ColorChecker

A ColorChecker being held in a photographic portrait setting

The ColorChecker Color Rendition Chart (often referred to by its original name, the Macbeth ColorChecker^[1]) is a color calibration target consisting of a cardboard-framed arrangement of 24 squares of painted samples. The ColorChecker was introduced in a 1976 paper by McCamy, Marcus, and Davidson in the Journal of Applied Photographic Engineering.^[2] The chart’s color patches have spectral reflectances intended to mimic those of natural objects such as human skin, foliage, and flowers, to have consistent color appearance under a variety of lighting conditions, especially as detected by typical color photographic film, and to be stable over time.

Design

The ColorChecker chart is a rectangular card measuring about 11 × 8.25 inches, or in its original incarnation about 13 × 9 in., an aspect ratio approximately the same as that of 35 mm film.^[3] It includes 24 patches in a 4 × 6 grid, each slightly under 2 inches square, made of matte paint applied to smooth paper, and surrounded by a black border. Six of the patches form a uniform gray lightness scale, and another six are primary colors typical of chemical photographic processes – red, green, blue, cyan, magenta, and yellow. The remaining colors include approximations of medium light and medium dark human skin, blue sky, the front of a typical leaf, and a blue chicory flower. The rest were chosen arbitrarily to represent a gamut "of general interest and utility for test purposes", though the orange and yellow patches are similarly colored to typical oranges and lemons.^[2]

Colors

The colors of the chart were described by McCamy et al. with colorimetric measurements using the CIE 1931 2° standard observer and Illuminant C, and also in terms of the Munsell color system. Using measured spectral reflectance curves, it is possible to derive CIELAB values for Illuminants D₆₅ and D₅₀ and coordinates in sRGB.^[4]

Table from Field (1990); CIE data for Illuminant C from Poynton (2008).^[3][5]

Index	Description	Munsell Notation	CIE xyY	Approximate RGB color
Row 1: Natural colors
1	Dark skin	3 YR 3.7/3.2	0.400 0.350 10.1	#6f4f38
2	Light skin	2.2 YR 6.47/4.1	0.377 0.345 35.8	#ceaa99
3	Blue sky	4.3 PB 4.95/5.5	0.247 0.251 19.3	#5e8fb8
4	Foliage	6.7 GY 4.2/4.1	0.337 0.422 13.3	#607c43
5	Blue flower	9.7 PB 5.47/6.7	0.265 0.240 24.3	#9b97d2
6	Bluish green	2.5 BG 7/6	0.261 0.343 43.1	#8ddad6
Row 2: Miscellaneous colors
7	Orange	5 YR 6/11	0.506 0.407 30.1	#d98404
8	Purplish blue	7.5 PB 4/10.7	0.211 0.175 12.0	#3764b9
9	Moderate red	2.5 R 5/10	0.453 0.306 19.8	#d55f72
10	Purple	5 P 3/7	0.285 0.202 6.6	#6d2181
11	Yellow green	5 GY 7.1/9.1	0.380 0.489 44.3	#bcd448
12	Orange Yellow	10 YR 7/10.5	0.473 0.438 43.1	#f0bb30
Row 3: Primary colors
13	Blue	7.5 PB 2.9/12.7	0.187 0.129 6.1	#004291
14	Green	0.1 G 5.4/9.6	0.305 0.478 23.4	#45a53f
15	Red	5 R 4/12	0.539 0.313 12.0	#d11b3f
16	Yellow	5 Y 8/11.1	0.448 0.470 59.1	#ecd621
17	Magenta	2.5 RP 5/12	0.364 0.233 19.8	#dc41b7
18	Cyan	5 B 5/8	0.196 0.252 19.8	#00acc1
Row 4: Grayscale colors
19	White	N 9.5/	0.310 0.316 90.0	#e8e8e8
20	Neutral 8	N 8/	0.310 0.316 59.1	#d0ced9
21	Neutral 6.5	N 6.5/	0.310 0.316 36.2	#abb0b4
22	Neutral 5	N 5/	0.310 0.316 19.8	#7e8a8a
23	Neutral 3.5	N 3.5/	0.310 0.316 9.0	#4e5c5c
24	Black	N 2/	0.310 0.316 3.1	#273333

Use

Color targets such as the ColorChecker can be captured by cameras and other color input devices, and the resulting images’ output can be compared to the original chart, or to reference measurements, to test the degree to which image acquisition reproduction systems and processes approximate the human visual system’s. Because of its wide availability and use, its careful design, and its consistency, and because comprehensive spectrophotometric measurements are available, the ColorChecker has also been used in academic research into topics such as spectral imaging.^[6]

ColorChecker Digital SG

X-Rite also sells a 140-patch chart called the ColorChecker Digital SG, and is intended for automated use with computer software to characterize digital cameras and scanners.

References

1. ^ The ColorChecker was originally produced by Macbeth (then a subsidiary of Kollmorgen), which through a series of mergers and acquisitions now belongs to X-Rite.
2. ^ ^{a b} C. S. McCamy, H. Marcus, and J. G. Davidson (1976). "A Color-Rendition Chart". Journal of Applied Photographic Engineering 2(3). 95–99.
3. ^ ^{a b} Charles Poynton (2008). "ColorChecker (‘Macbeth’) Chart". poynton.com
4. ^ Measured reflectance spectra are available from the Munsell Color Science Laboratory website in html and Excel formats, taken from measurements published in Noboru Ohta (1997). "The Basis of Color Reproduction Engineering" (Japanese). Corona-sha Company of Japan.
   See also Danny Pascale’s page.
5. ^ Field, Gary G. (1990), Color Scanning and Imaging Systems, Pittsburg, PA: Graphic Arts Technical Foundation, ISBN 0-88362-120-7 
6. ^ For example, Roy S. Berns and Lawrence A. Taplin (2006). "Practical Spectral Imaging Using a Color-Filter Array Digital Camera".

External links

• "ColorChecker Classic" official product page at the X-Rite website.
  • "ColorChecker Digital SG" product page
• Danny Pascale (2009). "The ColorChecker (since 1976!)". Babelcolor.com. This extensive page includes a history of the chart, average spectrophotometric measurements from 20 ColorCheckers (the precise tools used for these measurements is unclear), calculated RGB values in a variety of RGB color spaces, a list of places to buy charts, and advice for using the data in practical camera calibration and image applications.
  • Danny Pascale (2006) "RGB coordinates of the Macbeth ColorChecker". Includes comparisons in CIELAB and RGB values based on spectrophotometric measurements vs. provided by Gretag–Macbeth
• Bruce Lindbloom (2007). "How the ColorChecker Calculator Works". brucelindbloom.com. Lindbloom measured the spectral reflectances his own copy of the ColorChecker, and created a Java applet to calculate colorimetric coordinates under various standard illuminants and in various RGB color spaces
  • Bruce Lindbloom (2008). "ColorChecker RGB Summaries, Spreadsheets and Lab TIFF File". brucelindbloom.com. A page showing RGB values for color patches in various RGB color spaces, based on the applet described above, and a set of Excel spreadsheets for comparing these numbers to those in a digital camera or scanner image of the ColorChecker.