A representation of additive color mixing. Projection of primary color lights on a screen shows secondary colors where two overlap; the combination of all three of red, green, and blue in appropriate intensities makes white.

The RGB color model is an additive color model in which red, green, and blue light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three additive primary colors, red, green, and blue. In astronomy, stellar evolution is the sequence of radical changes that a star undergoes during its lifetime (the time in which it emits light and heat). ... According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ... Image File history File links AdditiveColor. ... Image File history File links AdditiveColor. ... This article is about colors. ... Additive color mixing: adding red to green yields yellow; adding yellow to blue yields white. ... For other uses, see Red (disambiguation). ... For other uses, see Green (disambiguation). ... For other uses, see Blue (disambiguation). ... Color is an important part of the visual arts. ... This article is about colors. ...

The term RGBA is also used to mean Red, Green, Blue, Alpha. This is not a different color model, but a representation; the Alpha is used for transparency.

The RGB color model itself does not define what is meant by ‘red’, ‘green’ and ‘blue’ colorimetrically, and so the results of mixing them are not specified as exact, but relative. A 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 (e. ...

When the exact chromaticities of the red, green, and blue primaries are defined, the color model then becomes an absolute color space, such as sRGB or Adobe RGB; see RGB color spaces for more details. Chromaticity is the quality of a color as determined by its purity and dominant wavelength. ... An absolute color space is a color space in which colors are unambiguous, where they do not depend on any external factors. ... CIE 1931 xy chromaticity diagram showing the gamut of the sRGB color space and location of the primaries. ... The Adobe RGB color space is an RGB color space developed by Adobe Systems in 1998. ... An RGB color space is any additive color space based on the RGB color model. ...

This article discusses concepts common to all the different RGB color spaces that use the RGB color model, which are used in one implementation or another historically in color image producing electronics technology.

An RGB image, along with its separate R, G and B components; Note that the white snow consists of strong red, green and blue; the brown barn is composed of strong red and green with little blue; the dark green grass consists of strong green with little red or blue; and the light blue sky is composed of strong blue and moderately strong red and green.

Image File history File links Download high resolution version (1600x4780, 1056 KB) Summary This takes an image ( Image:Barns grand tetons. ... Image File history File links Download high resolution version (1600x4780, 1056 KB) Summary This takes an image ( Image:Barns grand tetons. ...

Additive primary colors

The choice of 'primary' colors is related to the physiology of the human eye; good primaries are stimuli that maximize the difference between the responses of the cone cells of the human retina to light of different wavelengths, and that thereby make a large color triangle.^[1] Normalised absorption spectra of human cone (S,M,L) and rod (R) cells Cone cells, or cones, are cells in the retina which only function in relatively bright light. ... For other uses, see Eye (disambiguation). ...

The normal three kinds of light-sensitive photoreceptor cells in the human eye (cone cells) respond most to yellow (long wavelength or L), green (medium or M) and violet (short or S) light (peak wavelengths near 570 nm, 540 nm and 440 nm respectively^[1]). The difference in the signals received from the three kinds allows the brain to differentiate a wide gamut of different colors, while being most sensitive (overall) to yellowish-green light and to differences between hues in the green-to-orange region. This article is about cellular photoreceptors. ... In color reproduction, including computer graphics and photography, the gamut, or color gamut (pronounced ), is a certain complete subset of colors. ... An image with the hues cyclically shifted The hues in the image of this Painted Bunting are cyclically rotated with time. ...

As an example, suppose that light in the orange range of wavelengths (approximately 577 nm to 597 nm) enters the eye and strikes the retina. Light of these wavelengths would activate both the medium and long wavelength cones of the retina, but not equally—the long-wavelength cells will respond more. The difference in the response can be detected by the brain and associated with the concept that the light is 'orange'. In this sense, the orange appearance of objects is simply the result of light from the object entering our eye and stimulating the relevant kinds of cones simultaneously but to different degrees.

Use of the three primary colors is not sufficient to reproduce all colors; only colors within the color triangle defined by the chromaticities of the primaries can be reproduced by additive mixing of non-negative amounts of those colors of light.^[1] Chromaticity is the quality of a color as determined by its purity and dominant wavelength. ...

A set of primary colors, such as the sRGBprimaries, define a color triangle; only colors within this triangle can be reproduced by mixing the primary colors. Colors outside the color triangle are therefore shown here as gray. The primaries and the D65 white point of sRGB are shown.

Image File history File links CIExy1931_srgb_gamut. ... Image File history File links CIExy1931_srgb_gamut. ... The title given to this article is incorrect due to technical limitations. ... One of the standard illuminants defined by the International Commission on Illumination (CIE) inside a series of illuminants called D series that try to portrait standard illuminanting conditions at open air in different parts of the world. ... A white point is one of a number of reference illuminants used in colorimetry which serve to define the color white. Depending on the application, different definitions of white are needed to give acceptable results. ...

RGB and displays

One common application of the RGB color model is the display of colors on a cathode ray tube, liquid crystal display or plasma display, such as a television or a computer’s monitor. Each pixel on the screen can be represented in the computer or interface hardware (for example, a ‘graphics card’) as values for red, green, and blue. These values are converted into intensities or voltages via gamma correction, such that the intended intensities are reproduced on the display. Cathode ray tube employing electromagnetic focus and deflection Cutaway rendering of a color CRT: 1. ... LCD redirects here. ... An example of a plasma display Composition of plasma display panel A plasma display panel (PDP) is a type of flat panel display now commonly used for large TV displays (typically above 37-inch or 940 mm). ... This example shows an image with a portion greatly enlarged, in which the individual pixels are rendered as little squares and can easily be seen. ... Example of CRT gamma correction Plot of the sRGB standard gamma-expansion nonlinearity (red), and its local gamma value, slope in log–log space (blue). ...

By using an appropriate combination of red, green, and blue intensities, many colors can be represented. Typical display adapters in 2007 use up to 24 bits of information for each pixel. This is usually apportioned with 8 bits each for red, green and blue, giving a range of 256 possible values, or intensities, for each hue. With this system, 16,777,216 (256³ or 2²⁴) discrete combinations of hue, saturation, and lightness can be specified, though not necessarily distinguished. Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... In computer architecture, 24-bit is an adjective used to describe integers, memory addresses or other data units that are at most 24 bits (3 octets) wide, or to describe CPU and ALU architectures based on registers, address buses, or data buses of that size. ... An image with the hues cyclically shifted The hues in the image of this Painted Bunting are cyclically rotated with time. ... It has been suggested that this article or section be merged with Chromaticity. ... Lightness is a property of a color, or a dimension of a color space, that correlates with how bright or luminous a color is. ...

Video electronics

RGB is a type of component video signal used in the video electronics industry. It consists of three signals—red, green and blue—carried on three separate cables/pins. Extra cables are sometimes needed to carry synchronizing signals. RGB signal formats are often based on modified versions of the RS-170 and RS-343 standards for monochrome video. This type of video signal is widely used in Europe since it is the best quality signal that can be carried on the standard SCART connector. Outside Europe, RGB is not very popular as a video signal format; S-Video takes that spot in most non-European regions. However, almost all computer monitors around the world use RGB. Three cables, each with RCA plugs at both ends, are often used to carry analog component video Component video is a video signal that has been split into two or more components. ... This article does not cite any references or sources. ... For other uses, see Europe (disambiguation). ... This article or section is in need of attention from an expert on the subject. ... S-Video (also known as Y/C) is a baseband analog video format offering a higher quality signal than composite video, but a lower quality than RGB and component video. ...

RGB pixels in an LCD TV (on the right: an orange and a blue color; on the left: a close-up of pixels)

Image File history File links RGB_pixels. ... Image File history File links RGB_pixels. ...

Nonlinearity

Due to gamma correction, the intensity of the color output on computer display devices is normally not directly proportional to the R, G, and B values in image files. That is, even though a value of 0.5 is very close to halfway between 0 and 1.0 (full intensity), the light intensity of a computer display device when displaying (0.5, 0.5, 0.5) is normally (on a standard 2.2-gamma CRT/LCD) only about 22% of that when displaying (1.0, 1.0, 1.0), instead of at 50%.^[2] Example of CRT gamma correction Plot of the sRGB standard gamma-expansion nonlinearity (red), and its local gamma value, slope in log–log space (blue). ...

Professional color calibration

Proper reproduction of colors in professional environments requires extensive color calibration of all the devices involved in the production process. This results in several transparent conversions between device-dependent color spaces during a typical production cycle in order to ensure color consistency throughout the process. Along with the creative processing, all such interventions on digital images inherently damage it by reducing its gamut. Therefore the denser the gamut of the original digitized image, the more processing it can support without visible degradation. Professional devices and software tools allow for 48 bpp (bits per pixel) images to be manipulated (16 bits per channel) in order to increase the density of the gamut. This article does not cite any references or sources. ... A comparison of different color spaces. ... In color reproduction, including computer graphics and photography, the gamut, or color gamut (pronounced ), is a certain complete subset of colors. ...

Representations

Main article: Bitmap

This article is about the storage organization of raster images. ...

Numeric representations

The RGB color model mapped to a cube (with cut-away shown)

A color in the RGB color model can be described by indicating how much of each of the red, green, and blue is included. Each can vary between the minimum (fully dark) and maximum (full intensity). If all the colors are at minimum the result is black. If all the colors at maximum, the result is a white. Image File history File links RGBCube_b. ... Image File history File links RGBCube_b. ...

These colors may be quantified in several different ways:

• Color scientists often place colors in the range 0 (minimum) through 1 (maximum). Many color formulae take these values. For instance, full intensity red using this convention is 1, 0, 0 for Red, Green, and Blue.
• The color values may be written as percentages, from 0% (minimum) to 100% (maximum). To convert from the range 0 to 1, see percentage. Full intensity red, using this notation, is 100%, 0%, 0%.
• The color values may be written as numbers in the range 0 to 255. This is commonly found in computer representations, where programmers have found it convenient to store each color value in one 8-bit byte. This convention has become so widespread that some writers now consider the range 0 to 255 an assumption and fail to give a context for their values. Full intensity red, using this scheme, is 255, 0, 0. This range of values is not proportional to the others, but rather a nonlinear gamma-encoded scale.
• That same range, 0 through 255, is sometimes written in hexadecimal – full intensity red becomes FF, 00, 00, which can be contracted to #FF0000 (a convention used by HTML).

The percent sign. ... In computer science a byte (pronounced bite) is a unit of measurement of information storage, most often consisting of eight bits. ... Example of CRT gamma correction Plot of the sRGB standard gamma-expansion nonlinearity (red), and its local gamma value, slope in log–log space (blue). ... In mathematics and computer science, hexadecimal, base-16, or simply hex, is a numeral system with a radix, or base, of 16, usually written using the symbols 0–9 and A–F, or a–f. ...

24-bit representation

RGB values encoded in 24 bits per pixel (bpp) are specified using three 8-bit unsigned integers (0 through 255) representing the intensities of red, green, and blue (usually in that order). For example, the following image shows the three "fully saturated" faces of an RGB cube, unfolded into a plane:

(0, 0, 0) is black (255, 255, 255) is white (255, 0, 0) is red (0, 255, 0) is green (0, 0, 255) is blue (255, 255, 0) is yellow (0, 255, 255) is cyan (255, 0, 255) is magenta	yellow (255,255,0)	green (0,255,0)	cyan (0,255,255)
	red (255,0,0)		blue (0,0,255)
		red (255,0,0)	magenta (255,0,255)

The above definition uses a convention known as full-range RGB. Color values are also often considered to be in the range 0.0 through 1.0, which may be mapped to other digital encodings. This article is about the color. ... This article is about the color. ... For other uses, see Red (disambiguation). ... For other uses, see Green (disambiguation). ... For other uses, see Blue (disambiguation). ... A yellow Tulip. ... Cyan (from Greek κυανοs, meaning blue) may be used as the name of any of a number of a range of colors in the blue/green part of the spectrum. ... Magenta is a color made up of equal parts of red and blue light. ... Image File history File links RGBR.png File links The following pages link to this file: RGB color model ...

Full-range RGB using eight bits per primary can represent up to 256 shades of white-grey-black, two hundred and fifty-five shades of red, green, and blue (and equal mixtures of those), but fewer shades of other hues. The 256 levels do not represent equally spaced intensities, due to gamma correction. Example of CRT gamma correction Plot of the sRGB standard gamma-expansion nonlinearity (red), and its local gamma value, slope in log–log space (blue). ...

Typically, RGB for digital video is not full range. Instead, video RGB uses a convention with scaling and offsets such that (16, 16, 16) is black, (235, 235, 235) is white, etc. For example, these scalings and offsets are used for the digital RGB definition in CCIR 601. Digital video is a type of video recording system that works by using a digital, rather than analog, of the video signal. ... This article is about the color. ... This article is about the color. ... CCIR 601 is the old name of a standard published by the CCIR (now ITU-R) for encoding interlaced analogue video signals in digital form. ...

Memory space

The amount of memory space used by an uncompressed image is specified by the number of pixels in the image and the color depth to which each pixel is specified. In a 24-bit image, each pixel is specified by a 24-bit allocation of memory, so the amount of space required in bits is 24 × the number of pixels. To calculate the memory required in bytes, the resulting number should be divided by 8 (8 bits in a byte).

E.g. A 24-bit image 640 × 480 pixels in size

24 × 640 × 480 = 7,372,800 bits

7,372,800 / 8 = 921,600 bytes

16-bit mode

Main article: Highcolour

There is also a 16 bpp mode (sometimes called Highcolor), in which there are either 5 bits per color, called 555 mode, or an extra bit for green (because the green component contributes most to the brightness of a color in the human eye), called 565 mode. Highcolour (or Hicolour, Highcolor, Hicolor, Thousands on a Macintosh) graphics is a method of storing image information in a computers memory such that each pixel is represented by two bytes. ... This article is about the complexity class. ... Highcolour (or Hicolour, Highcolor, Hicolor, Thousands on a Macintosh) graphics is a method of storing image information in a computers memory such that each pixel is represented by two bytes. ...

32-bit mode

The so-called 32 bpp mode is almost always identical in precision to the 24 bpp mode; there are still only eight bits per component, and the eight extra bits are often not used at all. The reason for the existence of the 32 bpp mode is the higher speed at which most modern hardware can access data that is aligned to byte addresses evenly divisible by a power of two, compared to data not so aligned. The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... In computer science a byte (pronounced bite) is a unit of measurement of information storage, most often consisting of eight bits. ...

Some graphics hardware allows the unused byte to be used as an 8-bit paletted overlay. A certain palette entry (often 0 or 255) is designated as being transparent, i.e., where the overlay is this value the truecolor image is shown. Otherwise the overlay value is looked up in the palette and used. This allows for GUI elements (such as menus or the mouse cursor) or information to be overlayed over a truecolor image without modifying it. When the overlay needs to be removed, it is simply cleared to the transparent value and the truecolor image is displayed again. This feature was often found on graphics hardware for Unix workstations in the 90s and later on some PC graphics cards (most notably those by Matrox). However, PC graphics cards (and the systems they are used in) now have plentiful memory to use as a backing store and this feature has mostly disappeared. A palette, in computer graphics, is a designated subset of the total range of colors supported by a computer graphics system. ... GUI can refer to the following: GUI is short for graphical user interface, a term used to describe a type of interface in computing. ... Filiation of Unix and Unix-like systems Unix (officially trademarked as UNIX®, sometimes also written as or ® with small caps) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. ... Matrox Electronic Systems Ltd is a Canadian company based in Dorval, Quebec, which produces video card components and equipment for personal computers. ...

48-bit mode (sometimes also called 16-bit mode)

"16-bit mode" can also refer to 16 bit per component, resulting in 48 bpp. This mode makes it possible to represent 65536 tones of each color component instead of 256. This is primarily used in professional image editing, like Adobe Photoshop for maintaining greater precision when a sequence of more than one image filtering algorithms is used on the image. With only 8 bit per component, rounding errors tend to accumulate with each filtering algorithm that is employed, distorting the end result. This article is about the complexity class. ... Adobe Photoshop is a bitmap graphics editor (with some text and vector graphics capabilities) published by Adobe Systems. ... A round-off error is the difference between the calculated approximation of a number and its exact mathematical value. ...

RGBA

With the need for compositing images came a variant of RGB which includes an extra 8-bit channel for transparency, thus resulting in a 32 bpp format. The transparency channel is commonly known as the alpha channel, so the format is named RGBA. Note that since it does not change anything in the RGB model, RGBA is not a distinct color model, it is only a file format which integrates transparency information along with the color information in the same file. This allows for alpha blending of the image over another, and is a feature of the PNG format. (Note: RGBA is not the only method to have transparency in graphics. See Transparency (graphic) for alternatives.) In computer graphics, alpha compositing is often useful to render image elements in separate passes, and then combine the resulting multiple 2D images into a single, final image in a process called compositing. ... RGBA stands for Red Green Blue Alpha. ... Alpha blending is a convex combination of two colors allowing for transparency effects in computer graphics. ... PNG (Portable Network Graphics), sometimes pronounced as ping, is a relatively new bitmap image format that is becoming popular on the World Wide Web and elsewhere. ... Transparency is possible in a number of graphics file formats. ...

Digital cameras that use a CMOS or CCD image sensor often operate with the RGB system; the sensor can have a grid of red, green, and blue detectors arranged so that the first row is RGRGRGRG and the next is GBGBGBGB and so on. In a Bayer filter, green is given more detectors than red and blue in order to achieve higher luminance resolution than chrominance resolution. Demoasicing and matrixing processes are required to map the camera RGB measurements into a standard RGB color space. For other uses, see CMOS (disambiguation). ... CCD can stand for: Cafe Coffee Day, a chain of coffee shops in India Charge-coupled device, an electronic light sensor used in digital cameras Colony Collapse Disorder, a mysterious die-off of commercial honeybees Confraternity of Christian Doctrine, a Catholic association devoted to teaching religion Carbonate Compensation Depth, a... A dismantled USB webcam, with and without a lens over its (Bayer format) image sensor. ... The Bayer arrangement of color filters on the pixel array of an image sensor Front page of Dr. Bryce Bayers 1976 patent on the Bayer pattern filter mosaic, showing his terminology of luminance-sensitive and chrominance-sensitive elements A Bayer filter mosaic is a color filter array (CFA) for... Luminance (also called luminosity) is a photometric measure of the density of luminous intensity in a given direction. ... Chrominance (chroma for short) comprises the two components of a television signal that encode color information. ... An RGB color space is any additive color space based on the RGB color model. ...

Colors in web-page design

Main article: Web colors

Colors used in web-page design are commonly specified using RGB; see web colors for an explanation of how colors are used in HTML and related languages. Initially, the limited color depth of most video hardware led to a limited color palette of 216 RGB colors, defined by the Netscape Color Cube. However, with the predominance of 24-bit displays, the use of the full 16.7 million colors of the HTML RGB color code no longer poses problems for most viewers. Web colors are colors used in designing web pages, and the methods for describing and specifying those colors. ... Web colors are colors used in designing web pages, and the methods for describing and specifying those colors. ... HTML, short for Hypertext Markup Language, is the predominant markup language for web pages. ...

In short, the web-safe color palette consists of the 216 combinations of red, green and blue where each color can take one of six values (in hexadecimal): #00, #33, #66, #99, #CC or #FF (based on the 0 to 255 range for each value discussed above). Clearly, 6³ = 216. These hexadecimal values = 0, 51, 102, 153, 204, 255 in decimal, which = 0%, 20%, 40%, 60%, 80%, 100% in terms of intensity. This seems fine for splitting up 216 colors into a cube of dimension 6. However, lacking gamma correction, the perceived intensity on a standard 2.5 gamma CRT / LCD is only: 0%, 2%, 10%, 28%, 57%, 100%. See the actual web safe color palette for a visual confirmation that the majority of the colors produced are very dark, or see Xona.com Color List for a side by side comparison of proper colors next to their equivalent lacking proper gamma correction. Web colors are colors used in designing web pages, and the methods for describing and specifying those colors. ... In mathematics and computer science, hexadecimal, base-16, or simply hex, is a numeral system with a radix, or base, of 16, usually written using the symbols 0–9 and A–F, or a–f. ... Example of CRT gamma correction Plot of the sRGB standard gamma-expansion nonlinearity (red), and its local gamma value, slope in log–log space (blue). ... Web colors are colors used in designing web pages, and the methods for describing and specifying those colors. ...

The RGB color model for HTML was formally adopted as an Internet standard in HTML 3.2, however it had been in use for some time before that.

History of RGB color model

The RGB color model is based on the Young–Helmholtz theory of trichromatic color vision, and on Maxwell's color triangle that elaborated that theory. The Young–Helmholtz theory (proposed in the 19th century by Thomas Young and Hermann von Helmholtz) is a theory of trichromatic color vision - the manner in which the photoreceptors in the eyes of humans and other primates work to enable color vision. ... Normalised absorption spectra of human cone (S,M,L) and rod (R) cells Trichromatic color vision is the ability of humans and some other animals to see different colors, mediated by interactions among three types of color-sensing cone cells. ... James Clerk Maxwell (13 June 1831 – 5 November 1879) was a Scottish mathematician and theoretical physicist from Edinburgh, Scotland, UK. His most significant achievement was aggregating a set of equations in electricity, magnetism and inductance — eponymously named Maxwells equations — including an important modification (extension) of the Ampères...

The use of the RGB color model as the standard for presentation of color on the Internet has its roots in the 1953 RCA color-TV standards and in Edwin Land's use of an RGB standard in the Land/Polaroid camera.^[clarify] Year 1953 (MCMLIII) was a common year starting on Thursday (link will display full calendar) of the Gregorian calendar. ... RCA, formerly an acronym for the Radio Corporation of America, is now a trademark owned by Thomson SA through RCA Trademark Management S.A., a company owned by Thomson. ... Edwin Herbert Land (May 7, 1909 – March 1, 1991) was an American scientist and inventor. ... Polaroid Corporation was founded in 1937 by Edwin H. Land. ...

See also

• Gamma correction
• Additive color
• List of colors
• Color banding
• Bits per pixel
• SCART connector
• Color theory

Example of CRT gamma correction Plot of the sRGB standard gamma-expansion nonlinearity (red), and its local gamma value, slope in log–log space (blue). ... Additive color mixing: adding red to green yields yellow; adding yellow to blue yields white. ... The following is a partial list of colors with associated articles. ... Color Banding Illustrated Color banding is a problem of inaccurate color presentation in computer graphics. ... Color depth is a computer graphics term describing the number of bits used to represent the color of a single pixel in a bitmapped image or video frame buffer. ... This article or section is in need of attention from an expert on the subject. ... In the arts of painting, graphic design, and photography, color theory is a body of practical guidance to color mixing and the visual impact of specific color combinations. ...

References

Mike Cowlishaw is an IBM Fellow based at IBM UK’s Warwick location, a Visiting Professor at the Department of Computer Science at the University of Warwick, and an elected Fellow of the Royal Academy of Engineering (roughly the equivalent of the NAE in the USA). ... PDF is an abbreviation with several meanings: Portable Document Format Post-doctoral fellowship Probability density function There also is an electronic design automation company named PDF Solutions. ...

External links

• Demonstrative color conversion applet