technical
n-dimensional table such that, for a given input value, the
Barriers to Trade (TBT) Committee.
appropriate output value is “looked-up” from the table.
This guide is under the jurisdiction of ASTM Committee E12 on Color and
Appearance and is the direct responsibility of Subcommittee E12.06 on Display,
Imaging and Imaging Colorimetry. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2018. Published May 2018. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1995. Last previous edition approved in 2013 as E1682–08 (2013). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/E1682-08R18. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1682 − 08 (2018)
3.2.4 VDU, n—an abbreviation for the term visual display Sixth, there is no ambient glare (flare) from the screen into the
unit, a device interfaced to a computer for displaying text and observer’s eyes. Seventh, the refresh rate of the image is rapid
graphics. enough to produce temporal fusion (no noticeable flicker) for
3.2.4.1 Discussion—A CRT is one type of VDU. the normal observer. Eighth, the pixel pitch is fine enough to
produce spatial fusion for the normal observer. Each of the
4. Summary of Guide eight basic assumptions should be tested and either verified,
noted, or corrected before deriving a characteristic model.
4.1 EverycolorstimulusgeneratedonaVDUisrealizedby
6.1.1 Assumption1,independenceoftheprimaries,istested
the linear (additive) superposition of the spectral power distri-
by measuring the radiometric output at several levels, as
butionofthreeprimaries.TestMethodE1336describeshowto
described by Cowan and Rowell. If the departures are small,
measure the spectral power distributions and reduce them to
they may be neglected or a LUT correction applied. If the
CIE tristimulus values. Practice E1455 describes how to
departuresaresignificantandmaximumreproductionaccuracy
measure the CIE tristimulus values of the primaries directly.
is required, only a full table look-up method can be used to
An exact characterization of the VDU would require measure-
create the RGB to XYZ transform.
ment of the spectral power distribution at all possible combi-
6.1.2 Assumption 2, spatial invariance, can be tested by
nations of primary settings. Modern, computer-controlled
VDUs will provide 256 or more levels of each of the three measuring the center of a dark display and then repeating the
measurements with pixels near the edge of the display illumi-
primaries. This results in more than 16777000 unique
settings, which is far too many combinations to be measured nated fully. The display may have to be considered unusable
for critical applications if this assumption is not met. The
practically (see Note 1). Instead, a characteristic function
relating the radiant output of the screen to the digital inputs amount of spectral variance will be a function of both position
andintensityofboththeareaofinterestandtheintegratedarea
fromthecomputermustbederived.Proceduresareoutlinedfor
deriving a characteristic function for a computer-controlled of pollution. While such models can be derived, they may be
too complex to justify their use.
VDU, using a minimum number of spectral radiometric mea-
surements while maintaining near optimum accuracy. Ex-
6.1.3 Assumption3,levelinvariance,istestedbymeasuring
amples of deriving and testing such models are given in
the chromaticity of a primary at several different levels. It
Appendix X1.
should be noted that care must be taken to maintain the signal
to noise value of the color measuring instrument as the
NOTE 1—Different primary settings do not necessarily produce percep-
luminance of the primary is reduced. As the signal level of a
tibly different colors. For VDUs with a large number (for example,
16777000) of different primary settings, the number of perceptibly
colorimeterapproachestheoptical/electricalzero,theapparent
different colors will be less than the number of primary settings.
chromaticity approaches that of neutral black.
6.1.4 Assumption 4, absence of inter-reflections, is often
5. Significance and Use
violated on CRT-type displays without high efficiency antire-
5.1 ThecolordisplayedonaVDUisanimportantaspectof
flection(HEA)coatingsonthefaceplategloss.Thisisdetected
the reproduction of colored images. The VDU is often used as
in the same manner as spatial invariance. Again, models for
the design, edit, and approval medium. Images are placed into
this can be derived, but the complexity may not be worth the
the computer by some sort of capture device, such as a camera
effort.
or scanner, modified by the computer operator, and sent on to
6.1.5 Assumption5,linearityoftheDAC,canbetestedwith
a printer or color separation generator, or even to a paint
a calibrated, high-precision oscilloscope. A doubling of the
dispenser or textile dyer. The color of the final product is to
digital counts should produce a doubling of the output signal.
have some well-defined relationship to the original. The most
It should be noted that RS-170 voltage levels are from −0.286
common medium for establishing the relationship between
V to +0.714 V with the range from 0 V to 0.714 V being used
input, edit, and output color (device-independent color space)
for signal level and 0 V to −0.286 V being used for synchro-
is the CIE tristimulus space. This guide identifies the proce-
nization during the blanking interval on a CRT-type display.
dures for deriving a model that relates the digital computer
Other types of visual display units may have their own unique
settings of a VDU to the CIE tristimulus values of the colored
voltage ranges as well. In general, the setting of the drive
light emitted by the primaries.
voltage requires the simultaneous alignment of many opera-
tional parameters, the specification of which are beyond the
6. Models
scope of this guide. It is assumed that the signal generator and
the receiver are adjusted to be within their unique operational
6.1 The models are based on eight basic assumptions. First,
specifications before the linearity test is performed.
at each pixel location on the VDU, the radiant exitance
(emitted light per unit area) attributable to one primary type 6.1.6 Assumption 6, ambient glare, can be tested with a
(red, green, or blue) is invariant with the radiant exitances of
telephotometer, measuring the luminance and chroma of each
the other primary types. Second, the radiance exitance at one primaryinadarkandambientenvironment.Ifthetworeadings
spatial location is invariant with the radiant exitance at other
spatiallocations.Third,therelativespectralradiantexitanceof
a primary is invariant with excitation level. Fourth, there is no
Cowan, W. B., and Rowell, N., “On the Gun Independence and Phosphor
inter-reflection of light between pixel locations. Fifth, the
Constancy of Colour Video Monitors,” Color Research and Application, Vol 11,
output of the digital-to-analog conversion process is linear. 1986, pp. S35–S38.
E1682 − 08 (2018)
differ by an unacceptable amount, either the display must be 6.3.1 Following the procedures given in Test Method
outfitted with light shields or its operation restricted to a dark E1336, the spectroradiometer will measure the spectral radi-
environment. ance (L ) of an extended diffuse source, such as a VDU. The
λ
6.1.7 Assumption 7, flicker rate, is a function of the display spectral radiance is related to the spectral exitance as follows:
electronics and display type. Chromatic flicker ceases at
M
λ
L 5 (2)
frequencies above 30 Hz. Brightness flicker ceases for most
λ
π
people above 60 Hz, although some people continue to
6.3.2 The radiance for each primary can be described as
experience the sensation of flicker up to 70 Hz. Most modern
follows:
graphics displays operate at refresh rates above 60 Hz. Broad-
cast displays may operate at rates as low as 30 Hz. Low-rate
L 5 RL , L 5 GL , L 5 BL
λ,r λ,r,max λ,g λ,g,max λ,b λ,b,max
display electronics interfaced to a high-rate display may result
The scalars R, G, and B can be thought of as the display
in an unacceptable appearance.
tristimulus values. From Test Method E1336, we obtain the
6.1.8 Assumption 8, pixel density, is a characteristic of the
relationship between the measured spectral radiance and the
displayandafunctionoftheapplication.Alow-densitydisplay
CIE tristimulus values, in luminance units as follows:
may be adequate for displaying solid patches of color but not
830 830
for detailed drawings or renderings.
X 5683 L x¯ dλ 5683R L x¯ dλ (3)
* *
r λ,r λ λ,r,max λ
6.2 Examples of using the LUT method are also given in
360 360
this guide for completeness. There are three possible ap-
830 830
proaches to modeling the relationship between the digital
Y 5683 L y¯ dλ 5683R L y¯ dλ
* *
r λ,r λ λ,r,max λ
counts and the VDU tristimulus values. The first requires the
360 360
user to adjust the video gain and offset manually such that the
830 830
blacklevelandtheoffsetcanceleachother.Thesecondmethod
Z 5683 * L z¯ dλ 5683R * L z¯ dλ
r λ,r λ λ,r,max λ
tries to approximate the gain and offset by trial and error. The
360 360
third method, the one used most commonly commercially,
6.3.3 The linear superposition of the red, green, and blue
ignores the physical origins of the signals and collects mea-
tristimulus values yield the following:
surements of the VDU output at a large number of points,
sampling each primary channel between the minimum and
X 5683 * L 1L 1L x¯ dλ (4)
maximum counts. The unmeasured data values are determined ~ !
λ,r λ,g λ,b λ
by interpolation, and a LUT is formed such that all possible
combinationsofprimarysettingscanbefoundinthetable.The
5RX 1GX 1BX
r,max g,max b,max
recommendedprocedureinthisguideconformsmostcloselyto
the second method, using statistical methods to determine the
Y 5683 * ~L 1L 1L ! y¯ dλ
optimum parametric values for the gain, offset, and gamma of
λ,r λ,g λ,b λ
each primary while requiring the smallest number of calibra-
tionpatches.This,then,linearizestheoutputofthesystem,and
5RY 1GY 1BY
r,max g,max b,max
a linear transformation is applied to convert the linear RGB
primary values to CIE tristimulus values.
Z 5683 * L 1L 1L z¯ dλ
~ !
λ,r λ,g λ,b λ
6.3 The model parameters for the red primary are related to
the operational variables as follows:
5RZ 1GZ 1BZ
r,max g,max b,max
γ
d
r
M 5 M k 1k (1)
F S D G
λ,r λ,r,max g,r N o,r
In matrix notation, these equations can be reduced to the
2 21
following:
where:
X X X X R
r,max g,max b,max
M = the spectral exitance of the (r)ed primary,
λ,r
Y Y Y Y G
5 (5)
r,max g,max b,max
M = the maximum spectral exitance of the (r)ed F G F GF G
λ,r,max
Z Z Z Z B
primary, r,max g,max b,max
d = the digital setting of the (r)ed primary,
r
where R, G, and B are defined as follows:
N
2 −1 = the number of digital states generated by the
γ
d
r
display driver,
R 5 max k 1k ,0 (6)
F H S D JG
g,r n o,r
2 21
k = thesystem(g)aincoefficientforthe(r)edprimary,
g,r
k = the system (o)ffset coefficient for the (r)ed
o,r
γ
d
g
primary, and
G 5 max k 1k ,0
F H S n D JG
g,g o,g
2 21
γ = the system gamma coefficient.
γ
Similar expressions can be derived for the green and blue d
b
B 5 max k 1k ,0
F H S D JG
g,b n o,b
primaries. 2 21
E1682 − 08 (2018)
Being linear, Eq 5 can be solved for R, G, B. Thus the 7). That completes the model. Given any set of DAC values,
inverse is given, in matrix notation, as follows: the model will predict the XYZ for that setting, and given any
21 XYZvalues, the model will predict the D
...