1、Designation: E1455 16Standard 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 the case of revisio
2、n, 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 tristimulus colorimeterswhen
3、 measuring the tristimulus values or chromaticity coordinates of colored displays. Tristimuluscolorimeters approximate the CIE color matching functions (), (), () to make these measurements.The errors generated in measuring colors on a display may be minimized using this practice.1. Scope1.1 This pr
4、actice 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 takesadvantage of t
5、he 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 criteria as define
6、d 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, associated with it
7、s 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 Method for Obtaining Colorimet
8、ric Data From aVisual Display Unit by SpectroradiometryE1341 Practice for Obtaining Spectroradiometric Data fromRadiant Sources for Colorimetry2.2 ISO/CIE Standard:ISO 116641:2007(E)/CIE S 0141/E:2006 Joint StandardISO/CIE Standard: Colorimetry Part 1 CIE StandardColorimetric Observers33. Terminolog
9、y3.1 DefinitionsUnless 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 tristimuluscolorimeter, the process performed outside of this practice toadjust the tr
10、istimulus colorimeter to provide the best possibleresults for average or predefined conditions.3.2.2 optimization, nin reference to a tristimuluscolorimeter, the process performed pursuant to this practice toadjust the tristimulus colorimeter or to interpret its readings toprovide better results whe
11、n applied to a particular displaydevice.3.2.3 compatible, adjin reference to a tristimuluscolorimeter, one so designed as to automate the proceduredescribed in this practice.4. Summary of Practice4.1 Tristimulus colorimeters comprised of three or fourdetector channels are, in general, not amenable t
12、o accuratecalibration that holds for all manner of usage with different1This practice is under the jurisdiction of ASTM Committee E12 on Color andAppearance and is the direct responsibility of Subcommittee E12.06 on Display,Imaging and Imaging Colorimetry.Current edition approved July 1, 2016. Publi
13、shed August 2016. Originallyapproved in 1992. Last previous edition approved in 2010 as E1455 03 (2010).DOI: 10.1520/E1455-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information,
14、 refer to the standards Document Summary page onthe ASTM website.3Currently available from CIE (Commission International on Illumination),http:/.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1illuminated devices and objects. This is
15、because the spectralresponsivities of their detector channels do not exactly matchthe defined Commission Internationale de Lclairage (CIE)(), (), () functions. Factory or subsequent calibration reflectsjudgments and compromises that may not be readily apparent.Nevertheless, this practice provides gu
16、idance on how such atristimulus colorimeter may be optimized for use with aparticular video display device, providing 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 value
17、s that are closerto the ideal. This matrix is determined by reference to acolorimeter with higher intrinsic accuracy. 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
18、 and Use5.1 This practice may be applied when tristimulus colorim-eters are used to measure the colors produced on self-luminousvideo display devices such as CRTs and flat-panel displays,including electroluminescent (EL) panels, light emitting diodes(LEDs) field emission displays (FEDs), and back-li
19、t liquidcrystal displays (LCDs). This practice is not meant to be acomplete description of a procedure to measure the colorcoordinates of a display. Rather, it provides a method forobtaining more accurate results when certain conditions aremet. It may be used by any person engaged in the measurement
20、of color on display devices who has access to the requisiteequipment.5.2 This practice defines a class of tristimulus colorimetersthat may 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
21、radiometric power as transmitted through anumber of bandpass filters. Most commonly, electrical devicesare used to measure the filtered light. They may be used withdifferent filters in succession, or multiple devices may be usedconcurrently. In instruments called spectroradiometers, theradiometric p
22、ower is measured through a large number (typi-cally 30 to 500) of narrowband filters. (Practice E1341 de-scribes how a monochromator or polychromator (spectrograph)may be employed to filter and measure light in separate bandson the order of 1-nm wide.) In instruments called tristimuluscolorimeters,
23、the radiometric power is measured through threeor four wideband filters. These filters may be constructed fromdispersive elements (prisms and gratings) or from materialswith selective spectral transmission or reflection. The lattermay be either uniform or comprised of different patches, in amosaic p
24、attern, that provide the desired overall effect.6.1.2 No matter how many filters are used, or in whatmanner, the goal of the measurement process is to determinetristimulus values X, Y, Z, as defined by ISO in its StandardISO 116641:2007(E)/CIE S 0141E:2006 and the CIE in itspublication Publ. 015(1).
25、4For light with a color stimulusfunction (),X 5 k *360 nm830 nm!x!d (1)Y 5 k *360 nm830 nm!y!dZ 5 k *360 nm830 nm!z!dwhere:k is 683 lm/W for emissive devices, such as displays, and x!,y!, z! are color-matching functions. While the standarddefinition of X, Y, Z requires the use of the CIE 1931 2color
26、-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 In practice, color measurement instruments computeX, Y, Z by the summation of the signals as measured throughthe various filte
27、rs, each signal being multiplied by an appro-priate calibration factor. In matrix notation:FXmYmZmG5FCX1CX2CX3.CXfCY1CY2CY3.CYfCZ1CZ2CZ3.CZfG3F1F2F3Ff4(2)where:F1, F2, F3, through Ffare the electrical signals from the ffiltered detectors and the Cijare calibration coefficients. Xm,Ym, Zmhave subscri
28、pts 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 strictly proportionalto the received optical power, that any zero-offset (backgroundin darkness) is removed, that the proportiona
29、lity 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 Faspills over and affectssignal Fbas it approaches saturation. These presumptions areamenable to experimental verification using me
30、thods 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 of the instrument. The full extent of this subject isbeyond the scope of this practice. However, in general, forspectroradiometer
31、s (f 30 to 500), CXjreflects the tabulatedvalue of () near the center wavelength of Filter j as well as thespectral responsivity of the corresponding detector channel.(Likewise, CYjand CZjvary with ().) For tristimuluscolorimeters, the choice of Cijis discussed further, below. As a4The boldface numb
32、ers in parentheses refer to the list of references at the end ofthis standard.E1455 162general matter, the instrument designer should choose pass-bands and matrix elements that balance accuracy, sensitivity,and other design requirements.6.1.6 Tristimulus colorimeters are generally designed withfilte
33、rs that are intended to match the spectral responsivities oftheir detector channels to the CIE color matching functions.For such an instrument,FXmYmZmG5FCX1000 CY2000CZ3GFF1F2F3G(3)where:the non-zero Cijmatrix elements represent adjustable gains ofthe detector channels. However, the x() function has
34、 twodistinct lobes. This may be dealt with by splitting the lobes intotwo functions, xshort() and xlong(), each with a separate filter(F1and F2, respectively). For such an instrument,FXmYmZmG5FCX1CX20000CY30000CZ4G3F1F2F3F44Alternatively, the z() function properly scaled may serve asthe xshort(), si
35、nce they have a similar shape,FXmYmZmG5FCX10 CX30 CY2000CZ3GFF1F2F3GIn all of these cases, it is difficult to realize 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 perfe
36、ct 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 generally believed that spectroradiometers, withtheir many detector channels, may be calibrated to yieldsuperior measurements of X, Y, Z for dive
37、rse applications.Nevertheless, the relative simplicity of tristimulus colorimetersand their commensurately lower cost 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 e
38、mission display (FED), lightemitting diodes (LED) or a back-lit liquid crystal display(LCD) generates colored light by the proportional superposi-tion (addition) of primary colored lights r(), g(), b().The subscripts represent red, green, and blue, the primarycolors of an additive set. An arbitraril
39、y colored patch on thevisual display has one and only one color stimulus function(),! 5 ar!1bg!1cb! (6)where a, b, care coefficients 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 pra
40、ctice,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 display to permitmeasurements to be made on that area.6.2.3 It is a requirement for the applicability of this practicethat the display dev
41、ice 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 classesof devices might do so. The procedure for experimentalverification of this property for a specific display device isbeyond the scop
42、e of this practice (3).6.3 Colorimetric Measurement of Displays:6.3.1 Each of the primary color stimulus functions r(),g(), b() stimulates responses in the f detector channels thatmay be represented by a vector F (that is, Fr, Fg, Fb). Giventheir construction, these vectors are linearly independent.
43、(None of the three can be expressed as a linear combination ofthe other two.) While F is an element of an f-dimensionalvector space, it is clear that only a three-dimensional subspaceis spanned by the Fs of all possible color stimulus functionsfollowing Eq 6. Further, the mapping of F into (Xm, Ym,
44、Zm)space by Eq 2 remains three dimensional. In other words, thereis a one-to-one mapping of the vector (a, b, c) onto (X, Y, Z)byapplication of Eq 1; and, for a particular instrument with afixed calibration matrix C, there is also a one-to-one mappingof the vector (a, b, c) onto (Xm, Ym, Zm). From t
45、his we deducethat a matrix R exists that can be used to translate (Xm, Ym, Zm)values into actual (X, Y, Z) values.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 thecomput
46、ation 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 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
47、 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 stable, andthat similarly built displays have similar enough spectralprimaries to make a derivation of R worthwhile. However,these assumptions sho
48、uld be quantified before accuracy claimsare made in any specific situation.6.3.4 On the basis of this property, 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 responsivit
49、ies 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 r(), g(), b().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,Zmfrom the colorimeter being optimized, for a number of colorsamples at differen
