ColorChecker
Encyclopedia
Color chart
In color-related fields, a color chart is a flat, physical object colored with an arrangement of standardized color samples, used for color comparisons and measurements such as checking the color reproduction of an imaging system...
(often referred to by its original name, the Macbeth ColorChecker) is a color calibration
Color calibration
The aim of color calibration is to measure and/or adjust the color response of a device to a known state. In ICC terms this is the basis for a additional color characterization of the device and later profiling. In non ICC workflows calibration refers sometimes to establishing a known relationship...
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. 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
Color constancy
Color constancy is an example of subjective constancy and a feature of the human color perception system which ensures that the perceived color of objects remains relatively constant under varying illumination conditions. A green apple for instance looks green to us at midday, when the main...
under a variety of lighting conditions, especially as detected by typical color photographic film
Photographic film
Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and resolution of the film...
, and to be stable over time.
Design
The ColorChecker chart is a rectangular card measuring about , or in its original incarnation about , an aspect ratio approximately the same as that of 35 mm film35 mm film
35 mm film is the film gauge most commonly used for chemical still photography and motion pictures. The name of the gauge refers to the width of the photographic film, which consists of strips 35 millimeters in width...
. It includes 24 patches in a 4 × 6 grid, each slightly under square, made of matte
Gloss (material appearance)
Gloss is an optical property, which is based on the interaction of light with physical characteristics of a surface. It is actually the ability of a surface to reflect light into the specular direction. The factors that affect gloss are the refractive index of the material, the angle of incident...
paint applied to smooth paper, and surrounded by a black border. Six of the patches form a uniform gray lightness
Lightness (color)
Lightness is a property of a color, or a dimension of a color space, that is defined in a way to reflect the subjective brightness perception of a color for humans along a lightness–darkness axis. A color's lightness also corresponds to its amplitude.Various color models have an explicit term for...
scale, and another six are primary colors
Primary Colors
Primary Colors: A Novel of Politics is a roman à clef, a work of fiction that purports to describe real life characters and events — namely, Bill Clinton's first presidential campaign in 1992...
typical of chemical photographic processes – red
Red
Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 630–740 nm. Longer wavelengths than this are called infrared , and cannot be seen by the naked eye...
, green
Green
Green is a color, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 520–570 nanometres. In the subtractive color system, it is not a primary color, but is created out of a mixture of yellow and blue, or yellow and cyan; it is considered...
, blue
Blue
Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440–490 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal...
, cyan
Cyan
Cyan from , transliterated: kýanos, meaning "dark blue substance") may be used as the name of any of a number of colors in the blue/green range of the spectrum. In reference to the visible spectrum cyan is used to refer to the color obtained by mixing equal amounts of green and blue light or the...
, magenta
Magenta
Magenta is a color evoked by light stronger in blue and red wavelengths than in yellowish-green wavelengths . In light experiments, magenta can be produced by removing the lime-green wavelengths from white light...
, and yellow
Yellow
Yellow is the color evoked by light that stimulates both the L and M cone cells of the retina about equally, with no significant stimulation of the S cone cells. Light with a wavelength of 570–590 nm is yellow, as is light with a suitable mixture of red and green...
. The remaining colors include approximations of medium light and medium dark human skin
Human skin color
Human skin color is primarily due to the presence of melanin in the skin. Skin color ranges from almost black to white with a pinkish tinge due to blood vessels underneath. Variation in natural skin color is mainly due to genetics, although the evolutionary causes are not completely certain...
, blue sky
Sky
The sky is the part of the atmosphere or outer space visible from the surface of any astronomical object. It is difficult to define precisely for several reasons. During daylight, the sky of Earth has the appearance of a pale blue surface because the air scatters the sunlight. The sky is sometimes...
, the front of a typical leaf
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
, and a blue chicory
Chicory
Common chicory, Cichorium intybus, is a somewhat woody, perennial herbaceous plant usually with bright blue flowers, rarely white or pink. Various varieties are cultivated for salad leaves, chicons , or for roots , which are baked, ground, and used as a coffee substitute and additive. It is also...
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
Orange (fruit)
An orange—specifically, the sweet orange—is the citrus Citrus × sinensis and its fruit. It is the most commonly grown tree fruit in the world....
and lemon
Lemon
The lemon is both a small evergreen tree native to Asia, and the tree's ellipsoidal yellow fruit. The fruit is used for culinary and non-culinary purposes throughout the world – primarily for its juice, though the pulp and rind are also used, mainly in cooking and baking...
s.
Colors
The colors of the chart were described by McCamy et al. with colorimetricColorimetry
Colorimetry is "the science and technology used to quantify and describe physically the human color perception."It is similar to spectrophotometry, but is distinguished by its interest in reducing spectra to the physical correlates of color perception, most often the CIE 1931 XYZ color space...
measurements using the CIE 1931 2° standard observer
CIE 1931 color space
In the study of color perception, one of the first mathematically defined color spaces is the CIE 1931 XYZ color space, created by the International Commission on Illumination in 1931....
and Illuminant
Standard illuminant
A standard illuminant is a theoretical source of visible light with a profile which is published. Standard illuminants provide a basis for comparing images or colors recorded under different lighting.-CIE illuminants:...
C, and also in terms of the Munsell color system
Munsell color system
In colorimetry, the Munsell color system is a color space that specifies colors based on three color dimensions: hue, value , and chroma . It was created by Professor Albert H...
. Using measured spectral reflectance curves, it is possible to derive CIELAB values for Illuminants D65 and D50 and coordinates in sRGB.
- Table from Field (1990); CIE data for Illuminant C from Poynton (2008).
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 spectrophotometricSpectrophotometry
In chemistry, spectrophotometry is the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength...
measurements are available, the ColorChecker has also been used in academic research into topics such as spectral imaging
Spectral imaging
Spectral imaging is a branch of spectroscopy and of photography in which a complete spectrum or some spectral information is collected at every location in an image plane...
.
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.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 illuminantStandard illuminantA standard illuminant is a theoretical source of visible light with a profile which is published. Standard illuminants provide a basis for comparing images or colors recorded under different lighting.-CIE illuminants:...
s 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.