ColorChecker

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ColorChecker held in a photographic portrait setting Gretag-Macbeth ColorChecker.jpg
ColorChecker held in a photographic portrait setting
ColorChecker Passport ColorChecker Passport.png
ColorChecker Passport
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) CIE1931xy ColorChecker SMIL.svg
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.

Contents

In 2006, Gretag-Macbeth was acquired by X-Rite. In 2021, X-Rite spun off its consumer-level calibration products to a separate company Calibrite, which is currently producing the ColorChecker under the Calibrite brand name. [4]

Design

The ColorChecker Classic 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. [5] 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]

There is also a ColorCheckerPassport, a smaller version of the ColorChecker Classic with the same 24 chips but in a tri-fold version with some additional patches on two of the pages. Its dimensions are 125 mm (H) × 90 mm (W) × 9 mm (T). The pigments for ColorCheckerPassport were modified in November 2014, so the current available cards do not have exactly the same carnation, and hence RGB numbers, as before, and particularly are not the ones provided on next section.

Colors

PDF version of the chart Color Checker.pdf
PDF version of the chart

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 (D65). [6]

Table from Field (1990); CIE data for Illuminant C from Poynton (2008). [5] [7]
IndexDescriptionMunsell NotationCIE xyYManufacturer's sRGB color values [8] Reflectance Rel. MgCO3
Row 1: Natural colors
1Dark skin3 YR 3.7/3.20.400 0.350 10.1#735244
2Light skin2.2 YR 6.47/4.10.377 0.345 35.8#c29682
3Blue sky4.3 PB 4.95/5.50.247 0.251 19.3#627a9d
4Foliage6.7 GY 4.2/4.10.337 0.422 13.3#576c43
5Blue flower9.7 PB 5.47/6.70.265 0.240 24.3#8580b1
6Bluish green2.5 BG 7/60.261 0.343 43.1#67bdaa
Row 2: Miscellaneous colors
7Orange5 YR 6/110.506 0.407 30.1#d67e2c
8Purplish blue7.5 PB 4/10.70.211 0.175 12.0#505ba6
9Moderate red2.5 R 5/100.453 0.306 19.8#c15a63
10Purple5 P 3/70.285 0.202 6.6#5e3c6c
11Yellow green5 GY 7.1/9.10.380 0.489 44.3#9dbc40
12Orange yellow10 YR 7/10.50.473 0.438 43.1#e0a32e
Row 3: Primary and secondary colors
13Blue7.5 PB 2.9/12.70.187 0.129 6.1#383d96
14Green0.25 G 5.4/9.60.305 0.478 23.4#469449
15Red5 R 4/120.539 0.313 12.0#af363c
16Yellow5 Y 8/11.10.448 0.470 59.1#e7c71f
17Magenta2.5 RP 5/120.364 0.233 19.8#bb5695
18Cyan5 B 5/80.196 0.252 19.8#0885a1
Row 4: Grayscale colors
19WhiteN 9.5/0.310 0.316 90.0#f3f3f390.0%
20Neutral 8N 8/0.310 0.316 59.1#c8c8c859.7%
21Neutral 6.5N 6.5/0.310 0.316 36.2#a0a0a036.1%
22Neutral 5N 5/0.310 0.316 19.8#7a7a7a18.4%
23Neutral 3.5N 3.5/0.310 0.316 9.0#55555518.6%
24BlackN 2/0.310 0.316 3.1#3434343.0%

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 systems. It can also be used to color correct one photo with the chart in it (that may have a different color cast, for example due to a lighting coloration difference) to another "reference" photo with the chart in it.

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. [9]

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

Related Research Articles

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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. ↑ Trémeau, Alain; Schettini, Raimondo; Tominaga, Shoji (29 July 2009). Computational Color Imaging – Alain Trémeau – Google Books. Springer. ISBN   978-3-642-03265-3 . 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 Engineering2(3). 95–99.
  4. ↑ "Some X-Rite Products Rebranding to Calibrite". Image Science.
  5. 1 2 Charles Poynton (2008). "ColorChecker (‘Macbeth’) Chart". poynton.com
  6. ↑ Measured reflectance spectra are available Archived 10 November 2012 at the Wayback Machine from the Munsell Color Science Laboratory website in html Archived 4 March 2016 at the Wayback Machine and Excel Archived 21 November 2014 at the Wayback Machine 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.
  7. ↑ Field, Gary G. (1990), Color Scanning and Imaging Systems, Pittsburgh, PA: Graphic Arts Technical Foundation, ISBN   0-88362-120-7
  8. ↑ ColorChecker Colorimetric Data (PDF), archived (PDF) from the original on 9 October 2012, retrieved 17 April 2012
  9. ↑ For example, Roy S. Berns and Lawrence A. Taplin (2006). "Practical Spectral Imaging Using a Color-Filter Array Digital Camera".
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