RGB Coordinates of the Macbeth ColorChecker-已解密.pdf-资料库

RGB coordinates of the Macbeth ColorChecker Danny Pascale The BabelColor Company dpascale@BabelColor.com www.BabelColor.com © 2000-2006 Danny Pascale Abstract. The ColorChecker chart, manufactured by GretagMacbeth, is commonly used as a reference target for photographic and video production work. This document provides RGB coordinates, in 8-bit and 16-bit formats, for all color patches in four common RGB spaces (Adobe, Apple, ProPhoto, and sRGB), which are defined in terms of primaries, Illuminant, and gamma response. The method and equations used to derive the data are presented as well. Reference data provided by the chart’s manufacturer is compared to user-measured values. Subject terms: ColorChecker, RGB coordinates, RGB space, color space, color conversion. Complete update June 1st, 2006 RGB and ProPhoto, are not given. This paper’s purpose is to provide numbers for these spaces, in both 8 bits per primary (24 bits for R’G’B’) and 16 bits per primary formats (48 bits for R’G’B’), as well as present the method by which they were derived. These coordinates should be used in any program where specific “RGB” values can be assigned. Please notice the absence of primes against the letters of “RGB” in the preceding sentence, which reflect how gamma corrected coordinates are referred to in most software, even if R’G’B’ is the correct form (albeit more cumbersome to write). However, obtaining R’G’B’ data is not enough for many chart users who want to know how representative these numbers are, and how close these numbers are to the ones of their chart. Also, inquisitive users may be interested in how the new numbers compare with the old ones. This is the subject of Section 2. The R’G’B’ values derived from the new reference data are presented in Section 3, as well as the R’G’B’ values derived from the BabelColor average. Section 4 presents a short description of each space. The process by which the values were obtained follows, in Section 5. The process can be used for spaces not covered by this paper; for example, for a space defined for a particular display with color primaries different from the ones presented here. 2. Comparing ColorChecker references We have gathered four data sets which we consider reliable enough to be used as references: i) ColorChecker 1976: xyY data with Illuminant C (Ref. 2) ii) ColorChecker 2005: L*a*b* D50 and sRGB (Ref. 4) iii) BabelColor Avg.: spectral data (Ref. 3) iv) ProfileMaker 2004: spectral data (2/5/2004) Other measurements were found, in either tristimulus or spectral form, but they were either incomplete (no data for all patches), or they were from a single chart, or their origin could not be confirmed. We know that, some time ago, L*a*b* D50 data was available from the Munsell Web site, but the file was removed when the Web site was updated. Introduction 1. The ColorChecker1 chart is ubiquitous in the photographic and video fields. Its main application is for obtaining a rapid assessment of an imaging devices’ color rendering accuracy, although it can also be used for simple calibration purposes. The chart consists of 24 color patches formulated to emulate common natural colors such as skin colors, foliage, and sky, in addition to additive and subtractive primaries, and a six steps gray scale2. While designed for optimum color consistency when comparing pictures of the chart with pictures of the natural colors, as reproduced on color film, it was shown that the degree of metamerism was also very small when directly comparing the chart to the natural colors. Until recently, R’G’B’ values for this chart were difficult to find. In particular, the R’G’B’ data supplied with the chart corresponded to no common RGB space, and no primaries and white point coordinates were provided either. The only official and reliable tristimulus data supplied with the product consisted of xyY coordinates measured with CIE Illuminant C, a common Daylight Illuminant when the original data was measured (from Ref. 2); this data was used, by this author, as a basis to determine R’G’B’ values, and published in a previous version of this document. In view of this limited information, the author started, a few years ago, to compile and average spectral data measured on ColorCheckers by users from all over the world. This “real-life” data, from 20 charts of various ages (all of them in well kept conditions), and measured using various instruments, can be seen as an independent validation of the official reference data. This average data, labeled “BabelColor Avg.” throughout this text, was used to derive R’G’B’ values for comparison purposes. Extracts of the data set are presented here; the complete data is available in a spreadsheet which can be downloaded from the BabelColor Web site3. Since about October 2005, the GretagMacbeth Company provides sRGB values, in 8-bit format, and L*a*b* D50 data with its standard size and Mini format ColorChecker charts; the data is also freely accessible on their Web site4. The published data is the same for both charts. However, R’G’B’ data for other popular spaces, such as Adobe RGB, Apple

2 Table 1a Color name No. dark skin 1 light skin 2 blue sky 3 foliage 4 blue flower 5 bluish green 6 orange 7 purplish blue 8 9 moderate red 10 11 12 13 14 15 16 17 magenta 18 19 white 9.5 (.05 D) neutral 8 (.23 D) 20 neutral 6.5 (.44 D) 21 neutral 5 (.70 D) 22 neutral 3.5 (1.05 D) 23 black 2 (1.5 D) 24 purple yellow green orange yellow blue green red yellow cyan ColorChecker 2005 b* L* 37,99 14,06 17,81 65,71 -21,93 49,93 21,91 43,14 -25,40 55,11 70,72 -0,199 57,10 62,66 -45,96 40,02 16,25 51,12 30,33 -21,59 57,26 72,53 67,86 71,94 -50,30 28,78 55,26 31,37 28,19 42,10 79,82 81,73 -14,57 51,94 51,04 -28,64 1,186 96,54 -0,335 81,26 -0,504 66,77 50,87 -0,270 -1,231 35,66 20,46 -0,973 a* 13,56 18,13 -4,88 -13,10 8,84 -33,40 36,07 10,41 48,24 22,98 -23,71 19,36 14,18 -38,34 53,38 4,04 49,99 -28,63 -0,425 -0,638 -0,734 -0,153 -0,421 -0,079 Table 1b Color name No. dark skin 1 light skin 2 blue sky 3 foliage 4 blue flower 5 bluish green 6 orange 7 purplish blue 8 9 moderate red 10 11 12 13 14 15 16 17 magenta 18 19 white 9.5 (.05 D) neutral 8 (.23 D) 20 neutral 6.5 (.44 D) 21 neutral 5 (.70 D) 22 neutral 3.5 (1.05 D) 23 black 2 (1.5 D) 24 purple yellow green orange yellow blue green red yellow cyan ColorChecker 2005 b* L* 14,06 37,99 17,81 65,71 49,93 -21,93 21,91 43,14 -25,40 55,11 -0,199 70,72 62,66 57,10 -45,96 40,02 16,25 51,12 -21,59 30,33 57,26 72,53 71,94 67,86 -50,30 28,78 31,37 55,26 28,19 42,10 81,73 79,82 -14,57 51,94 -28,64 51,04 1,186 96,54 -0,335 81,26 66,77 -0,504 -0,270 50,87 -1,231 35,66 20,46 -0,973 a* 13,56 18,13 -4,88 -13,10 8,84 -33,40 36,07 10,41 48,24 22,98 -23,71 19,36 14,18 -38,34 53,38 4,04 49,99 -28,63 -0,425 -0,638 -0,734 -0,153 -0,421 -0,079 ColorChecker 1976 b* L* 38,14 14,75 17,30 66,63 -22,43 50,73 21,85 43,36 -25,74 56,01 71,50 0,831 58,56 62,28 -44,07 40,44 15,56 51,94 30,50 -23,65 58,64 72,83 66,70 72,18 -52,83 28,59 55,66 33,09 26,98 41,71 78,47 81,95 -15,57 51,57 51,07 -27,36 0,067 96,00 0,058 81,35 0,049 66,67 51,58 0,040 0,031 35,99 0,022 20,56 avg. : a* 13,81 15,38 -3,15 -14,99 9,63 -31,93 31,88 11,42 45,25 23,99 -23,76 17,40 20,31 -38,77 53,43 1,65 48,99 -28,01 -0,062 -0,054 -0,046 -0,037 -0,029 -0,020 L* 38,36 66,06 50,09 43,20 55,36 70,70 62,56 40,18 51,71 30,38 72,49 71,96 28,65 55,05 42,18 82,23 51,82 50,55 96,39 81,01 66,30 50,83 35,72 20,71 BabelColor Avg. b* 14,65 17,85 -22,51 21,73 -24,82 -0,240 58,05 -44,29 16,86 -20,31 57,08 68,00 -50,52 31,62 28,79 79,84 -13,90 -28,14 2,238 0,180 -0,079 -0,268 -0,468 -0,447 avg. : a* 13,80 17,74 -4,41 -13,46 8,89 -32,89 35,13 9,55 47,69 21,13 -23,46 19,49 15,60 -38,09 54,89 4,05 49,79 -27,97 -0,404 -0,570 -0,434 -0,687 -0,521 0,025 2006-06-01 ΔE ΔE ≤ 1 1 < ΔE ≤ 2 2 < ΔE ≤ 4 4 < ΔE ΔE CIELAB DE2000 0,45 2,01 1,75 1,32 0,98 1,09 2,72 1,61 1,26 1,06 0,48 1,08 3,11 0,77 0,73 1,40 0,72 0,54 1,25 0,94 1,14 0,79 1,38 0,98 1,23 0,75 2,95 1,98 1,91 1,24 1,95 4,45 2,19 3,17 2,30 1,41 2,29 6,63 1,82 1,27 2,75 1,46 1,42 1,29 0,71 0,89 0,78 1,36 1,00 2,00 ΔE CIELAB DE2000 0,74 0,52 0,77 0,41 0,63 0,51 1,34 1,89 1,01 2,24 0,31 0,19 1,44 0,41 1,63 0,50 0,71 0,96 1,06 0,57 0,70 0,54 0,77 0,59 0,85 0,49 0,40 0,50 0,31 0,46 0,21 0,80 0,39 0,73 0,97 0,11 0,07 0,88 0,27 0,45 0,34 0,32 0,57 0,98 0,54 0,71 0,78 0,75 0,56 0,52 Table 1a: Official L*a*b* D50 values of the ColorChecker, as made available by GretagMacbeth in 2005 (“ColorChecker 2005”), compared to the previously distributed data measured in 1976 (“ColorChecker 1976”). The 1976 data, measured with Illuminant C, was converted to Illuminant D50 using a Bradford chromatic adaptation transform. Table 1b: “ColorChecker 2005” data compared to L*a*b* D50 data derived from the average of 20 charts compiled by BabelColor (“BabelColor Avg.”).

2006-06-01 Table 1c Color name No. dark skin 1 light skin 2 blue sky 3 foliage 4 blue flower 5 bluish green 6 orange 7 purplish blue 8 9 moderate red 10 11 12 13 14 15 16 17 magenta 18 19 white 9.5 (.05 D) neutral 8 (.23 D) 20 neutral 6.5 (.44 D) 21 neutral 5 (.70 D) 22 neutral 3.5 (1.05 D) 23 black 2 (1.5 D) 24 purple yellow green orange yellow blue green red yellow cyan ColorChecker 2005 b* L* 37,99 14,06 17,81 65,71 -21,93 49,93 21,91 43,14 -25,40 55,11 70,72 -0,199 57,10 62,66 -45,96 40,02 16,25 51,12 30,33 -21,59 57,26 72,53 67,86 71,94 -50,30 28,78 55,26 31,37 28,19 42,10 79,82 81,73 -14,57 51,94 51,04 -28,64 1,186 96,54 -0,335 81,26 -0,504 66,77 50,87 -0,270 -1,231 35,66 20,46 -0,973 a* 13,56 18,13 -4,88 -13,10 8,84 -33,40 36,07 10,41 48,24 22,98 -23,71 19,36 14,18 -38,34 53,38 4,04 49,99 -28,63 -0,425 -0,638 -0,734 -0,153 -0,421 -0,079 Table 1d Color name No. dark skin 1 light skin 2 blue sky 3 foliage 4 blue flower 5 bluish green 6 orange 7 purplish blue 8 9 moderate red 10 11 12 13 14 15 16 17 magenta 18 19 white 9.5 (.05 D) neutral 8 (.23 D) 20 neutral 6.5 (.44 D) 21 neutral 5 (.70 D) 22 neutral 3.5 (1.05 D) 23 black 2 (1.5 D) 24 purple yellow green orange yellow blue green red yellow cyan BabelColor Avg. b* 14,65 17,85 -22,51 21,73 -24,82 -0,240 58,05 -44,29 16,86 -20,31 57,08 68,00 -50,52 31,62 28,79 79,84 -13,90 -28,14 2,238 0,180 -0,079 -0,268 -0,468 -0,447 a* 13,80 17,74 -4,41 -13,46 8,89 -32,89 35,13 9,55 47,69 21,13 -23,46 19,49 15,60 -38,09 54,89 4,05 49,79 -27,97 -0,404 -0,570 -0,434 -0,687 -0,521 0,025 L* 38,36 66,06 50,09 43,20 55,36 70,70 62,56 40,18 51,71 30,38 72,49 71,96 28,65 55,05 42,18 82,23 51,82 50,55 96,39 81,01 66,30 50,83 35,72 20,71 ProfileMaker 2004 b* L* 38,40 14,52 18,22 66,07 -21,70 50,17 22,67 43,27 -25,14 55,47 71,23 -0,060 58,29 62,83 -45,87 40,27 16,56 51,26 30,47 -21,28 57,89 72,95 68,94 72,27 -50,02 28,71 55,40 32,01 28,41 41,50 80,85 82,56 -14,30 52,20 51,37 -28,29 1,470 96,96 0,097 81,57 -0,083 67,17 50,15 -0,490 -0,741 35,94 -0,365 20,38 avg. : a* 13,58 18,02 -4,91 -13,33 8,84 -33,03 35,88 10,39 48,01 21,07 -23,45 19,25 14,36 -38,02 56,42 3,49 49,90 -28,48 -0,474 -0,703 -0,779 -1,225 -0,336 -0,360 ProfileMaker 2004 b* L* 14,52 38,40 18,22 66,07 50,17 -21,70 22,67 43,27 -25,14 55,47 -0,060 71,23 62,83 58,29 -45,87 40,27 16,56 51,26 -21,28 30,47 57,89 72,95 72,27 68,94 -50,02 28,71 32,01 55,40 28,41 41,50 82,56 80,85 -14,30 52,20 -28,29 51,37 1,470 96,96 0,097 81,57 67,17 -0,083 -0,490 50,15 -0,741 35,94 -0,365 20,38 avg. : a* 13,58 18,02 -4,91 -13,33 8,84 -33,03 35,88 10,39 48,01 21,07 -23,45 19,25 14,36 -38,02 56,42 3,49 49,90 -28,48 -0,474 -0,703 -0,779 -1,225 -0,336 -0,360 3 ΔE ΔE ≤ 1 1 < ΔE ≤ 2 2 < ΔE ≤ 4 4 < ΔE ΔE CIELAB DE2000 0,47 0,43 0,27 0,40 0,38 0,43 0,55 0,23 0,26 1,03 0,43 0,42 0,25 0,37 1,14 0,69 0,29 0,36 0,37 0,49 0,53 1,71 0,54 0,73 0,53 0,62 0,56 0,33 0,81 0,45 0,65 1,22 0,27 0,41 1,94 0,80 1,14 0,34 0,73 3,11 1,43 0,39 0,51 0,51 0,54 0,58 1,31 0,58 0,68 0,83 ΔE CIELAB DE2000 0,26 0,47 0,95 0,95 0,34 0,58 0,83 1,79 0,62 0,98 0,93 1,02 1,33 0,53 1,72 1,20 0,56 0,97 0,96 0,58 0,94 0,89 0,40 0,51 0,85 0,17 0,23 0,55 0,55 0,26 0,43 0,41 0,35 0,50 0,61 0,43 0,43 0,65 0,38 0,90 0,47 0,41 0,85 0,80 0,44 0,86 1,04 0,42 0,62 0,53 Table 1c: Official L*a*b* D50 values of the ColorChecker, as made available by GretagMacbeth in 2005 (“ColorChecker 2005”), compared to values derived from the reference spectral file provided with ProfileMaker (“ProfileMaker 2004”; Table 1d: L*a*b* D50 data derived from the average of 20 charts compiled by BabelColor (“BabelColor Avg.”), file name: “ColorChecker 24”; file measurement date: “2/5/2004”). compared to “ProfileMaker 2004”.

4 2006-06-01 The first comparison that comes to mind is the one between the two “official” tristimulus data sets, published in 1976 (“ColorChecker 1976”) and 2005 (“ColorChecker 2005”), shown in Table 1a. In order to compare the two sets on the same basis, we have chosen to convert the xyY Ill-C (1976) coordinates to the L*a*b* D50 color space used for the most recent reference. From xyY, one can readily determine XYZ values, then use a Chromatic Adaptation Transform (CAT), in this case the Bradford matrix discussed in Section 5.2, to convert the XYZ coordinates between Illuminant C and Illuminant D50, and finally compute the proper L*a*b* values. The use of a CAT is required since we do not have the spectral data corresponding to the xyY coordinates. While using a CAT can introduce an error, this error has less of an effect than if it was simply added to the inherent difference between the data sets; see Section 6 for more information. third comparison, Table 1c, The second comparison, shown in Table 1b, is between the “ColorChecker 2005” data set and the “BabelColor Avg.”. The the “ColorChecker 2005” set and tristimulus data derived from a spectral reference file of the ColorChecker (ProfileMaker 2004). This file is provided by GretagMacbeth as part of their ProfileMaker software package; the measurement date shown in the file is “2/5/2004”. The fourth comparison, Table 1d, is between the “BabelColor Avg.” and “ProfileMaker 2004” data sets. is between The color differences in Table 1 are computed using both CIELAB and CIEDE2000. CIEDE2000 is the most recent color difference formula recommended by the Commission Internationale de l'Éclairage (CIE). Like the CIE94 and CMC color difference formulas which came after CIELAB, it strives to improve the match between the perceived color difference and the computed difference values. CIEDE2000, similarly to the CIE94 and CMC formulas, includes weighting functions for it introduces an extra term which combines chroma and hue with the goal of improving the performance for blue colors (for hue angles – the h* in the L*C*h* presentation format – around 275 degrees). It also associates a scaling factor to a* for low chroma colors, to improve the formula performance near the illuminant. Many users have confirmed that CIEDE2000, while still not perfect, does achieve its goal of improving the match between computed difference numbers and perceived difference5. lightness, chroma and hue. However, In Table 1a, we see a noticeable difference between the “ColorChecker 1976” and “ColorChecker 2005” data sets, whereas the difference is quite small when comparing the 2005 data with either the “BabelColor Avg.” or the “ProfileMaker 2004” sets in Tables 1b and 1c. The 1976 data may have been deemed sufficiently precise at a time where the chart was mostly used to visually judge the quality of silver- based to make precise digital measurements as we do now. films, and not used As per GretagMacbeth Web site, the 2005 ColorChecker data “is intended to be an average measurement of all ColorChecker Charts”. The fact that, on average, this data set cannot be visually differentiated from either the “ProfileMaker 2004” or the “BabelColor Avg.” data sets makes it difficult to select the best one. There is no detailed information on where the 2005 data comes from; it may be an average from one, or from many production lots. There is even less information on the origin of the ProfileMaker reference file but its good match to the other data sets indicates it is also an average of some sorts. As for the data compiled by BabelColor, the match to the other two data sets is quite good, especially considering the mix of experimental conditions imposed by many users using different instruments. Overall, the similarity of the three data sets points to some outstanding long term production consistency. Readers interested in seeing spectral graphs for each patch, as well as information on spectral and L*a*b* variance, can download “ColorChecker_RGB_and_spectra.xls” spreadsheet from the BabelColor Web site (see Ref. 3). the 3. RGB coordinates of the ColorChecker The R’G’B’ values of the ColorChecker for four common RGB spaces, Adobe, Apple, ProPhoto and sRGB, are shown in 8-bit format in Table 2, and in 16-bit format in Table 3. Table 3 is a more precise version of Table 2, with more significant digits per value. The 16-bit values can be used mainly in programming environments, such as MATLAB, since there is no color picker that yet offers 16-bit resolution. You should be aware that, for computing efficiency reasons, Photoshop processes 16-bit file as if 15-bit and resaves the file as 16-bit; the displayed color numbers are thus divided by two from the 16-bit values. In Tables 2 and 3, the tables labeled “ColorChecker 2005” show the L*a*b* D50 values provided by GretagMacbeth. You will notice two columns with sRGB in their title in Table 2; the one labeled “sRGB (GMB)” contains the values provided by GretagMacbeth, while the “sRGB” column was derived from L*a*b* D50 using the procedure presented in Section 5. The other R’G’B’ values of the “ColorChecker 2005” table were derived in a similar manner. It should be emphasized that for ProPhoto, a D50 based RGB space, there is no need to perform a chromatic adaptation transform when starting with L*a*b* D50 and that there is minimal “conversion process-induced” errors (see Section 6). All R’G’B’ values of the “BabelColor Avg.” tables were obtained with the spectral reflectance average of 20 charts, the space Illuminant spectral distribution, and the 2-degrees Standard Observer. In other words, they were not obtained using a chromatic adaptation transform, and do not comprise the errors this transform may introduce. It is interesting to note in Table 2 that the “sRGB (GMB)” cyan patch is measured to be within the sRGB gamut, with an R’ value of 8, while this coordinate is clipped to zero when derived from the L*a*b* data (as can be seen in the “sRGB” column of the “ColorChecker 2005” table). The cyan is similarly clipped in the “BabelColor Avg.” tables.

2006-06-01 ColorChecker 2005 No. Color name illuminant 0 dark skin 1 light skin 2 blue sky 3 foliage 4 blue flower 5 bluish green 6 orange 7 purplish blue 8 9 moderate red purple 10 yellow green 11 orange yellow 12 blue 13 green 14 red 15 yellow 16 17 magenta cyan 18 19 white 9.5 (.05 D) neutral 8 (.23 D) 20 neutral 6.5 (.44 D) 21 neutral 5 (.70 D) 22 neutral 3.5 (1.05 D) 23 black 2 (1.5 D) 24 BabelColor Avg. Color name No. illuminant 0 dark skin 1 light skin 2 blue sky 3 foliage 4 blue flower 5 bluish green 6 orange 7 purplish blue 8 9 moderate red purple 10 yellow green 11 orange yellow 12 blue 13 green 14 red 15 yellow 16 17 magenta cyan 18 19 white 9.5 (.05 D) neutral 8 (.23 D) 20 neutral 6.5 (.44 D) 21 neutral 5 (.70 D) 22 neutral 3.5 (1.05 D) 23 black 2 (1.5 D) 24 5 Apple sRGB ProPhoto Adobe sRGB (GMB) R' G' B' R' G' B' R' G' B' R' G' B' R' G' B' 255 255 68 107 130 184 157 101 67 95 128 177 170 129 44 201 166 77 174 99 108 86 64 167 46 213 150 49 99 73 60 155 31 227 149 169 161 61 245 242 200 200 160 160 121 120 84 85 52 52 255 70 129 153 69 173 171 56 166 97 104 75 55 143 80 59 52 147 167 242 201 162 121 86 54 255 82 150 122 108 128 189 126 91 90 60 188 163 61 148 54 199 86 133 243 200 160 122 85 52 255 115 194 98 87 133 103 214 80 193 94 157 224 56 70 175 231 187 8 243 200 160 122 85 52 255 67 129 156 64 176 172 47 170 97 106 63 39 147 74 57 20 151 170 243 202 163 122 86 51 255 81 147 122 108 128 190 124 91 82 58 189 162 63 149 49 198 84 136 245 202 163 121 84 49 255 116 199 91 90 130 92 224 68 198 94 159 230 35 67 180 238 193 0 245 200 161 121 82 49 255 54 114 133 55 154 157 54 145 80 82 74 60 120 69 46 66 127 148 240 191 146 102 68 38 255 67 135 102 86 111 168 118 74 83 49 170 152 50 123 59 188 85 111 243 190 146 102 66 37 255 81 159 94 75 118 127 167 79 141 68 144 181 57 85 120 199 143 78 242 189 145 102 66 37 255 51 109 139 48 162 155 30 156 79 88 39 19 131 54 43 0 134 154 239 191 146 102 68 38 255 63 128 103 89 108 178 102 71 59 42 177 143 47 133 29 187 60 118 243 191 146 102 66 37 255 94 183 74 73 110 84 211 52 180 73 145 220 26 60 159 232 174 0 242 189 144 101 65 37 255 82 146 122 107 127 188 123 92 83 61 188 160 65 148 52 197 85 135 245 201 161 120 85 53 Apple ProPhoto sRGB Adobe 255 70 129 155 69 173 170 54 164 97 103 75 56 143 78 59 53 147 164 240 199 160 121 85 54 R' G' B' R' G' B' R' G' B' R' G' B' 255 255 67 107 182 129 157 103 65 96 176 129 171 132 197 45 168 79 98 171 105 84 62 168 211 41 147 53 72 101 56 151 22 227 150 165 166 65 240 245 201 199 159 161 121 119 85 84 53 50 255 81 149 123 108 129 191 123 92 84 59 189 161 62 149 48 200 84 136 245 201 161 121 84 50 255 115 196 93 90 130 99 220 72 195 91 160 229 43 71 176 238 188 0 245 200 160 120 83 50 255 54 114 135 56 154 157 52 143 80 81 74 60 120 68 46 67 126 146 237 189 144 102 67 38 255 68 136 102 86 111 168 118 75 85 50 169 152 50 122 59 190 85 109 242 190 144 102 67 37 255 82 160 95 75 119 127 166 79 142 67 144 182 57 85 121 201 143 77 242 189 144 101 66 37 255 51 109 141 48 162 154 29 153 79 87 38 20 131 52 43 0 133 151 236 189 144 102 67 38 255 63 130 103 90 108 179 101 72 62 43 177 142 45 133 29 188 60 118 242 190 144 102 67 37 255 94 180 76 73 110 89 206 55 176 70 147 218 32 63 154 232 168 0 243 188 143 101 66 37 255 82 148 122 108 128 189 122 92 85 61 188 159 64 148 52 198 85 135 245 200 160 121 85 53 xyY (CIE D50) x y xyY (CIE D50) x y Y 100 L*a*b* (CIE D50) b* L* 100 0 0,3585 14,06 0,3777 10,08 37,99 0,3744 34,95 65,71 17,81 -21,93 0,3016 18,36 49,93 0,4499 13,25 43,14 21,91 -25,40 0,2856 23,04 55,11 -0,20 0,3911 41,78 70,72 0,4055 31,18 62,66 57,10 -45,96 0,2106 11,26 40,02 0,3273 19,38 51,12 16,25 -21,59 0,2482 6,37 30,33 57,26 0,5008 44,46 72,53 0,4427 43,57 71,94 67,86 -50,30 0,1692 5,75 28,78 0,5032 23,18 55,26 31,37 28,19 0,3303 12,57 42,10 0,4734 59,81 81,73 79,82 -14,57 0,2688 20,09 51,94 -28,64 0,3023 19,30 51,04 0,3608 91,31 96,54 1,19 -0,34 0,3584 58,94 81,26 -0,50 0,3581 36,32 66,77 -0,27 0,3579 19,15 50,87 0,3548 8,83 35,66 -1,23 -0,97 3,11 20,46 0,3537 a* 0 13,56 18,13 -4,88 -13,10 8,84 -33,40 36,07 10,41 48,24 22,98 -23,71 19,36 14,18 -38,34 53,38 4,04 49,99 -28,63 -0,43 -0,64 -0,73 -0,15 -0,42 -0,08 Y 100 L*a*b* (CIE D50) b* L* 0 0,3585 100 14,65 0,3787 10,29 38,36 0,3749 35,40 66,06 17,85 -22,51 0,2996 18,49 50,09 0,4501 13,29 43,20 21,73 -24,82 0,2871 23,28 55,36 -0,24 0,3905 41,75 70,70 0,4081 31,06 62,56 58,05 -44,29 0,2157 11,36 40,18 0,3295 19,89 51,71 16,86 -20,31 0,2544 6,39 30,38 57,08 0,5002 44,40 72,49 0,4426 43,60 71,96 68,00 -50,52 0,1676 5,70 28,65 31,62 0,5040 22,97 55,05 28,79 0,3284 12,62 42,18 0,4730 60,72 82,23 79,84 -13,90 0,2702 19,98 51,82 -28,14 0,3028 18,89 50,55 2,24 0,3625 90,94 96,39 0,18 0,3593 58,50 81,01 0,3588 35,71 66,30 -0,08 -0,27 0,3586 19,12 50,83 -0,47 8,87 35,72 0,3577 0,3562 3,17 20,71 -0,45 a* 0 13,80 17,74 -4,41 -13,46 8,89 -32,89 35,13 9,55 47,69 21,13 -23,46 19,49 15,60 -38,09 54,89 4,05 49,79 -27,97 -0,40 -0,57 -0,43 -0,69 -0,52 0,03 0,3457 0,4316 0,4197 0,2760 0,3703 0,2999 0,2848 0,5295 0,2305 0,5012 0,3319 0,3984 0,4957 0,2018 0,3253 0,5686 0,4697 0,4159 0,2131 0,3469 0,3440 0,3432 0,3446 0,3401 0,3406 0,3457 0,4336 0,4187 0,2757 0,3688 0,3016 0,2856 0,5291 0,2335 0,5002 0,3316 0,3986 0,4960 0,2042 0,3262 0,5734 0,4693 0,4175 0,2146 0,3486 0,3451 0,3447 0,3433 0,3425 0,3436 Table 2: R’G’B’ coordinates of the ColorChecker, in 8-bit format. Coordinates for which clipping occurred are shown with a gray background. Top (“ColorChecker 2005”): The L*a*b* and “sRGB (GMB)” data is from GretagMacbeth; the other values (xyY, Adobe, Apple, ProPhoto and sRGB) were derived from the L*a*b* data using the procedure described in Section 5. Bottom (“BabelColor Avg.”): L*a*b* and R’G’B’ values were derived from the spectral average of 20 charts.

6 ColorChecker 2005 No. Color name illuminant 0 dark skin 1 light skin 2 blue sky 3 foliage 4 blue flower 5 bluish green 6 orange 7 purplish blue 8 9 moderate red 10 11 12 13 14 15 16 17 magenta 18 19 white 9.5 (.05 D) neutral 8 (.23 D) 20 neutral 6.5 (.44 D) 21 neutral 5 (.70 D) 22 neutral 3.5 (1.05 D) 23 black 2 (1.5 D) 24 purple yellow green orange yellow blue green red yellow cyan BabelColor Avg. Color name No. illuminant 0 dark skin 1 light skin 2 blue sky 3 foliage 4 blue flower 5 bluish green 6 orange 7 purplish blue 8 9 moderate red 10 11 12 13 14 15 16 17 magenta 18 19 white 9.5 (.05 D) neutral 8 (.23 D) 20 neutral 6.5 (.44 D) 21 neutral 5 (.70 D) 22 neutral 3.5 (1.05 D) 23 black 2 (1.5 D) 24 purple yellow green orange yellow blue green red yellow cyan a* 0 L*a*b* (CIE D50) b* L* 100 0 37,986 65,711 49,927 43,139 55,112 70,719 62,661 40,020 51,124 30,325 72,532 71,941 28,778 55,261 42,101 81,733 51,935 51,038 96,539 81,257 66,766 50,867 35,656 20,461 13,555 18,130 -4,880 -13,095 8,844 -33,397 36,067 10,410 48,239 22,976 -23,709 19,363 14,179 -38,342 53,378 4,039 49,986 -28,631 -0,425 -0,638 -0,734 -0,153 -0,421 -0,079 14,059 17,810 -21,925 21,905 -25,399 -0,199 57,096 -45,964 16,248 -21,587 57,255 67,857 -50,297 31,370 28,190 79,819 -14,574 -28,638 1,186 -0,335 -0,504 -0,270 -1,231 -0,973 a* 0 L*a*b* (CIE D50) b* L* 100 0 38,358 66,056 50,090 43,204 55,356 70,700 62,559 40,178 51,711 30,375 72,492 71,963 28,653 55,046 42,182 82,230 51,820 50,555 96,387 81,014 66,297 50,830 35,724 20,706 13,802 17,737 -4,407 -13,464 8,891 -32,892 35,135 9,551 47,694 21,131 -23,462 19,486 15,600 -38,088 54,893 4,048 49,787 -27,973 -0,404 -0,570 -0,434 -0,687 -0,521 0,025 14,646 17,848 -22,512 21,730 -24,824 -0,240 58,050 -44,289 16,857 -20,309 57,078 67,998 -50,520 31,617 28,785 79,844 -13,904 -28,139 2,238 0,180 -0,079 -0,268 -0,468 -0,447 Adobe G' 65535 21037 37489 31234 27576 32643 48441 31575 23542 21283 15563 48199 41157 16824 37925 13377 50657 21777 34706 62936 51637 41470 30941 21809 13539 Adobe G' 65535 21170 37930 31323 27679 32793 48634 31443 23623 21847 15754 48202 40883 16411 37972 13259 50936 21730 34708 62839 51454 41102 30992 21851 13647 B' 65535 17932 33025 39364 17662 44447 44028 14313 42751 24831 26707 19356 14181 36877 20582 15245 13301 37827 42920 62298 51689 41576 31029 22201 13841 B' 65535 17940 33063 39736 17760 44393 43737 13962 42180 24990 26485 19192 14408 36835 20042 15090 13593 37690 42055 61577 51238 41054 30991 21954 13795 R' 65535 27426 47379 25919 24528 32927 33187 51626 19711 44624 22093 42816 54654 12591 25519 39846 58361 43542 15780 62890 51294 41082 30850 21522 13424 R' 65535 27427 46858 26357 24611 33111 34033 50616 20328 43878 21538 43111 54237 13494 26024 38918 58390 42397 16727 62871 51214 40921 30704 21631 13618 R' 65535 24272 47061 19061 18814 28179 21635 54315 13412 46277 18775 37223 56662 6744 15499 40882 59657 44678 0 62308 48454 36900 26064 16716 9404 R' 65535 24245 46219 19634 18888 28387 22962 52933 14223 45214 18091 37668 56124 8096 16294 39705 59620 43169 0 62323 48400 36794 25852 16842 9595 Table 3: R’G’B’ coordinates of the ColorChecker, in 16-bit format. Coordinates for which clipping occurred are shown with a gray background. Top (“ColorChecker 2005”): The L*a*b* data is from GretagMacbeth; the R’G’B’values were derived from the L*a*b* data Bottom (“BabelColor Avg.”): L*a*b* and R’G’B’ values were derived from the spectral average of 20 charts. using the procedure described in Section 5. Apple ProPhoto sRGB 2006-06-01 G' 65535 16153 32784 26484 22981 27684 45841 26099 18365 15231 10808 45581 36855 11979 34177 7492 47961 15483 30411 62388 48985 37472 26190 17081 9535 G' 65535 16287 33312 26559 23087 27846 46056 26017 18452 15889 11025 45576 36556 11556 34223 7483 48296 15524 30420 62281 48775 37062 26250 17124 9628 B' 65535 13188 27946 35753 12230 41629 39917 7836 40089 20218 22518 10085 4761 33587 13894 11082 0 34453 39705 61541 49038 37587 26286 17484 9817 B' 65535 13185 27949 36178 12320 41556 39544 7462 39419 20351 22277 9858 5255 33552 13271 10945 0 34301 38682 60612 48492 36998 26240 17226 9768 R' 65535 20795 40907 24175 19249 30315 32629 42868 20351 36263 17495 37022 46640 14563 21842 30812 51240 36857 19993 62217 48688 37161 26131 16932 9502 G' 65535 17235 34660 26096 22117 28442 43161 30308 19117 21340 12667 43576 38989 12920 31642 15251 48436 21856 28496 62346 48923 37407 26179 17053 9531 ProPhoto R' 65535 21065 41088 24358 19220 30507 32731 42582 20337 36595 17247 37047 46688 14720 21764 31163 51670 36739 19852 62107 48512 36885 26002 16963 9628 G' 65535 17418 34953 26172 22181 28596 43109 30346 19254 21774 12835 43524 38992 12758 31474 15087 48849 21803 28125 62194 48708 37024 26198 17093 9630 B' 65535 13942 29175 34288 14249 39678 40445 13797 37271 20465 21146 19080 15365 30946 17800 11935 16899 32665 38002 61675 49018 37556 26268 17412 9770 B' 65535 13958 29396 34655 14334 39609 40449 13468 36662 20603 20734 19115 15334 30949 17600 11809 17164 32307 37418 60977 48565 37019 26243 17205 9743 R' 65535 29684 51033 23285 23061 33299 23760 57637 17444 50970 24062 40800 59221 9090 17200 46236 61244 49611 0 62954 51492 41301 31014 21187 12507 R' 65535 29648 50244 23958 23139 33501 25382 56443 18426 50002 23277 41244 58773 11084 18307 45152 61195 48247 0 62967 51453 41222 30782 21331 12759 G' 65535 20794 37831 31447 27664 32893 48805 31797 23445 21055 14904 48564 41533 16275 38272 12506 50998 21580 35002 63018 51965 41847 31145 21613 12685 sRGB G' 65535 20935 38278 31538 27772 33047 48996 31662 23530 21654 15113 48567 41257 15826 38320 12376 51274 21529 35005 62924 51785 41477 31198 21658 12804 B' 65535 17311 33071 40035 16548 45254 44209 12000 43738 24945 27134 16148 10089 37805 19051 14638 5069 38695 43613 62371 52019 41958 31239 22046 13032 B' 65535 17313 33089 40419 16655 45194 43894 11558 43150 25096 26893 15925 10499 37768 18395 14467 5688 38553 42717 61645 51563 41427 31196 21772 12975 Apple

2006-06-01 7 sRGB from L*a*b* D50 (ColorChecker 2005) sRGB (GMB) (ColorChecker 2005) No. Color name R' G' B' dark skin 1 light skin 2 blue sky 3 foliage 4 blue flower 5 bluish green 6 orange 7 purplish blue 8 9 moderate red 10 11 12 13 14 15 16 17 magenta 18 19 white 9.5 (.05 D) neutral 8 (.23 D) 20 neutral 6.5 (.44 D) 21 neutral 5 (.70 D) 22 neutral 3.5 (1.05 D) 23 black 2 (1.5 D) 24 purple yellow green orange yellow blue green red yellow cyan 81 116 67 199 147 129 122 156 91 90 108 64 130 128 176 190 172 92 47 224 124 68 91 170 97 82 198 106 94 58 63 159 189 39 230 162 35 63 147 74 149 67 57 180 49 20 238 198 193 84 151 0 136 170 245 245 243 200 202 202 161 163 163 121 121 122 86 82 51 49 84 49 R' G' B' 82 98 87 L*a*b* (CIE D65) b* L* 14,07 115 37,85 68 17,21 194 150 130 65,43 122 157 -21,79 50,15 43,17 22,44 108 67 -25,06 133 128 177 55,40 0,29 103 189 170 70,92 44 56,24 214 126 62,06 80 40,59 -45,14 91 166 99 90 15,17 193 50,58 108 -21,74 30,51 94 60 64 57,83 157 188 72,31 46 67,80 224 163 71,43 56 29,46 -49,34 61 150 73 148 32,03 55,26 70 60 26,92 175 41,53 54 31 80,10 231 199 81,08 86 -15,48 187 51,74 149 52,41 -26,64 8 133 161 0,96 243 243 242 96,49 -0,24 200 200 200 81,17 -0,25 160 160 160 66,84 50,86 -0,55 122 122 121 85 -1,44 35,61 52 20,40 -1,27 a* 12,72 17,18 -1,91 -15,08 11,58 -33,22 33,37 16,15 47,55 25,11 -27,84 15,50 20,74 -41,23 52,67 -0,33 51,26 -18,46 -0,35 -0,69 -0,71 0,20 -0,36 0,47 85 52 85 52 L*a*b* (CIE D65) b* L* 13,66 38,02 16,90 65,67 -21,60 50,63 43,00 20,45 -25,17 55,68 1,54 70,99 56,13 61,14 41,12 -41,88 14,88 51,33 -22,10 31,10 56,96 71,90 64,91 71,04 30,35 -49,67 32,30 55,03 24,66 41,35 77,55 80,70 -15,28 51,14 51,15 -23,37 0,48 95,82 0,00 80,60 0,00 65,87 51,19 0,55 0,00 36,15 0,00 21,70 avg. : a* 11,80 13,67 0,37 -15,88 12,76 -30,64 28,10 17,41 42,10 24,35 -28,10 12,60 26,43 -40,14 49,30 -3,66 48,15 -19,73 -0,18 0,00 0,00 -0,20 0,00 0,00 CIELAB ΔE*ab 1,02 3,52 2,34 2,15 1,23 2,87 5,35 3,53 5,52 1,02 1,01 4,11 5,77 1,15 4,06 4,22 3,17 3,72 0,84 0,92 1,23 1,21 1,58 1,89 2,64 Table 4: Color difference between the sRGB coordinates derived from L*a*b* D50 values provided by GretagMacbeth, and the sRGB coordinates also provided by GretagMacbeth. The R’G’B’ coordinates of the “sRGB from L*a*b* D50” data set were rounded to the nearest integer before computing the color differences. The L*a*b* values are computed for D65. Because the cyan patch is close to the edge of the space gamut, we could expect to have some measurements which cross the border now and then; however, we have verified that the 20 individual R’G’B’ values of the cyan patches used for the “BabelColor Avg.” were all clipped. As an added check, for all ColorChecker patches, we compared the sRGB 1st R'G'B' data set 2nd R'G'B' data set Illum. for ΔE*ab avg. ΔE*ab sRGB from L*a*b* D50 (ColorChecker 2005) sRGB (GMB) (ColorChecker 2005) D65 2,64 1 2 3 sRGB from L*a*b* D50 (ColorChecker 2005) sRGB (BabelColor Avg.) sRGB (GMB) (ColorChecker 2005) sRGB (BabelColor Avg.) 4 Adobe RGB from L*a*b* D50 (ColorChecker 2005) Adobe RGB (BabelColor Avg.) 5 Apple RGB from L*a*b* D50 (ColorChecker 2005) Apple RGB (BabelColor Avg.) 6 ProPhoto from L*a*b* D50 (ColorChecker 2005) ProPhoto (BabelColor Avg.) D65 1,30 D65 1,95 D65 1,30 D65 1,25 D50 1,03 Table 5: Average CIELAB color differences of the 24 patches of the ColorChecker for various R’G’B’ data sets. The color difference is computed for the illuminant of the RGB space. See Table 4 for the details of how the result of the first row, “sRGB from L*a*b* D50” vs “sRGB (GMB)”, was obtained. coordinates derived from L*a*b* D50 to the values provided by GretagMacbeth (i.e. “sRGB (GMB)”). The individual color differences and their average are shown in Table 4. Many individual differences are large, with a maximum of 5,77 for the blue patch; this is quite high, even for a blue CIELAB difference. We have further compared the differences between the other R’G’B’ data sets of Table 2; the averages are shown in Table 5. For the sRGB space, the smallest average color difference (=1,30) is seen between the “sRGB from L*a*b* D50 (ColorChecker 2005)” and the “sRGB (BabelColor Avg.)” data sets. As we mentioned, the “sRGB from L*a*b* D50” data of the “ColorChecker 2005” tables was determined using the Bradford chromatic adaptation transform. In comparison, the “sRGB (GMB)” data was likely determined from the spectral reflectance data, the D65 Illuminant spectral distribution and the 2-degrees Standard Observer, a method which is generally more precise. A small numeric difference is thus expected between the two methods. However, the actual average difference between these two data sets is too high (=2,64) to be explained only by chromatic transform errors only. A rough estimate of the error introduced by the Bradford transform can be obtained by comparing the average errors of the D50 and D65 spaces in Table 5, since all D65 data derived “from L*a*b* D50” was done so using the Bradford transform. When comparing the sets of rows #2, 4 and 5 to the sets of row #6, the D65 averages are 0,22 (=1,25-1,03)

8 2006-06-01 and 0,27 (=1,30-1,03) higher than the D50 data sets (row #6). This small difference is due essentially to the Bradford transform applied to L*a*b* D50 data. From this, we infer that the sRGB values provided by GretagMacbeth came from another data set than the one used for their L*a*b* values. Overall, it can be seen that there is excellent agreement between the R’G’B’ values of the “ColorChecker 2005” data sets derived from L*a*b* values and the “BabelColor Avg.” data sets (rows #2, 4, 5, and 6). This is in fact just another way to look at what was shown in Table 1b. The best match is, as expected, between the ProPhoto data sets, since no chromatic adaptation transform was required in processing the “ColorChecker 2005” L*a*b* D50 data. It is important to note that all these differences between data sets do not indicate which set is the best. However, the better match between the “sRGB from L*a*b* D50 (ColorChecker 2005)” and the “sRGB (BabelColor Avg.)” data sets, when compared to the large difference between the two sRGB data sets of the “ColorChecker 2005” table, tend to indicate that the “sRGB (GMB)” values are less reliable. R’G’B’ values for many other common and uncommon spaces can be found in Ref. 3. 4. RGB spaces descriptions RGB spaces have evolved, sometimes for technological reasons (NTSC evolved to SMPTE-C), sometimes to fulfill professional requirements (ColorMatch, Adobe RGB), and sometimes because that’s how the display system was built and it became a, de-facto, standard (Apple RGB). A short description of the four spaces selected for Tables 2 and 3 follows. The position of their primaries on a CIE 1931 chromaticity diagram can be seen in Figure 1. Numerical specifications for each space are shown in Table 6. Adobe RGB (1998) Formerly known as SMPTE-240M for Photoshop user, this space has been renamed once the final SMPTE-240M standard committee settled for a smaller gamut6. Adobe RGB is very close to the original NTSC space and has a large enough gamut that encompasses the gamuts of most printing processes and displays. However, because of its gamut size, 16 bits per primary file formats should be preferred to 8 bits per primary ones, especially for editing purposes. While a relatively large number of those colors cannot be printed using the SWOP process (SWOP: Specifications for Web Offset Publications), particularly in the green portion of the gamut, newer printing processes, as Pantone Hexachrome, take advantage of this space. Adobe RGB’s white is defined with Illuminant D65. such Apple RGB Once a very common RGB space on the desktop, it is now slowly getting phased out and replaced by sRGB, for everyday use, and by Adobe RGB (and other larger gamut spaces) for photographic and graphic design applications. Its gamut size is similar to the ones of the ColorMatch and sRGB spaces. lookup-table (LUT) gamma which The Apple RGB, like the ColorMatch and SGI spaces, has a non-unity display is compensated by the file encoding gamma (see Section 5.4 for a discussion of gamma). In older Macintosh computers, when a value of 1,8 was entered by the user in the control panel for display gamma, filled with numbers corresponding to a gamma equal to 1,8/2,6=0,69 (or 1,45 if you define gamma using the reciprocal value =1/0,69). the LUT was ColorSync, Apple’s color management technology at the operating system level, now takes care of color management for all input and output devices and will automatically convert color data from one space to another for compliant applications. Apple RGB’s white is Illuminant D65. ProPhoto ProPhoto is a very large gamut RGB space designed by Kodak; it is getting attention from digital camera users as an archiving and working space for RAW (minimally processed, high dynamic range, and un-color-balanced) camera data. Formerly called ROMM RGB while being developed, it was renamed at the same time as its gamma was changed from 2,2 (=1/0,455) to 1,8 (=1/0,556). ProPhoto’s white is Illuminant D50. While it covers most of the visible spectrum, it also extends outside of it. As a result, about 13% of the RGB triads represent non-existent colors. Working at 16 bits per channel is a minimum with this space, and some users are concerned that even this bit depth is not enough. Others are puzzled by the decision to use a 1,8 gamma when the industry is slowly moving towards a standard 2,2 value. In any case, when used with caution for images that DO contain colors outside of the range of medium size working spaces, like Adobe RGB, it can provide improved color rendering when used in conjunction with modern wide gamut inkjet printers. sRGB With chromaticities identical to the ones defined in ITU-R BT.709-3, a High-Definition TV (HDTV) standard, sRGB, as defined in IEC 61966-2-1, strives to represent the evolution of the standard North-American TV and its convergence with the PC world. At the same time, its chromaticities are not very far from the ones of SMPTE-C (and SMPTE-240M), the present North-American TV standard, maintaining compatibility with the large quantity of recorded media. sRGB’s white is defined with Illuminant D65. Advertised as a general-purpose space for consumer use, sRGB is proposed for applications where embedding a color space profile, such as an ICC profile, may not be convenient for file size or compatibility purposes. By having all elements in a system sRGB compliant, no time is lost in conversions. The World Wide Web is obviously a target of choice for this space but it should not be discounted for other “scanner-to- printer” applications. An extended gamut color encoding standard has been defined for sRGB7; it supports multiple levels of precision while being compatible with the base standard.

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RGB Coordinates of the Macbeth ColorChecker-已解密.pdf

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