ColorChecker

ColorChecker held in a photographic portrait setting
Nominal chromaticities of ColorChecker patches in the CIE 1931 xy chromaticity diagram (in the SVG version, hover over a color swatch to highlight it; click it to select and deselect it)

The ColorChecker Color Rendition Chart (often referred to by its original name, the Macbeth ColorChecker[1] or simply Macbeth chart[2]) 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.[3] 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 by 8.25 inches (27.9 by 21.0 cm), or in its original incarnation about 13 by 9 inches (33 by 23 cm), an aspect ratio approximately the same as that of 35 mm film.[4] It includes 24 patches in a 4 × 6 grid, each slightly under 2 inches (5.1 cm) 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.[3]

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 reflectance spectra, it is possible to derive CIELAB coordinates for Illuminants D65 and D50 and coordinates in sRGB.[5]

Table from Field (1990); CIE data for Illuminant C from Poynton (2008).[4][6]
Index Description Munsell Notation CIE xyY' Manufacturer's sRGB D65 color values[7]
Row 1: Natural colors
1 Dark skin 3 YR 3.7/3.2 0.400 0.350 10.1 #735244
2 Light skin 2.2 YR 6.47/4.1 0.377 0.345 35.8 #c29682
3 Blue sky 4.3 PB 4.95/5.5 0.247 0.251 19.3 #627a9d
4 Foliage 6.7 GY 4.2/4.1 0.337 0.422 13.3 #576c43
5 Blue flower 9.7 PB 5.47/6.7 0.265 0.240 24.3 #8580b1
6 Bluish green 2.5 BG 7/6 0.261 0.343 43.1 #67bdaa
Row 2: Miscellaneous colors
7 Orange 5 YR 6/11 0.506 0.407 30.1 #d67e2c
8 Purplish blue 7.5 PB 4/10.7 0.211 0.175 12.0 #505ba6
9 Moderate red 2.5 R 5/10 0.453 0.306 19.8 #c15a63
10 Purple 5 P 3/7 0.285 0.202 6.6 #5e3c6c
11 Yellow green 5 GY 7.1/9.1 0.380 0.489 44.3 #9dbc40
12 Orange yellow 10 YR 7/10.5 0.473 0.438 43.1 #e0a32e
Row 3: Primary and secondary colors
13 Blue 7.5 PB 2.9/12.7 0.187 0.129 6.1 #383d96
14 Green 0.25 G 5.4/9.6 0.305 0.478 23.4 #469449
15 Red 5 R 4/12 0.539 0.313 12.0 #af363c
16 Yellow 5 Y 8/11.1 0.448 0.470 59.1 #e7c71f
17 Magenta 2.5 RP 5/12 0.364 0.233 19.8 #bb5695
18 Cyan 5 B 5/8 0.196 0.252 19.8 #0885a1
Row 4: Grayscale colors
19 White N 9.5/ 0.310 0.316 90.0 #f3f3f2
20 Neutral 8 N 8/ 0.310 0.316 59.1 #c8c8c8
21 Neutral 6.5 N 6.5/ 0.310 0.316 36.2 #a0a0a0
22 Neutral 5 N 5/ 0.310 0.316 19.8 #7a7a79
23 Neutral 3.5 N 3.5/ 0.310 0.316 9.0 #555555
24 Black N 2/ 0.310 0.316 3.1 #343434

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.[8]

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.

See also

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. ↑ "Computational Color Imaging - Alain Trémeau - Google Books". Retrieved 12 October 2015.
  3. 1 2 C. S. McCamy, H. Marcus, and J. G. Davidson (1976). "A Color-Rendition Chart". Journal of Applied Photographic Engineering 2(3). 95–99.
  4. 1 2 Charles Poynton (2008). "ColorChecker (‘Macbeth’) Chart". poynton.com
  5. ↑ 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.
  6. ↑ Field, Gary G. (1990), Color Scanning and Imaging Systems, Pittsburg, PA: Graphic Arts Technical Foundation, ISBN 0-88362-120-7
  7. ↑ ColorChecker Colorimetric Data (PDF), archived from the original (PDF) on 2012-04-18, retrieved 2012-04-17
  8. ↑ For example, Roy S. Berns and Lawrence A. Taplin (2006). "Practical Spectral Imaging Using a Color-Filter Array Digital Camera".
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