iPedia Free Information Center

Information about Color Gamut

This article is about color gamut. For other uses, see Gamut (disambiguation).


In color reproduction, including computer graphics and photography, the gamut, or color gamut (pronounced /ˈgæmət/), 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 certain output device. Another sense, less frequently used but not less correct, refers to the complete set of colors found within an image at a given time. In this context, digitizing a photograph, converting a digitized image to a different color space, or outputting it to a given medium using a certain output device generally alters its gamut, in the sense that some of the colors in the original are lost in the process.

Introduction

The term gamut was adopted from the music field, where it meant the set of pitches of which musical melodies were composed; Shakespeare's use of the term in The Taming of the Shrew is sometimes attributed to another author/musician, Thomas Morley[1]. In the 1850s, the term was being applied to a range of colors or hue, for example by Thomas De Quincey who wrote, "Porphyry, I have heard, runs through as large a gamut of hues as marble."[2]

In color theory, the gamut of a device or process is that portion of the color space that can be represented, or reproduced. Generally, the color gamut is specified in the hue–saturation plane, as many systems can produce colors with a wide range intensity within their color gamut; in addition, for subtractive color systems, such as printing, the range of intensity available in the system is for the most part meaningless outside the context of its illumination.

When certain colors cannot be displayed within a particular color model, those colors are said to be out of gamut. For example, pure red which is contained in the RGB color model gamut is out of gamut in the CMYK model.

A device that is able to reproduce the entire visible color space is somewhat of a holy grail in the engineering of color displays and printing processes. While modern techniques allow increasingly good approximations, the complexity of these systems often makes them impractical. What is "good enough" is dictated by the limitations of human perception.

While processing a digital image, the most convenient color model used is the RGB model. Printing the image requires transforming the image from the original RGB color space to the printer's CMYK color space. During this process, the colors from the RGB which are out of gamut must be somehow converted to approximate values within the CMYK space gamut. Simply trimming only the colors which are out of gamut to the closest colors in the destination space would burn the image. There are several algorithms approximating this transformation, but none of them can be truly perfect, since those colors are simply out of the target device's capabilities. This is why identifying the colors in an image which are out of gamut in the target color space as soon as possible during processing is critical for the quality of the final product.

Representation of gamuts



Gamuts are commonly represented as areas in the CIE 1931 chromaticity diagram as shown at right, with the curved edge representing the monochromatic colors. Gamut areas typically have triangular shapes because most color reproduction is done with three primaries.

However, the accessible gamut depends on the brightness; a full gamut must therefore be represented in 3D space, as below:
The pictures at left show the gamuts of RGB color space (top), such as on computer monitors, and of reflective colors in nature (bottom). The cone drawn in grey corresponds roughly to the CIE diagram at right, with the added dimension of brightness.

The axes in these diagrams are the responses of the short-wavelength, middle-wavelength, and long-wavelength cones in the human eye. The other letters indicate black, red, green, blue, cyan, magenta, yellow, and white colors. (Note: These pictures are not exactly to scale.)

The left diagram shows that the shape of the RGB gamut is a triangle between red, green, and blue at lower luminosities; a triangle between cyan, magenta, and yellow at higher luminosities, and a single white point at maximum luminosity. The exact positions of the apexes depends on the emission spectra of the phosphors in the computer monitor, and on the ratio between the maximum luminosities of the three phosphors (i.e., the color balance).

The gamut of the CMYK color space is, ideally, approximately the same as that for RGB, with slightly different apexes, depending on both the exact properties of the dyes and the light source. In practice, due to the way raster-printed colors interact with each other and the paper and due to their non-ideal absorption spectra, the gamut is smaller and has rounded corners.

The gamut of reflective colors in nature has a similar, though more rounded, shape. An object that reflects only a narrow band of wavelengths will have a color close to the edge of the CIE diagram, but it will have a very low luminosity at the same time. At higher luminosities, the accessible area in the CIE diagram becomes smaller and smaller, up to a single point of white, where all wavelengths are reflected exactly 100 per cent. The exact coordinates of white are of course determined by the color of the light source.

Limitations of color representation

The color gamut of most systems can be understood as a result of difficulties producing pure monochromatic (single wavelength) light. The best technological source of (nearly) monochromatic light is the laser, which is expensive and impractical for many systems (as laser technology improves and becomes more inexpensive, this may no longer be the case). Other than lasers, most systems represent highly saturated colors with a more or less crude approximation, which includes light with a range of wavelengths besides the desired color. This may be more pronounced for some hues than others.

Systems which use additive color processes usually have a color gamut which is roughly a convex polygon in the hue-saturation plane. The vertices of the polygon are the most saturated colors the system can produce. In subtractive color systems, the color gamut is more often an irregular region.

Comparison of various systems

Following is a list of representative color systems more or less ordered from large to small color gamut:
  • Laser video projector uses 3 lasers to produce the broadest gamut available in practical display equipment today, derived from the fact that lasers produce truly monochromatic primaries. The systems work either by scanning the entire picture a dot at a time and modulating the laser directly at high frequency, much like the electron beams in a CRT, or by optically spreading and then modulating the laser and scanning a line at a time, the line itself being modulated in much the same way as in a DLP.
  • Photographic film can reproduce a larger color gamut than typical television, computer, or home video systems.[3]
  • Laser light shows use lasers to produce very nearly monochromatic light, allowing colors far more saturated than those produced by other systems. However, mixing hues to produce less saturated colors is difficult. In addition, such systems are complex, expensive, and ill-suited to general video display.
  • CRT and similar video displays have a roughly triangular color gamut which covers a significant portion of the visible color space. In CRTs, the limitations are due to the phosphors in the screen which produce red, green, and blue light.
  • Liquid crystal display (LCD) screens filter the light emitted by a backlight. The gamut of an LCD screen is therefore limited to the emitted spectrum of the backlight. Typical LCD screens use fluorescent bulbs for backlights. LCD Screens with certain LED backlights yield a more comprehensive gamut than CRTs.
  • Television uses a CRT display (usually), but does not take full advantage of its color display properties, due to the limitations of broadcasting. HDTV is far better, but still somewhat less than, for example, computer displays using the same display technology.
  • Paint mixing, both artistic and for commercial applications, achieves a reasonably large color gamut by starting with a larger palette than the red, green, and blue of CRTs or cyan, magenta, and yellow of printing. Paint may reproduce some highly saturated colors that can not be reproduced well by CRTs (particularly violet), but overall the color gamut is smaller.
  • Printing typically uses the CMYK color space (cyan, magenta, yellow, and black). A very few printing processes do not include black; however, those processes (with the exception of dye-sublimation printers) are poor at representing low saturation, low intensity colors. Efforts have been made to expand the gamut of the printing process by adding inks of non-primary colors; these are typically orange and green (see Hexachrome) or light cyan and light magenta. Spot color inks of a very specific color are also sometimes used.
  • A monochrome display's color gamut is a one-dimensional curve in color space.

References

1. ^ John H. Long (Jan. 1950). Shakespeare and Thomas Morley.
2. ^ Thomas De Quincey (1854). De Quincey's works. James R. Osgood. 
3. ^ Film gamut, apples, and oranges. Retrieved on 26 April 2007.

External links

gamut originally referred to lowest note (the “gamma-ut”) in the musical scale used in medieval music, and then to the entirety of the medieval musical scale. From this notion of a complete range, the term came to be applied to other fields, including as a completely
..... Click the link for more information.
Computer graphics is a sub-field of computer science and is concerned with digitally synthesizing and manipulating visual content. Although the term often refers to three-dimensional computer graphics, it also encompasses two-dimensional graphics and image processing.
..... Click the link for more information.
Photography [fә'tɑgrәfi:],[foʊ'tɑgrәfi:] is the process of recording pictures by means of capturing light on a light-sensitive medium, such as a film or electronic sensor.
..... Click the link for more information.
Color or colour[1] (see spelling differences) is the visual perceptual property corresponding in humans to the categories called red, yellow, blue, black, etc.
..... Click the link for more information.
color space. For example, Adobe RGB and sRGB are two different absolute color spaces, both based on the RGB model.

In the most generic sense of the definition above, color spaces can be defined without the use of a color model.
..... Click the link for more information.
An output device is any piece of computer hardware equipment used to communicate the results of data processing carried out by an information processing system (such as a computer) to the outside world.
..... Click the link for more information.
William Shakespeare

The Chandos portrait, artist and authenticity unconfirmed. National Portrait Gallery, London.
Born: April 1564 (exact date unknown)
Stratford-upon-Avon, Warwickshire, England
Died: 23 March 1616
Stratford-upon-Avon, Warwickshire, England
..... Click the link for more information.
Thomas Morley (1557 or 1558 – October 1602) was an English composer, theorist, editor and organist of the Renaissance, and the foremost member of the English Madrigal School.
..... Click the link for more information.
Color Theory is the musical alter ego of American singer-keyboardist-songwriter Brian Hazard.

Biography

Hazard, the sole member of Color Theory, began studying the piano at the relatively late age of thirteen.
..... Click the link for more information.
color space. For example, Adobe RGB and sRGB are two different absolute color spaces, both based on the RGB model.

In the most generic sense of the definition above, color spaces can be defined without the use of a color model.
..... Click the link for more information.
Hue is one of the three main attributes of perceived color, in addition to lightness and chroma (or colorfulness). Hue is also one of the three dimensions in some colorspaces along with saturation, and brightness (also known as lightness or value).
..... Click the link for more information.
Intensity is a widely-used term, which can mean:

In colloquial use:
  • Strength
  • Amplitude
  • Level
  • Magnitude
In physics:
  • Intensity (physics), power per unit area (W/m2)

..... Click the link for more information.
This article or section is in need of attention from an expert on the subject.
Please help recruit one or [ improve this article] yourself. See the talk page for details.
..... Click the link for more information.
Optics (ὀπτική appearance or look in Ancient Greek) is a branch of physics that describes the behavior and properties of light and the interaction of light with matter.
..... Click the link for more information.
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 625–750 nm.
..... Click the link for more information.
RGB color model is an additive model in which red, green, and blue (often used in additive light models) are combined in various ways to reproduce other colors. The name of the model and the abbreviation ‘RGB’ come from the three primary colors, red, green, and blue and
..... Click the link for more information.
CMYK (short for cyan, magenta, yellow, and key (black), and often referred to as process color or four color) is a subtractive color model, used in color printing, also used to describe the printing process itself.
..... Click the link for more information.
Engineering is the applied science of acquiring and applying knowledge to design, analysis, and/or construction of works for practical purposes. The American Engineers' Council for Professional Development, also known as ECPD,[1] (later ABET [2]
..... Click the link for more information.
display device, also known as an information display is a device for visual or tactile presentation of images (including text) acquired, stored, or transmitted in various forms.
..... Click the link for more information.
perception is the process of acquiring, interpreting, selecting, and organizing sensory information. It is a task far more complex than was imagined in the 1950s and 1960s, when it was proclaimed that building perceiving machines would take about a decade, but, needless to say,
..... Click the link for more information.
An image is said to be burned when its original gamut considerably exceeds the target gamut, or when the result of processing considerably exceeds the image's gamut. Colloquially, an image is burned when it contains uniform blobs of color, black, or white where there should
..... Click the link for more information.
CIE 1931 XYZ color space (also known as CIE 1931 color space), created by the International Commission on Illumination (CIE) in 1931.

The human eye has receptors (called cone cells) for short (S), middle (M), and long (L) wavelengths.
..... Click the link for more information.
Monochrome comes from the two Greek words mono (μoνο, meaning "only" or "alone"), and chroma (χρωμα, meaning "colour"). A monochromatic object has a single colour.
..... Click the link for more information.
Eyes are organs of vision that detect light. Different kinds of light-sensitive organs are found in a variety of organisms. The simplest eyes do nothing but detect whether the surroundings are light or dark, while more complex eyes can distinguish shapes and colors.
..... Click the link for more information.
A phosphor is a substance that exhibits the phenomenon of phosphorescence (sustained glowing after exposure to light or energised particles such as electrons).

The chemical element phosphorus (Greek.
..... Click the link for more information.
Monochrome comes from the two Greek words mono (μoνο, meaning "only" or "alone"), and chroma (χρωμα, meaning "colour"). A monochromatic object has a single colour.
..... Click the link for more information.
In physics, wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek letter lambda (λ). Examples of wave-like phenonomena are light, water waves, and sound waves.
..... Click the link for more information.
laser is a mechanical device that produces coherent radiation. The term "laser" is an acronym: Light Amplification by Stimulated Emission of Radiation.
..... Click the link for more information.
In geometry, a convex polygon is a simple polygon whose interior is a convex set. The following properties of a simple polygon are all equivalent to convexity:
  • Every internal angle is at most 180 degrees.

..... Click the link for more information.
A laser video projector takes a video signal and modulates a laser beam in order to project a raster-based image. laser light shows use a vector-based system of rendering a pattern so are not appropriate for video projection.
..... Click the link for more information.


This article is copied from an article on Wikipedia.org - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the wikipedia encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.
Herod_Archelaus


page counter