Editing RGB color model (section)

===RGB and displays===
[[File:CRT color enhanced.png|right|thumb|250px|Cutaway rendering of a color CRT: '''1.'''&nbsp;Electron guns '''2.'''&nbsp;Electron beams '''3.'''&nbsp;Focusing coils '''4.'''&nbsp;Deflection coils '''5.'''&nbsp;Anode connection '''6.'''&nbsp;Mask for separating beams for red, green, and blue part of displayed image '''7.'''&nbsp;Phosphor layer with red, green, and blue zones '''8.'''&nbsp;Close-up of the phosphor-coated inner side of the screen]]
[[File:RGB color wheel 10.svg|thumb|right|250px|Color wheel with RGB pixels of the colors]]
[[File:RGB pixels on a CRT monitor.jpg|thumb|right|250px|RGB [[phosphor]] dots in a [[CRT monitor]]]]
[[File:RGB pixels.jpg|thumb|right|250px|RGB [[sub-pixel]]s in an LCD TV (on the right: an orange and a blue color; on the left: a close-up)]]

One common application of the RGB color model is the display of colors on a [[cathode-ray tube]] (CRT), [[liquid-crystal display]] (LCD), [[plasma display]], or [[OLED|organic light emitting diode]] (OLED) display such as a television, a computer's monitor, or a large scale screen. Each [[pixel]] on the screen is built by driving three small and very close but still separated RGB light sources. At common viewing distance, the separate sources are indistinguishable, which the eye interprets as a given solid color. All the pixels together arranged in the rectangular screen surface conforms the color image.

During [[digital image processing]] each pixel can be represented in the [[computer memory]] or interface hardware (for example, a ''[[display adapter|graphics card]]'') as [[binary number|binary]] values for the red, green, and blue color components. When properly managed, these values are converted into intensities or voltages via [[gamma correction]] to correct the inherent nonlinearity of some devices, such that the intended intensities are reproduced on the display.

The [[Quattron]] released by Sharp uses RGB color and adds yellow as a sub-pixel, supposedly allowing an increase in the number of available colors.

====Video electronics====
{{Main|Component video#RGB analog component video}}

RGB is also the term referring to 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. 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.<ref name="British Standard">{{cite book |url=http://fr.meric.free.fr/Articles/articlesba/stsurtvplat/Scart/BS_EN_50049-1%20Peritelevision%20connector.pdf |title=Domestic and similar electronic equipment interconnection requirements: Peritelevision connector |date=15 June 1998 |publisher=[[British Standards Institution]] |isbn=0580298604}}</ref><ref>{{Cite web |title=Composite video vs composite sync and Demystifying RGB video |url=https://www.retrogamingcables.co.uk/composite-video-vs-composite-sync |access-date=2022-10-24 |website=www.retrogamingcables.co.uk}}</ref> This signal is known as [[RGBS]] (4 [[BNC connector|BNC]]/[[RCA connector|RCA]] terminated cables exist as well), but it is directly compatible with [[RGBHV]] used for computer monitors (usually carried on 15-pin cables terminated with 15-pin [[D-sub]] or 5 BNC connectors), which carries separate horizontal and vertical sync signals.

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.

====Video framebuffer====
A [[framebuffer]] is a digital device for computers which stores data in the so-called ''video memory'' (comprising an array of [[Video RAM#Video DRAM (VRAM)|Video RAM]] or similar [[integrated circuit|chips]]). This data goes either to three [[digital-to-analog converter]]s (DACs) (for analog monitors), one per primary color or directly to digital monitors. Driven by [[software]], the [[central processing unit|CPU]] (or other specialized chips) write the appropriate [[byte]]s into the video memory to define the image. Modern systems encode pixel color values by devoting 8&nbsp;[[bit]]s to each of the R, G, and B components. RGB information can be either carried directly by the pixel bits themselves or provided by a separate '''[[color look-up table]]''' ('''CLUT''') if [[indexed color]] graphic modes are used.

A CLUT is a specialized [[random-access memory|RAM]] that stores R, G, and B values that define specific colors. Each color has its own address (index)—consider it as a descriptive reference number that provides that specific color when the image needs it. The content of the CLUT is much like a palette of colors. Image data that uses indexed color specifies addresses within the CLUT to provide the required R, G, and B values for each specific pixel, one pixel at a time. Of course, before displaying, the CLUT has to be loaded with R, G, and B values that define the palette of colors required for each image to be rendered. Some video applications store such palettes in [[PAL file]]s ([[Age of Empires (video game)|''Age of Empires'']] game, for example, uses over half-a-dozen<ref>By directory search</ref>) and can combine CLUTs on screen.

;RGB24 and RGB32
This indirect scheme restricts the number of available colors in an image CLUT—typically 256-cubed (8&nbsp;bits in three [[color channel]]s with values of 0–255)—although each color in the RGB24 CLUT table has only 8&nbsp;bits representing 256 codes for each of the R, G, and B primaries, making 16,777,216 possible colors. However, the advantage is that an indexed-color image file can be significantly smaller than it would be with only 8&nbsp;bits per pixel for each primary.

Modern storage, however, is far less costly, greatly reducing the need to minimize image file size. By using an appropriate combination of red, green, and blue intensities, many colors can be displayed. Current typical [[display adapter]]s use up to [[24-bit color|24&nbsp;bit]]s of information for each pixel: 8-bit per component multiplied by three components (see the [[#Numeric representations|Numeric representations]] section below (24&nbsp;bits&nbsp;=&nbsp;256<sup>3</sup>, each primary value of 8&nbsp;bits with values of 0–255). With this system, 16,777,216 (256<sup>3</sup> or 2<sup>24</sup>) discrete combinations of R, G, and B values are allowed, providing millions of different (though not necessarily distinguishable) hue, saturation and [[lightness (color)|lightness]] shades. Increased shading has been implemented in various ways, some formats such as [[Portable Network Graphics|.png]] and [[Truevision TGA|.tga]] files among others using a fourth [[grayscale]] color channel as a masking layer, often called '''RGB32'''.

For images with a modest range of brightnesses from the darkest to the lightest, 8&nbsp;bits per primary color provides good-quality images, but extreme images require more bits per primary color as well as the advanced display technology. For more information see [[High Dynamic Range]] (HDR) imaging.

====Nonlinearity====
{{Main|Gamma correction}}

In classic CRT devices, the brightness of a given point over the [[fluorescence|fluorescent]] screen due to the impact of accelerated [[electron]]s is not proportional to the voltages applied to the [[electron gun]] control grids, but to an expansive function of that voltage. The amount of this deviation is known as its [[gamma correction|gamma]] value (<math>\gamma</math>), the argument for a [[power law]] function, which closely describes this behavior. A linear response is given by a gamma value of 1.0, but actual CRT nonlinearities have a gamma value around 2.0 to 2.5.

Similarly, the intensity of the output on TV and computer display devices is not directly proportional to the R, G, and B applied electric signals (or file data values which drive them through digital-to-analog converters). On a typical standard 2.2-gamma CRT display, an input intensity RGB value of (0.5,&nbsp;0.5,&nbsp;0.5) only outputs about 22% of full brightness (1.0,&nbsp;1.0,&nbsp;1.0), instead of 50%.<ref>{{cite book | title = Digital Compositing for Film and Video | author = Steve Wright | publisher = Focal Press | isbn = 0-240-80760-X | year = 2006 | url = https://books.google.com/books?id=IpSRykrRamgC&q=display+gamma+2.2+0.5&pg=PA265 }}</ref> To obtain the correct response, a [[gamma correction]] is used in encoding the image data, and possibly further corrections as part of the [[color calibration]] process of the device. Gamma affects [[black-and-white]] TV as well as color. In standard color TV, broadcast signals are gamma corrected.