Out of Gamut: Color-Correct Vocabulary

Device-dependent: Describes a color space defined in terms of physical colorants, such as a monitor’s RGB or a printing press’ CMYK. So called because the actual color produced from a set of device-dependent values depends on the colorants and physical properties of the device in question.

Device-independent: Describes a color space defined using synthetic primaries based on human perception, independent of the properties of any physical device. Device-independent color models provide an unambiguous description of perceived color, unlike device-dependent color models.

Dye: A soluble colorant (as opposed to pigments, which are insoluble). Dyes are capable of producing brighter colors than pigments, but are less stable and less resistant to fading over time.

Dynamic Range: The range of density that a film stock, digital camera, scanner, or measuring instrument can detect, from the lowest to the highest, usually expressed in O.D. (Optical Density) units. The lowest density is termed dMin, the highest density is termed dMax.

Gamut: The range of color a device can produce, or the range of color a color model can represent.

Gamut Compression: The process where a large color gamut (for example, that of transparency film) is reduced to fit the smaller gamut of a print or display process (for example, color printing).

HSB Color Model: A color model that describes color in terms of hue, saturation, and brightness.

Hue: The property of a color that is identified by a color name, such as “red,” “green,” or “blue.” Used as a primary in the HSB (Hue, Saturation, Brightness) color model.

ICC (International Color Consortium): A group of hardware and software vendors dedicated to developing cross-platform standards for color communication and consistency.

ICC Profile: A standard format developed by the ICC for a data file that describes the color behavior of an input, display, or output device, or a color model, by referencing it to a device-independent color model such as CIE XYZ or CIELAB. Used in almost all current color-management systems.

Illuminant: A light source with known spectral power distribution.

Kelvin (K): Unit of measurement of color temperature. The Kelvin scale starts at absolute zero (-273° Celsius).

Intent: See Rendering Intent.

LCH Color Model: A derivative of CIELAB that uses cylindrical coordinates of lightness, chroma, and hue instead of the rectangular coordinate system of Lab.

Light: That small part of the electromagnetic spectrum whose wavelengths lie in the range of 380 to 720 nanometers, and hence are detectable by the human eye.

Lightness: The degree to which a color sample appears to reflect light. This attribute of color is used in the LCH (Lightness, Chroma, Hue) color model.

Magenta: One of the subtractive primary colors. Magenta absorbs all green light, reflecting red and blue.

Metamerism: The phenomenon where two color samples appear to match under one light source, and differ under another. Two such samples are called a metameric pair.

Nanometer: A unit of length equal to one-millionth of a millimeter. Visible light wavelengths are measured in nanometers.

Optical Density: The ability of a material to absorb light. The darker the material, the higher the density. Density is usually expressed on a logarithmic scale of Optical Density (O.D.) units.

Perceptual Rendering: One of the four ICC-specified rendering intents used for handling out-of-gamut colors in color matching. Perceptual rendering attempts to compress the gamut of the source space into the gamut of the destination space in such a way that the overall relationships between the colors — and hence the overall image appearance — is preserved, even though all the colors may change in the process.

Phosphors: Chemical compounds that emit light when struck by a beam of electrons. The amount of light emitted is proportional to the intensity of the electron beam. RGB monitors use three different phosphors to produce red, green, and blue light.

Photoreceptor: A mechanism that emits an electrical or chemical signal that varies in proportion to the amount of light that strikes it. CCD (charge-coupled device) sensors in desktop scanners and digital cameras, PMT (photomultiplier tubes) in drum scanners, and the rods and cones in the human retina are all photoreceptors.

Pigment: An insoluble colorant (as opposed to dyes, which are soluble). Pigments generally have better fade-resistance and permanence than dyes.

Primaries: The components of a color in a color model. They may be actual primary colors perceivable by humans, as in RGB or CMYK, or they may be imaginary mathematical constructs, as with CIE XYZ (1931) or CIELAB.

Primary Colors: The colors from which all other colors can be made. The primary colors of light are red, green, and blue. These are the additive primaries, used for transmissive or emissive color. The primary colors of pigments are cyan, magenta, and yellow, used for reflective color. It’s possible to create all colors from primary colors because the human eye contains three different types of color-sensitive photoreceptors, which are sensitive to the individual primary colors.

Profile: A data file that describes the color behavior of a physical device (such as a scanner, monitor, or printer) or that defines the color of an abstract color space (such as Adobe RGB 1998 or ColorMatch RGB) in terms of a device-independent color model (such as CIELAB or CIE XYZ). Used by color-management systems to define and match color.

Relative Colorimetric Rendering: One of the four ICC-specified rendering intents used for handling out-of-gamut colors in color matching. Relative Colorimetric rendering first scales the white of the source space to the white of the target space, adjusting all other colors relative to that white. Then it matches the adjusted colors in the source space that are inside the gamut of the target space exactly, and clips out-of-gamut colors to the nearest reproducible hue, sacrificing lightness and saturation.

Rendering Intent: A method of handling out-of-gamut colors when matching one color space to another. The ICC profile specification specifies four rendering intents: Perceptual, Absolute Colorimetric, Relative Colorimetric, and Saturation.

Saturation: The property of a color that makes it appear strongly colored. Black, white, and gray have no saturation. A red tomato has high saturation. Pastel colors have low saturation. Also known as Chroma. (This attribute of color is used in the HLS (Hue, Lightness, Saturation) and HSB (Hue, Saturation, Brightness) color models.

Saturation Rendering: One of the four ICC-specified rendering intents used for handling out-of-gamut colors in color matching. Saturation rendering maps fully-saturated colors in the source space to fully saturated colors in the target space, sacrificing hue and lightness.


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Bruce Angus Fraser (9 January 1954 – 16 December 2006) was an author who specialized in digital color technology, including hardware and software for creating and managing color images and publications. He co-authored "Real World Photoshop" and others. He was a founding member of PixelGenius, LLC.
  • anonymous says:

    I guess that’s what “gurus” are for.

    John Holmes

  • anonymous says:

    Thank you for this reference. I will keep this within arm’s reach. It is great to have. John McClure

  • anonymous says:

    Mr. Fraser, I knew you always had it in you .

  • Anonymous says:

    there was no green and no red why were they not there?!!

  • Anonymous says:

    In point of fact, pastels have very high chroma. The reason is they are pure pigments, and unadulterated by additives. Your point in chroma must be based on the popular use of pastel as a descriptor of 17th century portrait colors. Get with the times!

  • Liz Walton says:

    thanks so much for the reference. Excellent.

  • Liz Walton says:

    thanks so much for the reference. Excellent.

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