Absolute color space
Encyclopedia
In color science, there are two meanings of the term absolute color space:
In this article, we concentrate on the second definition.
CIEXYZ
and sRGB are examples of absolute color spaces, as opposed to a generic RGB color space
.
A non-absolute color space can be made absolute by defining its relationship to absolute colorimetric quantities. For instance, if the red, green, and blue colors in a monitor are measured exactly, together with other properties of the monitor, then RGB values on that monitor can be considered as absolute. The L*a*b*
is sometimes referred to as absolute, though it also needs a white point
specification to make it so.
A popular way to make a color space like RGB into an absolute color is to define an ICC
profile, which contains the attributes of the RGB. This is not the only way to express an absolute color, but it is the standard in many industries. RGB colors defined by widely accepted profiles include sRGB
and Adobe RGB
. The process of adding an ICC profile
to a graphic or document is sometimes called tagging or embedding; tagging therefore marks the absolute meaning of colors in that graphic or document.
limitations, and converting colors that lie outside that gamut will not produce correct results. There are also likely to be rounding errors, especially if the popular range of only 256 distinct values per component (8-bit color
) is used.
One part of the definition of an absolute color space is the viewing conditions. The same color, viewed under different natural or artificial lighting conditions, will look different. Those involved professionally with color matching may use viewing rooms, lit by standardized lighting.
Occasionally, there are precise rules for converting between non-absolute color spaces. For example HSL and HSV spaces are defined as mappings of RGB. Both are non-absolute, but the conversion between them should maintain the same color. However, in general, converting between two non-absolute color spaces (for example, RGB to CMYK
) or between absolute and non-absolute color spaces (for example, RGB to L*a*b*) is almost a meaningless concept.
, a proprietary system that includes swatch cards and recipes that commercial printers can use to make inks that are a particular color.
- A color spaceColor spaceA color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components...
in which the perceptual difference between colors is directly related to distances between colorsColor differenceThe difference or distance between two colors is a metric of interest in color science. It allows people to quantify a notion that would otherwise be described with adjectives, to the detriment of anyone whose work is color critical...
as represented by points in the color space. - A color spaceColor spaceA color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components...
in which colors are unambiguous, that is, where the interpretations of colors in the space are colorimetrically defined without reference to external factors.
In this article, we concentrate on the second definition.
CIEXYZ
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 sRGB are examples of absolute color spaces, as opposed to a generic RGB color space
RGB color space
An RGB color space is any additive color space based on the RGB color model. A particular RGB color space is defined by the three chromaticities of the red, green, and blue additive primaries, and can produce any chromaticity that is the triangle defined by those primary colors...
.
A non-absolute color space can be made absolute by defining its relationship to absolute colorimetric quantities. For instance, if the red, green, and blue colors in a monitor are measured exactly, together with other properties of the monitor, then RGB values on that monitor can be considered as absolute. The L*a*b*
Lab color space
A Lab color space is a color-opponent space with dimension L for lightness and a and b for the color-opponent dimensions, based on nonlinearly compressed CIE XYZ color space coordinates....
is sometimes referred to as absolute, though it also needs a white point
White point
A white point is a set of tristimulus values or chromaticity coordinates that serve to define the color "white" in image capture, encoding, or reproduction. Depending on the application, different definitions of white are needed to give acceptable results...
specification to make it so.
A popular way to make a color space like RGB into an absolute color is to define an ICC
International Color Consortium
The International Color Consortium was formed in 1993 by eight industry vendors in order to create a universal color management system that would function transparently across all operating systems and software packages....
profile, which contains the attributes of the RGB. This is not the only way to express an absolute color, but it is the standard in many industries. RGB colors defined by widely accepted profiles include sRGB
SRGB color space
sRGB is a standard RGB color space created cooperatively by HP and Microsoft in 1996 for use on monitors, printers, and the Internet.sRGB uses the ITU-R BT.709 primaries, the same as are used in studio monitors and HDTV, and a transfer function typical of CRTs...
and Adobe RGB
Adobe RGB color space
The Adobe RGB color space is an RGB color space developed by Adobe Systems in 1998. It was designed to encompass most of the colors achievable on CMYK color printers, but by using RGB primary colors on a device such as the computer display...
. The process of adding an ICC profile
ICC profile
In color management, an ICC profile is a set of data that characterizes a color input or output device, or a color space, according to standards promulgated by the International Color Consortium...
to a graphic or document is sometimes called tagging or embedding; tagging therefore marks the absolute meaning of colors in that graphic or document.
Conversion
A color in one absolute color space can be converted into another absolute color space, and back again, in general; however, some color spaces may have gamutGamut
In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain complete subset of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circumstance, such as within a given color space or by a...
limitations, and converting colors that lie outside that gamut will not produce correct results. There are also likely to be rounding errors, especially if the popular range of only 256 distinct values per component (8-bit color
8-bit color
8-bit color graphics is a method of storing image information in a computer's memory or in an image file, such that each pixel is represented by one 8-bit byte. The maximum number of colors that can be displayed at any one time is 256....
) is used.
One part of the definition of an absolute color space is the viewing conditions. The same color, viewed under different natural or artificial lighting conditions, will look different. Those involved professionally with color matching may use viewing rooms, lit by standardized lighting.
Occasionally, there are precise rules for converting between non-absolute color spaces. For example HSL and HSV spaces are defined as mappings of RGB. Both are non-absolute, but the conversion between them should maintain the same color. However, in general, converting between two non-absolute color spaces (for example, RGB to CMYK
CMYK color model
The CMYK color model is a subtractive color model, used in color printing, and is also used to describe the printing process itself. CMYK refers to the four inks used in some color printing: cyan, magenta, yellow, and key...
) or between absolute and non-absolute color spaces (for example, RGB to L*a*b*) is almost a meaningless concept.
Other absolute color spaces
A different method of defining absolute color spaces is familiar to many consumers as the swatch card, used to select paint, fabrics, and the like. This is a way of agreeing a color between two parties. A more standardized method of defining absolute colors is the Pantone Matching SystemPantone
Pantone Inc. is a corporation headquartered in Carlstadt, New Jersey, USA. The company is best known for its Pantone Matching System , a proprietary color space...
, a proprietary system that includes swatch cards and recipes that commercial printers can use to make inks that are a particular color.