1、Designation: E 1455 03Standard Practice forObtaining Colorimetric Data from a Visual Display UnitUsing Tristimulus Colorimeters1This standard is issued under the fixed designation E 1455; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revis
2、ion, 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.INTRODUCTIONThis practice provides directions for correcting the results obtained with tristimulus colorimetersw
3、hen measuring the tristimulus values or chromaticity coordinates of colored displays. Tristimuluscolorimeters approximate the CIE color matching functions x (l), y (l), z (l) to make thesemeasurements. The errors generated in measuring colors on a display may be minimized using thispractice.1. Scope
4、1.1 This practice is intended as an aid for improving theaccuracy of colorimetric measurements made with tristimuluscolorimeters on visual display units, such as cathode ray tubes(CRTs) and self-luminous flat-panel displays. It explains auseful step in the analysis of colorimetric data that takesadv
5、antage of the fact that light from such displays consists ofan additive mixture of three primary colored lights. However,it is not a complete specification of how such measurementsshould be made.1.2 This practice is limited to display devices and colori-metric instruments that meet linearity criteri
6、a as defined in thepractice. It is not concerned with effects that might causemeasurement bias such as temporal or geometric differencesbetween the instrument being optimized and the instrumentused for reference.1.3 This standard does not purport to address all of thesafety concerns, if any, associa
7、ted 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 Standards:2E 284 Terminology of AppearanceE 1336 Test Method for Obtain
8、ing Colorimetric Data froma Video Display Unit by SpectroradiometryE 1341 Practice for Obtaining Spectroradiometric Datafrom Radiant Sources for Colorimetry2.2 ISO/CIE Standard:CIE Standard Colorimetric Observers, ISO/CIE10527: 1991 (E) (International Organization for Stan-dardization, Geneva, 1991)
9、33. Terminology3.1 Definitions: Unless otherwise stated, definitions of ap-pearance terms in Terminology E 284 are applicable to thispractice.3.2 Definitions of Terms Specific to This Standard:3.2.1 calibration, n in reference to a tristimulus colorim-eter, the process performed outside of this prac
10、tice to adjust thetristimulus colorimeter to provide the best possible results foraverage or predefined conditions.3.2.2 optimization, n in reference to a tristimulus colo-rimeter, the process performed pursuant to this practice toadjust the tristimulus colorimeter or to interpret its readings topro
11、vide better results when applied to a particular displaydevice.3.2.3 compatible, adj in reference to a tristimulus colo-rimeter, one so designed as to automate the procedure de-scribed in this practice.4. Summary of Practice4.1 Tristimulus colorimeters comprised of three or fourdetector channels are
12、, in general, not amenable to accurate1This practice is under the jurisdiction of ASTM Committee E12 on Color andAppearance and is the direct responsibility of Subcommittee E12.06 on Appearanceof Displays.Current edition approved Dec. 1, 2003. Published January 2004. Originallyapproved in 1992. Last
13、 previous edition approved in 1997 as E 1455 97.2For 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 the standards Document Summary page onthe ASTM website.3Currently av
14、ailable through the U.S. National Committee of the CIE, c/o Mr.Thomas M. Lemons, TLA-Lighting Consultants, Inc., 7 Pond Street, Salem, MA01970-4819. Also included in ASTM Standards on Color and Appearance, FifthEdition, 1996.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Con
15、shohocken, PA 19428-2959, United States.calibration that holds for all manner of usage with differentilluminated devices and objects. This is because the spectralresponsivities of their detector channels do not exactly matchthe defined Commission Internationale de Lclairage (CIE) x(l), y(l), z (l) f
16、unctions. Factory or subsequent calibrationreflects judgments and compromises that may not be readilyapparent. Nevertheless, this practice provides guidance on howsuch a tristimulus colorimeter may be optimized for use with aparticular video display device, providing better accuracy withthat device
17、than its more general calibration provides. Anoptimization matrix transforms the instrumental (measured)CIE X, Y, Z values into adjusted X, Y, Z values that are closerto the ideal. This matrix is determined by reference to acolorimeter with higher intrinsic accuracy. The method derivesfrom the fact
18、that the color stimulus functions from displaydevices are linear combinations of three primary functions andare not entirely arbitrary.5. Significance and Use5.1 This practice may be applied when tristimulus colorim-eters are used to measure the colors produced on self-luminousvideo display devices
19、such as CRTs and flat-panel displays,including electroluminescent (EL) panels, field emission dis-plays (FEDs), and back-lit liquid crystal displays (LCDs). Thispractice is not meant to be a complete description of aprocedure to measure the color coordinates of a display. Rather,it provides a method
20、 for obtaining more accurate results whencertain conditions are met. It may be used by any personengaged in the measurement of color on display devices whohas access to the requisite equipment.5.2 This practice defines a class of tristimulus colorimetersthat may be said to be compatible with this pr
21、actice.6. Background of Practice6.1 Colorimetry:6.1.1 Color measurement instruments consist, in general, ofmeans to measure radiometric power as transmitted through anumber of bandpass filters. Most commonly, electrical devicesare used to measure the filtered light. They may be used withdifferent fi
22、lters in succession, or multiple devices may be usedconcurrently. In instruments called spectroradiometers, theradiometric power is measured through a large number (typi-cally 30 to 500) of narrowband filters. (Practice E 1341describes how a monochromator or polychromator (spec-trograph) may be empl
23、oyed to filter and measure light inseparate bands on the order of 1-nm wide.) In instrumentscalled tristimulus colorimeters, the radiometric power is mea-sured through three or four wideband filters. These filters maybe constructed from dispersive elements (prisms and gratings)or from materials with
24、 selective spectral transmission orreflection. The latter may be either uniform or comprised ofdifferent patches, in a mosaic pattern, that provide the desiredoverall effect.6.1.2 No matter how many filters are used, or in whatmanner, the goal of the measurement process is to determinetristimulus va
25、lues X, Y, Z, as defined by ISO in its Stan-dard 10527 and the CIE in its publication No. 15.2 (1).4Forlight with a color stimulus function F(l),X 5 k*360 nm830 nmFl!xl!dl (1)Y 5 k*360 nm830 nmFl!yl!dl (1)Z 5 k*360 nm830 nmFl!zl!dl (1)where:k is 683 lm/W for emissive devices, such as displays, and x
26、 (l),y (l), z (l) are color-matching functions. While the standarddefinition of X, Y, Z requires the use of the CIE 1931 2color-matching functions, the mathematics described in thispractice would also be applicable to any other set of color-matching functions, such as the CIE 1964 10 functions.6.1.3
27、 In practice, color measurement instruments computeX, Y, Z by the summation of the signals as measured throughthe various filters, each signal being multiplied by an appro-priate calibration factor. In matrix notation:FXmYmZmG5FCX1CX2CX3.CXfCY1CY2CY3.CYfCZ1CZ2CZ3.CZfG3F1F2F3AFf4(2)where:F1, F2, F3,
28、through Ffare the electrical signals from the ffiltered detectors and the Cijare calibration coefficients. Xm,Ym, Zmhave subscripts to indicate that they are measuredvalues rather than ideal ones.6.1.4 In this practice, we presume that the color measuringinstrument is linear: that each signal Fais s
29、trictly proportionalto the received optical power, that any zero-offset (backgroundin darkness) is removed, that the proportionality for signal Fais not affected by the value of signal Fb, and in the case ofclosely packed detectors (such as charge-coupled device(CCD) detector elements) no signal Fas
30、pills over and affectssignal Fbas it approaches saturation. These presumptions areamenable to experimental verification using methods beyondthe scope of this practice (2).6.1.5 The values of the matrix elements Cijmay be deter-mined using criteria that depends on the design and intendedapplication o
31、f the instrument. The full extent of this subject isbeyond the scope of this practice. However, in general, forspectroradiometers (f 30 to 500), CXjreflects the tabulatedvalue of x (l) near the center wavelength of Filter j as well asthe spectral responsivity of the corresponding detector channel.(L
32、ikewise, CYjand CZjreflect y (l) and z (l), respectively.) Fortristimulus colorimeters, the choice of Cijis discussed further,below. As a general matter, the instrument designer shouldchoose passbands and matrix elements that balance accuracy,sensitivity, and other design requirements.6.1.6 Tristimu
33、lus colorimeters are generally designed withfilters that are intended to match the spectral responsivities oftheir detector channels to the CIE x (l), y (l), z (l) functions.For such an instrument,4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.E145503
34、2FXmYmZmG5FCX1000 CY2000CZ3GFF1F2F3G(3)where:the non-zero Cijmatrix elements represent adjustable gains ofthe detector channels. However, the x (l) function has twodistinct lobes. This may be dealt with by splitting x (l) intoxshort(l) and xlong(l), each with a separate filter (F1and F2,respectively
35、). For such an instrument,FXmYmZmG5FCX1CX20000CY30000CZ4G3F1F2F3F44(4)Alternatively, the z (l) function may serve the role ofxshort(l) since they have a similar shape,FXmYmZmG5FCX10 CX30 CY2000CZ3GFF1F2F3G(5)In all of these cases, it is difficult to realize an exact matchbetween the CIE color-matchi
36、ng functions and the actualspectral responsivities of the corresponding detector channels.This means that no choice of Cijwill provide perfect calibra-tion for all applications of the instrument. The criteria forsetting the Cijmight not be well documented for a particularinstrument.6.1.7 It is gener
37、ally believed that spectroradiometers, withtheir many detector channels, may be calibrated to yieldsuperior measurements of X, Y, Z for diverse applications.Nevertheless, the relative simplicity of tristimulus colorimetersand their commensurately lower cost have made them popularwhere the highest ac
38、curacy is not required.6.2 Self-Luminous Displays:6.2.1 A self-luminous display, such as a CRT, an electrolu-minescent (EL) panel, a field emission display (FED), or aback-lit liquid crystal display (LCD) generates colored light bythe proportional superposition (addition) of primary coloredlights Fr
39、(l), Fg(l), Fb(l). The subscripts represent red,green, and blue, the primary colors of an additive set. Anarbitrarily colored patch on the visual display has one and onlyone color stimulus function F(l),Fl! 5 aFrl! 1 bFgl! 1 cFbl! (6)where a, b, c are coefficients that are determined by thedisplay e
40、lectronics.6.2.2 The display electronics vary a, b, c over the face of thedisplay in order to generate a colored image. For this practice,we presume that the display electronics may be set to make a,b, c uniform (perhaps after averaging nonobvious fine-structure) over a sufficient area of the displa
41、y to permitmeasurements to be made on that area.6.2.3 It is a requirement for the applicability of this practicethat the display device behaves as stated in Eq 6. This practicedoes not represent that any particular display device will act aspredicted by Eq 6, though those within the mentioned classe
42、sof devices might do so. The procedure for experimentalverification of this property for a specific display device isbeyond the scope of this practice (3).6.3 Colorimetric Measurement of Displays:6.3.1 Each of the primary color stimulus functions Fr(l),Fg(l), Fb(l) stimulates responses in the f dete
43、ctor channelsthat may be represented by a vector F (that is, Fr, Fg, Fb).Given their construction, these vectors are linearly indepen-dent. (None of the three can be expressed as a linear combi-nation of the other two.) While F is an element of anf-dimensional vector space, it is clear that only a t
44、hree-dimensional subspace is spanned by the Fs of all possiblecolor stimulus functions following Eq 6. Further, the mappingof F into (Xm, Ym, Zm) space by Eq 2 remains three dimen-sional. In other words, there is a one-to-one mapping of thevector (a, b, c) onto (X, Y, Z) by application of Eq 1; and,
45、 fora particular instrument with a fixed calibration matrix C, thereis also a one-to-one mapping of the vector ( a, b, c) onto (Xm,Ym, Zm). From this we deduce that a matrix R exists that can beused to translate (Xm, Ym, Zm) values into actual (X, Y, Z)values.6.3.2 A colorimeter that takes advantage
46、 of this fact mustprovide means for implementing the matrix R. That is, all ffiltered detector signals should contribute linearly toward thecomputation of each output, Xm, Ym, Zm, instead of usingdifferent detectors for each output. This idea was reported aslong ago as 1973 by Wagner (4), and it has
47、 been expandedupon and rediscovered by others since then (5-10).6.3.3 On the basis of this property, a tristimulus colorimetercan be optimized for use on a self-luminous display by theproper derivation of a matrix R for that display. We proceed onthe assumptions that the components are sufficiently
48、stable, andthat similarly built displays have similar enough spectralprimaries to make a derivation of R worthwhile. However,these assumptions should be quantified before accuracy claimsare made in any specific situation.6.3.4 On the basis of this property, a tristimulus colorimeterdesigned for use
49、with displays need not produce signals F thatare close to CIE tristimulus values. Signal/noise may beimproved by matching the spectral responsivities of the filtereddetectors to the emission spectra of the primary colors. In suchdesigns, it is especially important to use a matrix R that isspecific to the particular Fr(l), Fg(l), Fb(l).7. Optimization7.1 General:7.1.1 Given the existence of a matrix R, how is it deter-mined? Experimentally, the problem is one of comparing thedata X, Y, Z from a reference colorimeter with the data Xm, Ym,Zmfro
