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The ColorChecker chart is made up of 24 color patches, arranged as four rows of six colors. The bottom row consists of six colors that are nominally neutral whose tones are approximately evenly distributed, visually speaking. Note that the "black" patch of the chart (lower right corner) is not really black, but rather, is a dark gray.
The third row from the top has some fairly saturated colors including primary colors (Blue, Green, Red) and secondary colors (Yellow, Magenta, Cyan).
The top row has a few "memory colors," such as skin tones, foliage and sky blue.
GretagMacbeth (the manufacturer of the ColorChecker chart) does not include a reference file with this chart, and when inCamera was first released, there was not a universally accepted format for such a file. So lacking a standard, we chose to use the same format that GretagMacbeth was using for the data reference files that they shipped with the ColorChecker DC chart. Using this format, we created a reference file for a typical ColorChecker chart and have included it in the inCamera product installation. That file is named ColorCheckerRefFile.txt.
More recently, GretagMacbeth has made a spectral data reference file for the ColorChecker chart available. It is named ColorChecker 24.txt, and we have included it in the inCamera installation package as well. inCamera now supports these spectral data reference files, and it also supports the older reference files that contain XYZ and Lab data.
You should use one of the included files in all cases except those where you have both the means and desire to create a custom reference file yourself. If you use the spectral reference file (ColorChecker 24.txt), you will also be able to specify your light source.
Power Users Only: Custom Data Reference Files
If you wish to make a custom reference file, it must be in the same file format as either ColorCheckerRefFile.txt or ColorChecker 24.txt. The contents of ColorCheckerRefFile.txt are shown here:
Date: 3/1/2001 Time: 09:53
LGOROWLENGTH 4
BEGIN_DATA_FORMAT
Sample_Name XYZ_X XYZ_Y XYZ_Z Lab_L Lab_a Lab_b
END_DATA_FORMAT
BEGIN_DATA
A1 11.48 9.88 4.67 37.63 14.85 15.64
A2 39.11 30.25 4.12 61.87 34.51 60.58
A3 7.30 5.73 23.07 28.72 18.78 -53.73
A4 86.77 90.01 74.18 96.00 0.01 0.00
B1 39.66 35.93 19.88 66.47 16.39 17.68
B2 12.13 11.22 27.98 39.95 9.40 -43.06
B3 14.79 23.12 7.34 55.20 -39.20 33.44
B4 56.98 59.11 48.71 81.35 0.00 0.00
C1 17.02 18.60 25.88 50.22 -4.91 -21.76
C2 30.16 19.82 10.24 51.63 47.92 16.81
C3 22.04 12.40 3.70 41.84 56.41 28.65
C4 34.90 36.20 29.83 66.67 0.02 0.01
D1 10.79 13.30 5.37 43.21 -14.26 21.61
D2 8.59 6.59 10.93 30.85 21.37 -21.21
D3 59.45 59.69 7.70 81.67 4.61 77.64
D4 19.09 19.80 16.32 51.61 0.02 0.00
E1 24.60 23.40 33.67 55.48 9.04 -25.16
E2 35.14 43.91 8.73 72.17 -22.85 57.39
E3 30.63 19.70 22.50 51.50 50.26 -13.37
E4 8.68 9.00 7.42 35.98 0.04 -0.01
F1 30.82 41.85 34.83 70.77 -32.13 -0.49
F2 49.94 44.85 6.32 72.79 18.87 68.12
F3 13.04 18.38 29.81 49.95 -27.61 -28.80
F4 2.99 3.10 2.55 20.44 0.03 0.04
END_DATA
The patch measurements follow the BEGIN_DATA line and are presented as seven items per row. The first is the identifier indicating the column (A through F) and the row (1 through 4). The next three items are numbers representing the XYZ values for the patch (relative to the CIE 2° standard observer and the CIE D50 reference illuminant). The last three items are the numbers representing the CIE Lab values for the color. For example, the ColorChecker "White" patch (lower left corner of the chart) has the identifier of A4 (first column, fourth row), XYZ value of (86.77, 90.01, 74.18) and Lab value of (96.00, 0.01, 0.00).
The contents of ColorChecker 24.txt are shown here:
LGOROWLENGTH 4
CREATED "2/5/2004" # Time: 18:16
INSTRUMENTATION "Unknown"
MEASUREMENT_SOURCE "Illumination=Unknown ObserverAngle=Unknown WhiteBase=Abs Filter=Unknown"
ILLUMINATION_NAME "D50"
OBSERVER_ANGLE "2"
KEYWORD "SampleID"
KEYWORD "SAMPLE_NAME"
NUMBER_OF_FIELDS 38
BEGIN_DATA_FORMAT
SampleID SAMPLE_NAME nm380 nm390 nm400 nm410 nm420 nm430 nm440 nm450 nm460 nm470 nm480 nm490 nm500 nm510 nm520 nm530 nm540 nm550 nm560 nm570 nm580 nm590 nm600 nm610 nm620 nm630 nm640 nm650 nm660 nm670 nm680 nm690 nm700 nm710 nm720 nm730
END_DATA_FORMAT
NUMBER_OF_SETS 24
BEGIN_DATA
1 A1 0.0479 0.0553 0.0610 0.0626 0.0619 0.0616 0.0614 0.0615 0.0618 0.0619 0.0618 0.0622 0.0638 0.0696 0.0767 0.0801 0.0817 0.0845 0.0902 0.1017 0.1175 0.1336 0.1435 0.1479 0.1514 0.1580 0.1675 0.1772 0.1842 0.1853 0.1811 0.1765 0.1773 0.1834 0.1914 0.2018
2 A2 0.0520 0.0540 0.0530 0.0534 0.0529 0.0528 0.0532 0.0542 0.0557 0.0573 0.0597 0.0628 0.0683 0.0902 0.1268 0.1559 0.1730 0.1944 0.2424 0.3329 0.4517 0.5525 0.5952 0.5982 0.5942 0.5922 0.5932 0.5944 0.6032 0.6178 0.6389 0.6607 0.6791 0.6886 0.6871 0.6901
3 A3 0.0511 0.0605 0.0779 0.1280 0.1986 0.2481 0.2830 0.3058 0.3006 0.2716 0.2291 0.1813 0.1349 0.0962 0.0710 0.0536 0.0440 0.0396 0.0376 0.0371 0.0371 0.0374 0.0376 0.0381 0.0386 0.0391 0.0399 0.0406 0.0420 0.0428 0.0429 0.0431 0.0448 0.0481 0.0529 0.0607
4 A4 0.1267 0.2179 0.4164 0.6780 0.8397 0.8911 0.9035 0.9092 0.9154 0.9180 0.9194 0.9225 0.9209 0.9212 0.9242 0.9227 0.9238 0.9248 0.9227 0.9252 0.9233 0.9242 0.9239 0.9239 0.9242 0.9237 0.9264 0.9288 0.9308 0.9284 0.9276 0.9284 0.9304 0.9328 0.9328 0.9345
5 B1 0.0962 0.1328 0.1706 0.1877 0.1903 0.1923 0.1971 0.2064 0.2245 0.2535 0.2922 0.3274 0.3473 0.3489 0.3224 0.2835 0.2671 0.2728 0.2741 0.2836 0.3334 0.4183 0.4950 0.5409 0.5625 0.5731 0.5820 0.5902 0.6025 0.6174 0.6375 0.6626 0.6910 0.7171 0.7339 0.7475
6 B2 0.0988 0.1506 0.2227 0.2834 0.3316 0.3701 0.3999 0.4146 0.4075 0.3781 0.3280 0.2680 0.2112 0.1660 0.1366 0.1162 0.1041 0.0961 0.0898 0.0858 0.0837 0.0836 0.0837 0.0832 0.0830 0.0840 0.0879 0.0952 0.1057 0.1202 0.1413 0.1721 0.2147 0.2685 0.3284 0.3915
7 B3 0.0531 0.0559 0.0566 0.0576 0.0575 0.0586 0.0606 0.0652 0.0745 0.0932 0.1270 0.1771 0.2424 0.3154 0.3470 0.3392 0.3213 0.2964 0.2612 0.2271 0.1962 0.1667 0.1386 0.1182 0.1066 0.1003 0.0971 0.0950 0.0950 0.0973 0.1014 0.1075 0.1137 0.1176 0.1173 0.1173
8 B4 0.1166 0.1987 0.3599 0.5193 0.5784 0.5910 0.5960 0.5988 0.6002 0.5984 0.5965 0.5966 0.5947 0.5954 0.5987 0.5983 0.5985 0.5978 0.5958 0.5970 0.5951 0.5942 0.5926 0.5908 0.5888 0.5857 0.5847 0.5831 0.5831 0.5811 0.5786 0.5762 0.5749 0.5742 0.5723 0.5711
9 C1 0.1053 0.1633 0.2518 0.3163 0.3325 0.3355 0.3349 0.3294 0.3199 0.3055 0.2863 0.2737 0.2612 0.2378 0.2199 0.2173 0.2118 0.1884 0.1682 0.1639 0.1613 0.1550 0.1458 0.1375 0.1327 0.1305 0.1302 0.1322 0.1362 0.1372 0.1340 0.1288 0.1227 0.1187 0.1205 0.1303
10 C2 0.0865 0.1099 0.1303 0.1352 0.1332 0.1310 0.1294 0.1275 0.1244 0.1194 0.1136 0.1083 0.1027 0.0974 0.0936 0.0914 0.0912 0.0915 0.0934 0.1044 0.1510 0.2590 0.3925 0.4963 0.5528 0.5766 0.5863 0.5896 0.5919 0.5905 0.5881 0.5868 0.5890 0.5923 0.5944 0.5965
11 C3 0.0478 0.0474 0.0470 0.0461 0.0459 0.0453 0.0449 0.0447 0.0445 0.0437 0.0427 0.0421 0.0417 0.0412 0.0412 0.0413 0.0416 0.0426 0.0446 0.0491 0.0607 0.0939 0.1812 0.3323 0.4816 0.5800 0.6317 0.6577 0.6728 0.6793 0.6847 0.6909 0.6980 0.7046 0.7084 0.7129
12 C4 0.1074 0.1704 0.2705 0.3409 0.3601 0.3655 0.3698 0.3724 0.3733 0.3715 0.3692 0.3689 0.3673 0.3684 0.3711 0.3714 0.3714 0.3707 0.3694 0.3703 0.3692 0.3685 0.3669 0.3647 0.3625 0.3596 0.3579 0.3560 0.3548 0.3526 0.3500 0.3475 0.3460 0.3444 0.3421 0.3403
13 D1 0.0477 0.0507 0.0527 0.0537 0.0544 0.0563 0.0584 0.0601 0.0611 0.0619 0.0634 0.0659 0.0721 0.0958 0.1386 0.1748 0.1855 0.1742 0.1529 0.1351 0.1239 0.1171 0.1106 0.1048 0.1022 0.1030 0.1052 0.1068 0.1073 0.1060 0.1035 0.1021 0.1034 0.1069 0.1104 0.1150
14 D2 0.0854 0.1240 0.1696 0.1955 0.1970 0.1849 0.1651 0.1430 0.1213 0.1020 0.0868 0.0750 0.0655 0.0599 0.0567 0.0533 0.0517 0.0519 0.0526 0.0524 0.0516 0.0529 0.0591 0.0732 0.0924 0.1117 0.1327 0.1610 0.1981 0.2365 0.2698 0.2953 0.3090 0.3161 0.3314 0.3694
15 D3 0.0476 0.0488 0.0496 0.0499 0.0496 0.0506 0.0526 0.0567 0.0652 0.0813 0.1110 0.1556 0.2211 0.3353 0.4692 0.5703 0.6249 0.6551 0.6783 0.7018 0.7171 0.7290 0.7367 0.7423 0.7471 0.7508 0.7558 0.7598 0.7647 0.7661 0.7693 0.7746 0.7814 0.7876 0.7902 0.7938
16 D4 0.0912 0.1253 0.1599 0.1778 0.1820 0.1853 0.1886 0.1904 0.1903 0.1884 0.1869 0.1866 0.1856 0.1864 0.1883 0.1886 0.1885 0.1880 0.1867 0.1867 0.1855 0.1846 0.1829 0.1811 0.1789 0.1768 0.1752 0.1733 0.1719 0.1702 0.1681 0.1662 0.1651 0.1636 0.1623 0.1612
17 E1 0.1092 0.1802 0.2996 0.3941 0.4244 0.4329 0.4357 0.4336 0.4247 0.4070 0.3817 0.3492 0.3113 0.2787 0.2532 0.2293 0.2163 0.2114 0.2049 0.1986 0.1959 0.2025 0.2173 0.2325 0.2412 0.2508 0.2722 0.3030 0.3343 0.3507 0.3486 0.3406 0.3397 0.3468 0.3584 0.3764
18 E2 0.0556 0.0605 0.0646 0.0653 0.0661 0.0676 0.0708 0.0765 0.0867 0.1044 0.1344 0.1818 0.2574 0.3757 0.4837 0.5446 0.5636 0.5579 0.5381 0.5135 0.4783 0.4356 0.3891 0.3529 0.3320 0.3211 0.3149 0.3108 0.3137 0.3248 0.3422 0.3613 0.3772 0.3847 0.3829 0.3847
19 E3 0.1112 0.1763 0.2824 0.3552 0.3693 0.3612 0.3407 0.3130 0.2832 0.2539 0.2230 0.1935 0.1700 0.1499 0.1288 0.1088 0.1014 0.1038 0.1043 0.1085 0.1364 0.2037 0.3027 0.4147 0.5219 0.6124 0.6785 0.7232 0.7550 0.7707 0.7766 0.7790 0.7815 0.7854 0.7937 0.8114
20 E4 0.0657 0.0764 0.0858 0.0898 0.0911 0.0918 0.0929 0.0933 0.0927 0.0918 0.0910 0.0906 0.0898 0.0898 0.0905 0.0904 0.0904 0.0901 0.0899 0.0902 0.0902 0.0902 0.0894 0.0888 0.0880 0.0869 0.0864 0.0859 0.0851 0.0843 0.0833 0.0824 0.0818 0.0818 0.0815 0.0815
21 F1 0.1095 0.1696 0.2524 0.3074 0.3279 0.3427 0.3592 0.3839 0.4231 0.4733 0.5243 0.5676 0.5908 0.5959 0.5870 0.5648 0.5338 0.4915 0.4413 0.3952 0.3511 0.3059 0.2621 0.2319 0.2158 0.2074 0.2025 0.1991 0.2009 0.2086 0.2198 0.2305 0.2386 0.2400 0.2352 0.2346
22 F2 0.0544 0.0604 0.0627 0.0637 0.0638 0.0638 0.0646 0.0655 0.0668 0.0680 0.0696 0.0725 0.0813 0.1221 0.2118 0.3215 0.4017 0.4442 0.4735 0.5120 0.5562 0.5988 0.6283 0.6450 0.6538 0.6586 0.6641 0.6692 0.6749 0.6773 0.6813 0.6868 0.6934 0.6997 0.7034 0.7077
23 F3 0.0813 0.1282 0.1940 0.2456 0.2693 0.2921 0.3237 0.3611 0.4029 0.4439 0.4654 0.4621 0.4342 0.3895 0.3417 0.2903 0.2404 0.1929 0.1510 0.1226 0.1049 0.0936 0.0844 0.0776 0.0742 0.0724 0.0722 0.0732 0.0757 0.0768 0.0759 0.0736 0.0710 0.0696 0.0718 0.0793
24 F4 0.0286 0.0290 0.0297 0.0305 0.0312 0.0310 0.0314 0.0315 0.0316 0.0315 0.0315 0.0313 0.0309 0.0310 0.0313 0.0313 0.0311 0.0310 0.0309 0.0310 0.0307 0.0305 0.0302 0.0300 0.0300 0.0303 0.0303 0.0304 0.0308 0.0308 0.0309 0.0309 0.0310 0.0311 0.0312 0.0316
END_DATA
The patch measurements follow the BEGIN_DATA line, one per line. Each line begins with the data line number, followed by an identifier indicating the column (A through F) and the row (1 through 4), which is followed by the spectral measurement data for the patch. Each measurement consists of 36 numbers, which represent the spectral responses from 380 through 730 nm at 10 nm intervals.
Your measuring instrument may have come with software that can create a file in one of these formats. If not, the easiest way to make a custom reference file that can be used with inCamera, is to copy the file that is included with inCamera, and then edit it with any text editor that can save plain (unformatted) text files.
You will notice that your ColorChecker chart comes with a printed data sheet containing color information about the chart. Please note that the chromaticity coordinates (x, y) for the colors are provided relative to the CIE standard C illuminant, while ICC profiles and Adobe Photoshop both use CIE standard D50 illuminant. This means you cannot use the printed values without first accounting for the reference illuminant difference. Furthermore, the data sheet also contains RGB values for the patches. These values are completely meaningless and should not be used for any purpose whatever.
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