1、Designation: E1455 03 (Reapproved 2010)Standard Practice forObtaining Colorimetric Data from a Visual Display UnitUsing Tristimulus Colorimeters1This standard is issued under the fixed designation E1455; the number immediately following the designation indicates the year oforiginal adoption or, in t
2、he case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONThis practice provides directions for correcting the results obtained with tristimulu
3、s colorimeterswhen 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 thispr
4、actice.1. Scope1.1 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 dat
5、a that takesadvantage 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 li
6、nearity criteria 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,
7、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 Standards:2E284 Terminology of AppearanceE1336 Test Meth
8、od for Obtaining Colorimetric Data Froma Visual Display Unit by SpectroradiometryE1341 Practice for Obtaining Spectroradiometric Data fromRadiant Sources for Colorimetry2.2 ISO/CIE Standard:CIE Standard Colorimetric Observers, ISO/CIE10527: 1991 (E) (International Organization for Stan-dardization,
9、Geneva, 1991)33. Terminology3.1 Definitions: Unless otherwise stated, definitions of ap-pearance terms in Terminology E284 are applicable to thispractice.3.2 Definitions of Terms Specific to This Standard:3.2.1 calibration, nin reference to a tristimulus colorim-eter, the process performed outside o
10、f this practice to adjust thetristimulus colorimeter to provide the best possible results foraverage or predefined conditions.3.2.2 optimization, nin reference to a tristimulus colorim-eter, the process performed pursuant to this practice to adjustthe tristimulus colorimeter or to interpret its read
11、ings toprovide better results when applied to a particular displaydevice.3.2.3 compatible, adjin 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 cha
12、nnels are, 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 ImageBased Color Measurement.Current edition approved March 1, 2010. Published March 2010. Originallyapprove
13、d in 1992. Last previous edition approved in 2003 as E1455 03. DOI:10.1520/E1455-03R10.2For 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 Summar
14、y page onthe ASTM website.3Currently available 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 B
15、arr Harbor Drive, PO Box C700, West Conshohocken, 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
16、 de Lclairage (CIE) x(l), y (l), z (l) functions. 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, pr
17、oviding better accuracy withthat device 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 ac
18、curacy. The method derivesfrom the fact 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 produce
19、d on self-luminousvideo display devices 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 o
20、f a display. Rather,it provides a method 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 m
21、ay be said to be compatible with this practice.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
22、light. They may be used withdifferent filters 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 E1341 de-scribes how a monochromator or
23、polychromator (spectrograph)may be employed to filter and measure light in separate bandson the order of 1-nm wide.) In instruments called tristimuluscolorimeters, the radiometric power is measured through threeor four wideband filters. These filters may be constructed fromdispersive elements (prism
24、s and gratings) or from materialswith selective spectral transmission or reflection. The lattermay be either uniform or comprised of different patches, in amosaic pattern, that provide the desired overall effect.6.1.2 No matter how many filters are used, or in whatmanner, the goal of the measurement
25、 process is to determinetristimulus values X, Y, Z, as defined by ISO in its Standard10527 and the CIE in its publication No. 15.2 (1).4For lightwith 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 emiss
26、ive devices, such as displays, and x (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, suc
27、h as the CIE 1964 10 functions.6.1.3 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.
28、CZfG3F1F2F3AFf4(2)where:F1, F2, F3, 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 measuringinstrumen
29、t is linear: that each signal Fais strictly 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(C
30、CD) detector elements) no signal Faspills 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
31、the design and intendedapplication of 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 t
32、he corresponding detector channel.(Likewise, 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 othe
33、r design requirements.6.1.6 Tristimulus colorimeters are generally designed withfilters that are intended to match the spectral responsivities of4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.E1455 03 (2010)2their detector channels to the CIE x (l), y
34、 (l), z (l) functions.For such an instrument,FXmYmZmG5FCX1000 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 w
35、ith a separate filter (F1and F2,respectively). 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 realiz
36、e an exact matchbetween the CIE color-matching 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
37、for a particularinstrument.6.1.7 It is generally 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 cos
38、t have made them popularwhere the highest accuracy 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 superpos
39、ition (addition) of primary coloredlights Fr(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 coef
40、ficients that are determined by thedisplay electronics.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-str
41、ucture) over a sufficient area of the display 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
42、 6, though those within the mentioned classesof 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(
43、l), Fb(l) stimulates responses in the f detector 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-dimensi
44、onal vector space, it is clear that only a three-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)
45、 onto (X, Y, Z) by application of Eq 1; and, 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)val
46、ues.6.3.2 A colorimeter that takes advantage 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
47、aslong ago as 1973 by Wagner (4), and it has 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 assum
48、ptions that the components are sufficiently 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
49、, a tristimulus colorimeterdesigned for use 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 re
