GB/T 7921—1997
This standard is a revision of GR7921—1997 according to the relevant provisions of the International Commission on Illumination publication CIIE Co.15.2 (1986) 6 Colorimetry. The technical content is consistent with the uniform color space and color difference formula of CIE Colorimetry. When this standard was revised according to GB/T1.1 1993 Guidelines for Standardization, relevant reference standards were added in the compilation of the standard: the explanation of the points A, C, K, and F in the chromaticity diagram was supplemented; in the uniform color space, the contents of saturation, chroma, hue, hue difference, CIHI.UV color space and color difference units were added. This standard is a basic colorimetry standard and should be used in conjunction with GI3/T3977—1997, GI3/T397894 and GB/T39791997
This standard will replace GB7921—1997 from the date of entry into force. Appendix A of this standard is the appendix of the standard.
This standard is proposed and approved by the National Technical Committee for Color Standardization. This standard is initiated by the Chinese Academy of Design Sciences, and the drafters are Teng Xiujin, Pu Xiaodong, and Hu Wei: 1 Scope
National Standard of the People's Republic of China
Uniform colour space and
colour difference formula
GB/T 7921—1997
Replaces GB7921—87
This standard specifies the visually approximate uniform CIE197 (1\) and CIE1976 (L\) colour spaces and the corresponding colour difference formulas.
This standard is applicable to the representation of all light source colours and object colours, as well as the representation and calculation of colour differences. 2 Cited standards
The clauses contained in the following standards constitute the clauses of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised. Parties using this standard should explore the possibility of using the latest versions of the following standards. G13/T3977—1997 Color measurement method GB/T3978—94: Standard illuminant and lighting observation conditions (G13/3979—1997 Measurement method of object color GB5698—85 Color terms
3 Definitions
This standard adopts the following definitions.
3. 1 Lightne5s index index
Symbol; L
In a three-dimensional color space that is visually uniform, it represents the coordinates of the color brightness of an object. 3.2 Chromaticity index chromaticity index symbol: ab\u,u
In a one-dimensional color space that is visually uniform, it represents the chromaticity coordinates of the color of an object and the color of a light source. Other color terms in this standard are in accordance with the provisions of (Letter 5698). 4 Uniform color space
4.1 CIE1976L color space (abbreviated as CIE ELUV color space) 4.7.1 CIE1976 uniform chromaticity diagram CIE1976u diagram) CIF1976 diagram is visually close to uniform, and is obtained by projecting the CIE1931 chromaticity diagram (see Figure 1). The abscissa and ordinate formulas are given in ().
In the diagram, A, C, IDe are the chromaticity points corresponding to the standard illuminant of colorimetry, and E is the chromaticity point of equal energy stimulation. Approved by the State Administration of Technical Supervision on May 4, 1997 and implemented on October 1, 1997
In the formula; XYZ-
GB/T 79211997
Figure 1CJE1!z Chromaticity Diagram (2 Fields of View)
X+1+82 or l=-2+12+3
l-X+1V+ 32 or ==2++12y+3]
Three stimulus values of a sample. When the field of view is between 1°4\, the three stimulus values X, Y, Z of the C1F1931 standard colorimetry system are used; when the field of view is greater than A, the three stimulus values Xiu, Ym7.m of the CIF 1964 standard colorimetry system are used
The sample corresponds to the trichromatic coordinates of the CIE1931 standard colorimetry system or the CIE1964 supplementary standard colorimetry system.
4.1.2CIEIUV color space
The approximately uniform CIELUV three-dimensional color space is composed of rectangular coordinates L",,,,, as shown in Figure 2. 4.1.3 Indigo index L
+* -- 116(Y/Y.)+ - 16.
Y/Y, 0.008 856
I - 903. 3 (Y/Y.))
Y/Y0.008856
In Y,-
GB/T 7921-1997
The chromaticity coordinates of the fully reflective diffuser in the XYZ chromaticity system or the XY chromaticity system are obtained by the following formula:
X. = 15Y. — 3z,
X. -15Y. + 3z.
In the formula: XYZ, -\.·The absolute value of the fully reflecting reflector in the XYZ colorimetry system or the XY.Z.. colorimetry system (see Table 3-4)
Saturation S..
S=13t(un)+(
Chroma Ca
Ch =(ur\+\)* =1\S
Hue angle,
tu = aretan[(t αl)/(ul u,)] = arclan(u*/u*)4. 1.8
Hue difference AH
AH =T(AE)\-(AL\)z(AC)
and A have the same positive and negative signs.
4.1.9 (IE1.IJV color space hue angle, hue difference and other corresponding parameters of the application rules see Appendix A (Standard Appendix). 4.2 CIE 1976 Lα'' color space (simplified CIELAB color space) 4.2.1 CIELAB color space
The CIELAB three-dimensional color space, which is approximately uniform, is composed of rectangular coordinates L\b (see Figure 3). L
Chengdian G
Constant S
Constant h
Figure 2 CIELUV color space
Lightness index L
Chromaticity index α\ and b
GB/T 7921
Figure CIELAH color space
L- - 116 (Y/Y.>7
Y/Y. > 0.008 856
1-903.3(Y/Y.)
Y/Y 0. 008 856
at = 5000f(X/X,)
- 200.(Y/Y) -/(/Z.)3
where;f(X/x.)-(X/X)
(X/X.20 . 008 856
or: /(X/X.)=7.787(X/X.)+16/116(X/X,) $ 0. 008 856
F(Y/Y)-(Y/Y,
(Y/Y.)0.008 856
or: f(Y/Y,)=7.787(Y/Y)+16/116S(Z/7.) - (Z/Z.>-
(Y/Y.) : 0. 008 856
(7/2.) 2 0. 008 856
7.787(2/Z.) — 16/116
or: (21%)
4.2.4 Chroma C
Hue angle Ha
Difference between chroma C and hue AA
4.2.7 Hue difference AH
(2/Z.)≤ 0.008 856
Ch =(a*+h+y1?
h = arctan(b'/a\)
ACl = C - C2.
Ahat - h.a6
H has the same positive and negative signs as A:
4.2.8 (The application rules of hue angle, hue difference and other corresponding parameters in IELAB color space are shown in Appendix A <Appendix of the Standard). 5. Representation of color in uniform color space 5.1 In CIELUV color space, color is represented by lightness index I.” and chromaticity index. [9》
(10）
-(12 )
·（15)
- 16 )
GB/T 79211997
5.2 In the CIFI.AB color space, color is represented by lightness index I· and chromaticity index u, b\. 5.3 For light source color, absolute photometry can be used to supplement it when necessary. 6 Color difference formula
6.1CIELUV color difference formula
AE= AL + (A-(A)2
Where: 45
The color difference between two colors in the CIELUV color space is the difference between the lightness index L and L of two colors: AL* -t
AA…The chromaticity index of two colors in the CIELUV color space is the difference between and: Au* = ut - u?
6.2CIFI.AH color difference formula
AE[(ALy 1 (A)2 + (A6')\7-2
where: A is the color difference between two colors in CIELAB color space AI is the brightness index of two colors in CIFTA color space.\The difference between AL -Lx- )
'”—The difference between the chromaticity index and the chromaticity index of two colors in the CIEIAB color space F: -ai-a
7 Methods for expressing color difference and color difference units
1 The color difference between the CIEIAB color space is expressed by F, and the color difference unit of the CIELAB color space is CIELAI3 Color difference unit: 7.2 The color difference between the CIFI.UV color space is expressed by AE. The color difference unit of the CIELUV color space is the CIELUV color difference unit. 7.3 The color difference value is taken to two decimal places
8 Methods for calculating color difference
To calculate the difference between two color samples, firstly, the one-color value and the three-color coordinates of the two samples should be calculated according to the provisions of B/T3979, and then the appropriate color difference formula should be selected for calculation. 8.1 Selecting the CIELUV color difference formula
8.1.1 Calculate the color difference of the sample using formula (1) Chromaticity coordinates z, 8.1.2 Calculate the lightness index L and L: of the sample according to formula (2) or (3): You can also look up Table 1 according to the Y value to directly obtain L: and L:, 8.1.3 Calculate the chromaticity index, and, of the sample according to formula (4). In the formula, and are obtained from Tables 3 and 4 8.1.4 Calculate the ALAu of the two samples "final", 8.1.5 Calculate the color difference AE of the two samples according to formula (17): 8.2 Use CIE L.AB color difference formula
8.2.1 Calculate the lightness index L and L of the sample according to formula (9) or (10). You can also directly obtain L and L according to the Y value by looking up Table 1. 8.2.2 Calculate the package index a, 5: and 2, of the sample according to formula (11) (the calculation can be simplified by using Table 2). 8.2.3 Calculate A△ and h of the two samples
8.2.4 Calculate the color difference △E value of the two samples according to formula (18). YY.
Gi- 1n
GB/T7921—1997
Y/Y and L conversion table
65, 12
54, 55
heart 2. 2.1
85, 50
CB/T7921
Table 1 (continued)||tt| |71: 08
75, 88
3e, 6s
: 100.00
(1. 519 2
96- 45
.98. 87
0, 507 9
GB/T 7921
End of table)
A/A. root table
G,235 1
0. 317 3 0, 321 8
0. 317 5,C. 330 3
U. -167 2
t, 3u9 2
G 20 3
0.384 9. 0. 3871
0. 1-13 1
.515 5
0, 582 8
C, 681
1 0. 766 3
GB/T 7921-1 997
Table 2 (continued)
0. 585 8 0.536 70. 587 7
(0. 604 6
n622 3
. 631
0. 655 t 0. 655 x
1.. 691 7
. 8324
11. 706 1
. 597
0. No. 61 3
0, 686 1
! 3. 73 5
0.743 5 :
: 0.744 1
(1, 755 4
0, 777 6
0,829 1
.831 9
6, 795 3||tt| |9, 661 5
G- 762 8
. 768 6
0, 815 5
(, 511 3
5, 591 :
(, 721 1
0, 757 ?
C.39C 63.5915
. 8i1 3
1 0.812 3.
. 816 8||tt| |c.831 1 1
0.843 30.843 8
G817 3
C-hoc o
0, 740 5
(0. 7-16 5
. 627 4
Total. 659 6
G602 R
3 6611
0. 702 7 0. 703 4
.0. 72 7
0- 764 6
C.77580.7764
0. 797 9 1
, 837 8
C. 0
9, 846 7
0, 848 1 . 848 6
bzxZ.net. 939 6
GB/T 7921
Table (End)
10. H49 5
: 0. 862 7
(,871 1
0, 88-1 1
. q090
U.047 3 0. 937 6
0.951 0 : 0.51 3
· 0.SER 6
. 358 3
0.961 90.952 3||t t||01. 993 3
. 991 2
(0. 872 4
88 7+ 6-881 1
0-884 9
0, 88 1
0. 9.36 8
. 06 &
1A/A. represents X/XY/Y.ziZ.
.893 8
.357 5
,868 5
: 0. 8K1 5
. 906 1
1 0. 536 5
. 956 1
C- 931 1||t t||C. 987 3 3. 087 6
951 3
(1. 853 9
0, 860 4
.951 8
0. 868 9 1 6859 3 0.269 8
0. 9: 5 0
0,8924
0, 593 9
p,9189
. 031 6
0. 05.1 2||tt| |G- 974 7
. 9a1 7
0, 991 9
. 995 3
2When 4/A is less than 0.00%856, the formula (3) can be used to calculate the first *L4. 923 3
. 91? 4
0 , 91s 9
. 668 0
CG. 919 7
03. 865 8
. 916 2
0. 927 50. 927 9| |tt||0, 939
0, 057 6
0. 978 9 1
0. 992 3. 992 6
0, 09 7
(10°)
GB/T7921·—1997
Table 3 Tristimulus values and chromaticity coordinates of a completely reflecting diffuser under standard illumination (a = 380 ~: 780 nr.4# - 5 nm)x
05, 01
Table 4 Tristimulus values and chromaticity coordinates of a fully reflective diffuser under standard illumination (a-380 y80nm .Ax=0 nm)
116,11
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