121-528: Y′UV , also written YUV , is the color model found in the PAL analogue color TV standard. A color is described as a Y′ component ( luma ) and two chroma components U and V. The prime symbol (') denotes that the luma is calculated from gamma-corrected RGB input and that it is different from true luminance . Today, the term YUV is commonly used in the computer industry to describe colorspaces that are encoded using YCbCr . In TV formats, color information (U and V)
242-535: A lookup table . Converting from RGB ↔ Munsell requires interpolating between that table's entries, and is extremely computationally expensive in comparison with converting from RGB ↔ HSL or RGB ↔ HSV which only requires a few simple arithmetic operations. The Swedish Natural Color System (NCS), widely used in Europe, takes a similar approach to the Ostwald bicone at right. Because it attempts to fit color into
363-433: A 2-degree field of view. In 1964, supplemental data for a 10-degree field of view were published. Note that the tabulated sensitivity curves have a certain amount of arbitrariness in them. The shapes of the individual X, Y and Z sensitivity curves can be measured with a reasonable accuracy. However, the overall luminosity function (which in fact is a weighted sum of these three curves) is subjective, since it involves asking
484-498: A K component is normally not needed or used in those media. A number of color models exist in which colors are fit into conic , cylindrical or spherical shapes, with neutrals running from black to white along a central axis, and hues corresponding to angles around the perimeter. Arrangements of this type date back to the 18th century, and continue to be developed in the most modern and scientific models. Different color theorists have each designed unique color solids . Many are in
605-414: A deep and neutral black impossible, the K (black ink) component, usually printed last, is needed to compensate for their deficiencies. Use of a separate black ink is also economically driven when a lot of black content is expected, e.g. in text media, to reduce simultaneous use of the three colored inks. The dyes used in traditional color photographic prints and slides are much more perfectly transparent, so
726-509: A familiarly shaped solid based on " phenomenological " instead of photometric or psychological characteristics, it suffers from some of the same disadvantages as HSL and HSV: in particular, its lightness dimension differs from perceived lightness, because it forces colorful yellow, red, green, and blue into a plane. In densitometry , a model quite similar to the hue defined above is used for describing colors of CMYK process inks. In 1953, Frank Preucil developed two geometric arrangements of hue,
847-498: A few more years because the original VGA cards were palette-driven just like EGA, although with more freedom than VGA, but because the VGA connectors were analog, later variants of VGA (made by various manufacturers under the informal name Super VGA) eventually added true-color. In 1992, magazines heavily advertised true-color Super VGA hardware. One common application of the RGB color model is
968-515: A fixed 1 / 2 in YCbCr § R'G'B' to Y'PbPr ). In Y′IQ, the UV plane is rotated by 33°. Y′UV was invented when engineers wanted color television in a black-and-white infrastructure. They needed a signal transmission method that was compatible with black-and-white (B&W) TV while being able to add color. The luma component already existed as the black and white signal; they added
1089-482: A fixed set of primary chromaticities, or particular set of red, green, and blue). Furthermore, the range of colors and brightnesses (known as the color gamut and color volume) of RGB (whether it be BT.601 or Rec. 709) is far smaller than the range of colors and brightnesses allowed by Y′UV. This can be very important when converting from Y′UV (or Y′CbCr) to RGB, since the formulas above can produce "invalid" RGB values – i.e., values below 0% or very far above 100% of
1210-404: A fourth greyscale color channel as a masking layer, often called RGB32 . For images with a modest range of brightnesses from the darkest to the lightest, eight 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. In classic CRT devices,
1331-677: A given RGB value differently, since the color elements (such as phosphors or dyes ) and their response to the individual red, green, and blue levels vary from manufacturer to manufacturer, or even in the same device over time. Thus an RGB value does not define the same color across devices without some kind of color management . Typical RGB input devices are color TV and video cameras , image scanners , and digital cameras . Typical RGB output devices are TV sets of various technologies ( CRT , LCD , plasma , OLED , quantum dots , etc.), computer and mobile phone displays, video projectors , multicolor LED displays and large screens such as
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#17327733505061452-399: A large part of the human color space and thus produce a large part of human color experiences. This is why color television sets or color computer monitors need only produce mixtures of red, green and blue light. See Additive color . Other primary colors could in principle be used, but with red, green and blue the largest portion of the human color space can be captured. Unfortunately there
1573-405: A luma component and two chroma components describing the color difference from gray. In all formats other than Y′IQ, each chroma component is a scaled version of the difference between red/blue and Y; the main difference lies in the scaling factors used, which is determined by color primaries and the intended numeric range (compare the use of U max and V max in § SDTV with BT.470 with
1694-489: A lumpy blob. Munsell's system became extremely popular, the de facto reference for American color standards—used not only for specifying the color of paints and crayons, but also, e.g., electrical wire, beer, and soil color—because it was organized based on perceptual measurements, specified colors via an easily learned and systematic triple of numbers, because the color chips sold in the Munsell Book of Color covered
1815-730: A measure of overall brightness or luminance. U and V are computed as scaled differences between Y′ and the B and R values. PAL (NTSC used YIQ , which is further rotated) standard defines the following constants, derived from BT.470 System M primaries and white point using SMPTE RP 177 (same constants called matrix coefficients were used later in BT.601 , although it uses 1/2 instead of 0.436 and 0.615): PAL signals in Y′UV are computed from R'G'B' (only SECAM IV used linear RGB) as follows: The resulting ranges of Y′, U, and V respectively are [0, 1], [− U max , U max ], and [− V max , V max ]. Inverting
1936-405: A meeting: one sees black lettering on a white background, even though the "black" has in fact not become darker than the white screen on which it is projected before the projector was turned on. The "black" areas have not actually become darker but appear "black" relative to the higher intensity "white" projected onto the screen around it. See also color constancy . The human tristimulus space has
2057-407: A neutral gray . Moving vertically in the color sphere, colors become lighter (toward the top) and darker (toward the bottom). At the upper pole, all hues meet in white; at the bottom pole, all hues meet in black. The vertical axis of the color sphere, then, is gray all along its length, varying from black at the bottom to white at the top. All pure (saturated) hues are located on the surface of
2178-407: A quarter as much color resolution compared to brightness resolution. Today, only high-end equipment processing uncompressed signals uses a chroma subsampling of 4:4:4 with identical resolution for both brightness and color information. The I and Q axes were chosen according to bandwidth needed by human vision, one axis being that requiring the most bandwidth, and the other (fortuitously at 90 degrees)
2299-423: A signal suitable for reception on old monochrome displays. In this case, the U and V are simply discarded. If displaying color, all three channels are used, and the original RGB information can be decoded. Another advantage of Y′UV is that some of the information can be discarded in order to reduce bandwidth . The human eye has fairly little spatial sensitivity to color: the accuracy of the brightness information of
2420-430: A test person whether two light sources have the same brightness, even if they are in completely different colors. Along the same lines, the relative magnitudes of the X, Y, and Z curves are arbitrarily chosen to produce equal areas under the curves. One could as well define a valid color space with an X sensitivity curve that has twice the amplitude. This new color space would have a different shape. The sensitivity curves in
2541-548: 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 files ( Age of Empires game, for example, uses over half-a-dozen ) and can combine CLUTs on screen. This indirect scheme restricts the number of available colors in an image CLUT—typically 256-cubed (8 bits in three color channels with values of 0–255)—although each color in
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#17327733505062662-602: A wide gamut and remained stable over time (rather than fading), and because it was effectively marketed by Munsell's Company . In the 1940s, the Optical Society of America made extensive measurements, and adjusted the arrangement of Munsell colors, issuing a set of "renotations". The trouble with the Munsell system for computer graphics applications is that its colors are not specified via any set of simple equations, but only via its foundational measurements: effectively
2783-674: Is a famous classification that organises various colors into a color solid based on hue, saturation and value. Other important color systems include the Swedish Natural Color System (NCS), the Optical Society of America 's Uniform Color Space (OSA-UCS), and the Hungarian Coloroid system developed by Antal Nemcsics from the Budapest University of Technology and Economics . Of those, the NCS
2904-493: Is a horse-shoe-shaped cone such as shown here (see also CIE chromaticity diagram below), extending from the origin to, in principle, infinity. In practice, the human color receptors will be saturated or even be damaged at extremely high light intensities, but such behavior is not part of the CIE color space and neither is the changing color perception at low light levels (see: Kruithof curve ). The most saturated colors are located at
3025-436: Is a specialized 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
3146-428: Is associated with a precise description of how the components are to be interpreted (viewing conditions, etc.), taking account of visual perception , the resulting set of colors is called " color space ." This article describes ways in which human color vision can be modeled, and discusses some of the models in common use. One can picture this space as a region in three-dimensional Euclidean space if one identifies
3267-927: Is based on the opponent-process color model, while the Munsell, the OSA-UCS and the Coloroid attempt to model color uniformity. The American Pantone and the German RAL commercial color-matching systems differ from the previous ones in that their color spaces are not based on an underlying color model. We also use "color model" to indicate a model or mechanism of color vision for explaining how color signals are processed from visual cones to ganglion cells. For simplicity, we call these models color mechanism models. The classical color mechanism models are Young – Helmholtz 's trichromatic model and Hering 's opponent-process model . Though these two theories were initially thought to be at odds, it later came to be understood that
3388-454: Is called the "CMY" or "CMYK" color space. The cyan ink absorbs red light but transmits green and blue, the magenta ink absorbs green light but transmits red and blue, and the yellow ink absorbs blue light but transmits red and green. The white substrate reflects the transmitted light back to the viewer. Because in practice the CMY inks suitable for printing also reflect a little bit of color, making
3509-464: Is either YUV, YIQ, or even CVBS ). Furthermore, NTSC and PAL encoded color signals in a manner that causes high bandwidth chroma and luma signals to mix with each other in a bid to maintain backward compatibility with black and white television equipment, which results in dot crawl and cross color artifacts. When the NTSC standard was created in the 1950s, this was not a real concern since the quality of
3630-402: Is formed by the sum of two primary colors of equal intensity: cyan is green+blue, magenta is blue+red, and yellow is red+green. Every secondary color is the complement of one primary color: cyan complements red, magenta complements green, and yellow complements blue. When all the primary colors are mixed in equal intensities, the result is white. The RGB color model itself does not define what
3751-526: 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, 0.5, 0.5) only outputs about 22% of full brightness (1.0, 1.0, 1.0), instead of 50%. To obtain
Y′UV - Misplaced Pages Continue
3872-422: Is given twice as many detectors as red and blue (ratio 1:2:1) in order to achieve higher luminance resolution than chrominance resolution. The sensor has a grid of red, green, and blue detectors arranged so that the first row is RGRGRGRG, the next is GBGBGBGB, and that sequence is repeated in subsequent rows. For every channel, missing pixels are obtained by interpolation in the demosaicing process to build up
3993-459: Is lightness, C * is chroma, and h * is hue angle. Officially, both CIELAB and CIELUV were created for their color difference metrics ∆ E * ab and ∆ E * uv , particularly for use defining color tolerances, but both have become widely used as color order systems and color appearance models, including in computer graphics and computer vision. For example, gamut mapping in ICC color management
4114-448: Is meant by red , green , and blue colorimetrically, and so the results of mixing them are not specified as absolute, but relative to the primary colors. 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 . The choice of primary colors is related to the physiology of the human eye ; good primaries are stimuli that maximize
4235-423: Is more red than green or blue. In turn this meant that when the U and V signals would be zero or absent, it would just display a grayscale image . If R and B were to have been used, these would have non-zero values even in a B&W scene, requiring all three data-carrying signals. This was important in the early days of color television, because old black and white TV signals had no U and V signals present, meaning
4356-567: Is more theoretically sophisticated and computationally complex than earlier models. Its aims are to fix several of the problems with models such as CIELAB and CIELUV, and to explain not only responses in carefully controlled experimental environments, but also to model the color appearance of real-world scenes. Its dimensions J (lightness), C (chroma), and h (hue) define a polar-coordinate geometry. There are various types of color systems that classify color and analyse their effects. The American Munsell color system devised by Albert H. Munsell
4477-428: Is no evidence those were ever used in practice (instead only actually described form of BT.709 is used, the YCbCr form): The primary advantage of luma/chroma systems such as Y′UV, and its relatives Y′IQ and YDbDr , is that they remain compatible with black and white analog television (largely due to the work of Georges Valensi ). The Y′ channel saves all the data recorded by black and white cameras, so it produces
4598-485: Is no exact consensus as to what loci in the chromaticity diagram the red, green, and blue colors should have, so the same RGB values can give rise to slightly different colors on different screens. RGB is a device-dependent color model: different devices detect or reproduce a given RGB value differently, since the color elements (such as phosphors or dyes ) and their response to the individual red, green, and blue levels vary from manufacturer to manufacturer, or even in
4719-491: 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. A framebuffer is a digital device for computers which stores data in the so-called video memory (comprising an array of Video RAM or similar chips ). This data goes either to three digital-to-analog converters (DACs) (for analog monitors), one per primary color or directly to digital monitors. Driven by software ,
4840-468: Is one of the most common ways to encode color in computing, and several different digital representations are in use. The main characteristic of all of them is the quantization of the possible values per component (technically a sample ) by using only integer numbers within some range, usually from 0 to some power of two minus one (2 − 1) to fit them into some bit groupings. Encodings of 1, 2, 4, 5, 8 and 16 bits per color are commonly found;
4961-448: Is represented by a cube using non-negative values within a 0–1 range, assigning black to the origin at the vertex (0, 0, 0), and with increasing intensity values running along the three axes up to white at the vertex (1, 1, 1), diagonally opposite black. An RGB triplet ( r , g , b ) represents the three-dimensional coordinate of the point of the given color within the cube or its faces or along its edges. This approach allows computations of
Y′UV - Misplaced Pages Continue
5082-415: Is simple. In particular, the Y' channels of both are linearly related to each other, both Cb and U are related linearly to (B-Y), and both Cr and V are related linearly to (R-Y). Color model In color science , 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. When this model
5203-414: Is the early-20th-century Munsell color system . Albert Munsell began with a spherical arrangement in his 1905 book A Color Notation , but he wished to properly separate color-making attributes into separate dimensions, which he called hue , value , and chroma , and after taking careful measurements of perceptual responses, he realized that no symmetrical shape would do, so he reorganized his system into
5324-1147: Is used. Following is the mathematical relationship between RGB space to HSI space (hue, saturation, and intensity: HSI color space ): I = R + G + B 3 S = 1 − 3 ( R + G + B ) min ( R , G , B ) H = cos − 1 ( ( R − G ) + ( R − B ) 2 ( R − G ) 2 + ( R − B ) ( G − B ) ) assuming G > B {\displaystyle {\begin{aligned}I&={\frac {R+G+B}{3}}\\S&=1\,-\,{\frac {3}{(R+G+B)}}\,\min(R,G,B)\\H&=\cos ^{-1}\left({\frac {(R-G)+(R-B)}{2{\sqrt {(R-G)^{2}+(R-B)(G-B)}}}}\right)\qquad {\text{assuming }}G>B\end{aligned}}} If B > G {\displaystyle B>G} , then H = 360 − H {\displaystyle H=360-H} . The RGB color model
5445-538: Is usually performed in CIELAB space, and Adobe Photoshop includes a CIELAB mode for editing images. CIELAB and CIELUV geometries are much more perceptually relevant than many others such as RGB, HSL, HSV, YUV/YIQ/YCbCr or XYZ, but are not perceptually perfect, and in particular have trouble adapting to unusual lighting conditions. The HCL color space seems to be synonymous with CIELCH. The CIE's most recent model, CIECAM02 (CAM stands for "color appearance model"),
5566-499: Is written in the different RGB notations as: In many environments, the component values within the ranges are not managed as linear (that is, the numbers are nonlinearly related to the intensities that they represent), as in digital cameras and TV broadcasting and receiving due to gamma correction, for example. Linear and nonlinear transformations are often dealt with via digital image processing. Representations with only 8 bits per component are considered sufficient if gamma correction
5687-500: The CIE 1931 color space the Rec. 709 color space is almost identical to Rec. 601 and covers 35.9%. In contrast to this UHDTV with Rec. 2020 covers a much larger area and thus its very own matrix was derived for YCbCr (no YUV/Y′UV, since decommissioning of analog TV). BT.709 defines these weight values: The U max and V max values are from above. The conversion matrices for analog form of BT.709 are these, but there
5808-449: The CPU (or other specialized chips) write the appropriate bytes into the video memory to define the image. Modern systems encode pixel color values by devoting eight bits 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
5929-612: The Enhanced Graphics Adapter (EGA) in 1984. The first manufacturer of a truecolor graphics card for PCs (the TARGA) was Truevision in 1987, but it was not until the arrival of the Video Graphics Array (VGA) in 1987 that RGB became popular, mainly due to the analog signals in the connection between the adapter and the monitor which allowed a very wide range of RGB colors. Actually, it had to wait
6050-582: The Jumbotron . Color printers , on the other hand, are not RGB devices, but subtractive color devices typically using the CMYK color model . To form a color with RGB, three light beams (one red, one green, and one blue) must be superimposed (for example by emission from a black screen or by reflection from a white screen). Each of the three beams is called a component of that color, and each of them can have an arbitrary intensity, from fully off to fully on, in
6171-497: The Numeric representations section below (24bits = 256 , each primary value of 8 bits with values of 0–255). With this system, 16,777,216 (256 or 2 ) discrete combinations of R, G, and B values are allowed, providing millions of different (though not necessarily distinguishable) hue, saturation and lightness shades. Increased shading has been implemented in various ways, some formats such as .png and .tga files among others using
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#17327733505066292-410: The black ), and full intensity of each gives a white ; the quality of this white depends on the nature of the primary light sources, but if they are properly balanced, the result is a neutral white matching the system's white point . When the intensities for all the components are the same, the result is a shade of gray, darker or lighter depending on the intensity. When the intensities are different,
6413-400: The x , y , and z axes with the stimuli for the long-wavelength ( L ), medium-wavelength ( M ), and short-wavelength ( S ) light receptors . The origin, ( S , M , L ) = (0,0,0), corresponds to black. White has no definite position in this diagram; rather it is defined according to the color temperature or white balance as desired or as available from ambient lighting. The human color space
6534-420: The "Preucil hue circle" and the "Preucil hue hexagon", analogous to our H and H 2 , respectively, but defined relative to idealized cyan, yellow, and magenta ink colors. The "Preucil hue error " of an ink indicates the difference in the "hue circle" between its color and the hue of the corresponding idealized ink color. The grayness of an ink is m / M , where m and M are the minimum and maximum among
6655-792: The August 1978 issue of Computer Graphics . In the same issue, Joblove and Greenberg described the HSL model—whose dimensions they labeled hue , relative chroma , and intensity —and compared it to HSV. Their model was based more upon how colors are organized and conceptualized in human vision in terms of other color-making attributes, such as hue, lightness, and chroma; as well as upon traditional color mixing methods—e.g., in painting—that involve mixing brightly colored pigments with black or white to achieve lighter, darker, or less colorful colors. The following year, 1979, at SIGGRAPH , Tektronix introduced graphics terminals using HSL for color designation, and
6776-551: The B&;W signal to color. It was necessary to assign a narrower bandwidth to the chrominance channel because there was no additional bandwidth available. If some of the luminance information arrived via the chrominance channel (as it would have if RB signals were used instead of differential UV signals), B&W resolution would have been compromised. Y′UV signals are typically created from RGB ( red , green and blue ) source. Weighted values of R, G, and B are summed to produce Y′,
6897-455: The CIE 1931 and 1964 xyz color space are scaled to have equal areas under the curves. Sometimes XYZ colors are represented by the luminance, Y, and chromaticity coordinates x and y , defined by: Mathematically, x and y are projective coordinates and the colors of the chromaticity diagram occupy a region of the real projective plane . Because the CIE sensitivity curves have equal areas under
7018-587: The Computer Graphics Standards Committee recommended it in their annual status report. These models were useful not only because they were more intuitive than raw RGB values, but also because the conversions to and from RGB were extremely fast to compute: they could run in real time on the hardware of the 1970s. Consequently, these models and similar ones have become ubiquitous throughout image editing and graphics software since then. Another influential older cylindrical color model
7139-402: The Munsell system. These efforts culminated in the 1976 CIELUV and CIELAB models. The dimensions of these models— ( L *, u *, v *) and ( L *, a *, b *) , respectively—are cartesian, based on the opponent process theory of color, but both are also often described using polar coordinates— ( L *, C * uv , h * uv ) and ( L *, C * ab , h * ab ) , respectively—where L *
7260-442: The NTSC (Y′IQ) and PAL systems, the chrominance signals had significantly narrower bandwidth than that for the luminance. Early versions of NTSC rapidly alternated between particular colors in identical image areas to make them appear adding up to each other to the human eye, while all modern analogue and even most digital video standards use chroma subsampling by recording a picture's color information at reduced resolution. Only half
7381-458: The RGB color model is described by indicating how much of each of the red, green, and blue is included. The color is expressed as an RGB triplet ( r , g , b ), each component of which can vary from zero to a defined maximum value. If all the components are at zero the result is black; if all are at maximum, the result is the brightest representable white. These ranges may be quantified in several different ways: For example, brightest saturated red
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#17327733505067502-425: The RGB color model is for the sensing, representation, and display of images in electronic systems, such as televisions and computers, though it has also been used in conventional photography and colored lighting . Before the electronic age , the RGB color model already had a solid theory behind it, based in human perception of colors . RGB is a device-dependent color model: different devices detect or reproduce
7623-689: The RGB24 CLUT table has only 8 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 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 adapters use up to 24-bits of information for each pixel: 8-bit per component multiplied by three components (see
7744-621: 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. This signal is known as RGBS (4 BNC / 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
7865-467: The U component vs. the V component. Not scaled matrix is used in Photo CD 's PhotoYCC. U and V are bipolar signals which can be positive or negative, and are zero for grays, whereas YCbCr usually scales all channels to either the 16–235 range or the 0–255 range, which makes Cb and Cr unsigned quantities which are 128 for grays. Nevertheless, the relationship between them in the standard case
7986-433: The UV signal to this as a solution. The UV representation of chrominance was chosen over straight R and B signals because U and V are color difference signals. In other words, the U and V signals tell the television to shift the color of a certain spot without altering its brightness. Or the U and V signals tell the monitor to make one color brighter at the cost of the other and by how much it should be shifted. The higher (or
8107-502: The X chromosome. One of these copies evolved to be sensitive to green light and constitutes our mid wavelength opsin. At the same time, our short wavelength opsin evolved from the ultraviolet opsin of our vertebrate and mammalian ancestors. Human red–green color blindness occurs because the two copies of the red and green opsin genes remain in close proximity on the X chromosome. Because of frequent recombination during meiosis, these gene pairs can get easily rearranged, creating versions of
8228-506: The Y′UV↔RGB conversion so that its member values are also slightly different. As a result, with SDTV and HDTV there are generally two distinct Y′UV representations possible for any RGB triple: a SDTV-Y′UV and an HDTV-Y′UV one. This means in detail that when directly converting between SDTV and HDTV, the luma (Y′) information is roughly the same but the representation of the chroma (U & V) channel information needs conversion. Still in coverage of
8349-415: The above transformation converts Y′UV to RGB: Equivalently, substituting values for the constants and expressing them as matrices gives these formulas for BT.470 System M (PAL): For small values of Y' it is possible to get R, G, or B values that are negative so in practice we clamp the RGB results to the interval [0,1] or more correctly clamp inside the Y'CbCr. In BT.470 a mistake was made because 0.115
8470-478: The amounts of idealized cyan, magenta, and yellow in a density measurement. The International Commission on Illumination (CIE) developed the XYZ model for describing the colors of light spectra in 1931, but its goal was to match human visual metamerism , rather than to be perceptually uniform, geometrically. In the 1960s and 1970s, attempts were made to transform XYZ colors into a more relevant geometry, influenced by
8591-400: The basis for the description below. Pure, saturated hues of equal brightness are located around the equator at the periphery of the color sphere. As in the color wheel, contrasting (or complementary) hues are located opposite each other. Moving toward the center of the color sphere on the equatorial plane, colors become less and less saturated, until all colors meet at the central axis as
8712-453: The brightness of a given point over the fluorescent screen due to the impact of accelerated electrons 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 value ( γ {\displaystyle \gamma } ), the argument for a power law function, which closely describes this behavior. A linear response
8833-496: The central vertical axis comprises the neutral , achromatic , or gray colors, ranging from black at lightness 0 or value 0, the bottom, to white at lightness 1 or value 1, the top. Most televisions, computer displays, and projectors produce colors by combining red, green, and blue light in varying intensities—the RGB additive primary colors . However, the relationship between the constituent amounts of red, green, and blue light and
8954-553: The color TV would just display it as B&W TV out of the box. In addition, black and white receivers could take the Y′ signal and ignore the U- and V-color signals, making Y′UV backward-compatible with all existing black-and-white equipment, input and output. If the color-TV standard wouldn't have used color difference signals, it could mean a color TV would make funny colors out of a B&W broadcast or it would need additional circuitry to translate
9075-448: The common chroma subsampling rate of 4:2:2, primarily for compatibility with previous analog video standards. This stream can be easily mixed into any output format needed. Y′UV is not an absolute color space . It is a way of encoding RGB information, and the actual color displayed depends on the actual RGB colorants used to display the signal. Therefore, a value expressed as Y′UV is only predictable if standard RGB colorants are used (i.e.
9196-416: The common color component between them, e.g. green as the common component between yellow and cyan, red as the common component between magenta and yellow, and blue-violet as the common component between magenta and cyan. There is no color component among magenta, cyan and yellow, thus rendering a spectrum of zero intensity: black. Zero intensity for each component gives the darkest color (no light, considered
9317-445: The complete image. Also, other processes used to be applied in order to map the camera RGB measurements into a standard color space as sRGB. In computing, an image scanner is a device that optically scans images (printed text, handwriting, or an object) and converts it to a digital image which is transferred to a computer. Among other formats, flat, drum and film scanners exist, and most of them support RGB color. They can be considered
9438-418: 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. In color television and video cameras manufactured before the 1990s, the incoming light was separated by prisms and filters into
9559-452: The curves, light with a flat energy spectrum corresponds to the point ( x , y ) = (0.333,0.333). The values for X , Y , and Z are obtained by integrating the product of the spectrum of a light beam and the published color-matching functions. RYB is a subtractive color model used in art and applied design in which red , yellow , and blue pigments are considered primary colors . The RYB color model relates specifically to color in
9680-684: The cyan plate, and so on. Before the development of practical electronic TV, there were patents on mechanically scanned color systems as early as 1889 in Russia . The color TV pioneer John Logie Baird demonstrated the world's first RGB color transmission in 1928, and also the world's first color broadcast in 1938, in London . In his experiments, scanning and display were done mechanically by spinning colorized wheels. The Columbia Broadcasting System (CBS) began an experimental RGB field-sequential color system in 1940. Images were scanned electrically, but
9801-455: 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 . 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 ). The difference in
9922-411: The display of colors on a cathode-ray tube (CRT), liquid-crystal display (LCD), plasma display , or 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
10043-462: 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 graphics card ) as 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
10164-512: The form of paint and pigment application in art and design. Other common color models include the light model (RGB) and the paint, pigment and ink CMY color model , which is much more accurate in terms of color gamut and intensity compared to the traditional RYB color model, the latter emerging in conjunction with the CMYK color model in the printing industry. This model was used for printing by Jacob Christoph Le Blon in 1725 and called it Coloritto or harmony of colouring , stating that
10285-411: The genes that do not have distinct spectral sensitivities. RGB color model The RGB color model is an additive color model in which the red , green and blue primary colors of 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. The main purpose of
10406-413: The horizontal resolution compared to the brightness information is kept (termed 4:2:2 chroma subsampling), and often the vertical resolution is also halved (giving 4:2:0). The 4:x:x standard was adopted due to the very earliest color NTSC standard which used a chroma subsampling of 4:1:1 (where the horizontal color resolution is quartered while the vertical is full resolution) so that the picture carried only
10527-431: The image sensor, whereas older drum scanners use a photomultiplier tube as the image sensor. Early color film scanners used a halogen lamp and a three-color filter wheel, so three exposures were needed to scan a single color image. Due to heating problems, the worst of them being the potential destruction of the scanned film, this technology was later replaced by non-heating light sources such as color LEDs . A color in
10648-460: The image was limited by the monitor equipment, not the limited-bandwidth signal being received. However today's modern television is capable of displaying more information than is contained in these lossy signals. To keep pace with the abilities of new display technologies, attempts were made since the late 1970s to preserve more of the Y′UV signal while transferring images, such as SCART (1977) and S-Video (1987) connectors. Instead of Y′UV, Y′CbCr
10769-518: 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. 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
10890-416: The intermediate optics, thereby reducing the size of home video cameras and eventually leading to the development of full camcorders . Current webcams and mobile phones with cameras are the most miniaturized commercial forms of such technology. Photographic digital cameras that use a CMOS or CCD image sensor often operate with some variation of the RGB model. In a Bayer filter arrangement, green
11011-444: The light under which we see them. In the additive model, if the resulting spectrum, e.g. of superposing three colors, is flat, white color is perceived by the human eye upon direct incidence on the retina. This is in stark contrast to the subtractive model, where the perceived resulting spectrum is what reflecting surfaces, such as dyed surfaces, emit. A dye filters out all colors but its own; two blended dyes filter out all colors but
11132-402: The lower when negative) the U and V values are, the more saturated (colorful) the spot gets. The closer the U and V values get to zero, the lesser it shifts the color meaning that the red, green and blue lights will be more equally bright, producing a grayer spot. This is the benefit of using color difference signals, i.e. instead of telling how much red there is to a color, it tells by how much it
11253-428: The luminance channel has far more impact on the image detail discerned than that of the other two. Understanding this human shortcoming, standards such as NTSC and PAL reduce the bandwidth of the chrominance channels considerably. (Bandwidth is in the temporal domain, but this translates into the spatial domain as the image is scanned out.) Therefore, the resulting U and V signals can be substantially "compressed". In
11374-593: The mechanisms responsible for color opponency receive signals from the three types of cones and process them at a more complex level. A widely accepted model is called the zone model. A symmetrical zone model compatible with the trichromatic theory, the opponent theory, and Smith's color transform model is called the decoding model Vertebrate animals were primitively tetrachromatic . They possessed four types of cones—long, mid, short wavelength cones, and ultraviolet sensitive cones. Today, fish, amphibians, reptiles and birds are all tetrachromatic. Placental mammals lost both
11495-414: 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 this difference is the basis of our perception of orange. Thus, the orange appearance of an object results from light from the object entering our eye and stimulating the different cones simultaneously but to different degrees. Use of
11616-497: The mid and short wavelength cones. Thus, most mammals do not have complex color vision—they are dichromatic but they are sensitive to ultraviolet light, though they cannot see its colors. Human trichromatic color vision is a recent evolutionary novelty that first evolved in the common ancestor of the Old World Primates. Our trichromatic color vision evolved by duplication of the long wavelength sensitive opsin , found on
11737-429: The minimum. However, true I and Q demodulation was relatively more complex, requiring two analog delay lines, and NTSC receivers rarely used it. However, this color modulation strategy is lossy , particularly because of crosstalk from the luma to the chroma-carrying wire, and vice versa, in analogue equipment (including RCA connectors to transfer a digital signal, as all they carry is analogue composite video , which
11858-511: The mixture. The RGB color model is additive in the sense that if light beams of differing color (frequency) are superposed in space their light spectra adds up, wavelength for wavelength, to make up a resulting, total spectrum. This is essentially opposite to the subtractive color model, particularly the CMY color model , which applies to paints, inks, dyes and other substances whose color depends on reflecting certain components (frequencies) of
11979-441: The offending colors such that they fall within the RGB gamut. Likewise, when RGB at a given bit depth is converted to YUV at the same bit depth, several RGB colors can become the same Y′UV color, resulting in information loss. Y′UV is often used as a term for YCbCr . However, while related, they are different formats with different scale factors; additionally, unlike YCbCr, Y’UV has historically used two different scale factors for
12100-418: The outer rim of the region, with brighter colors farther removed from the origin. As far as the responses of the receptors in the eye are concerned, there is no such thing as "brown" or "gray" light. The latter color names refer to orange and white light respectively, with an intensity that is lower than the light from surrounding areas. One can observe this by watching the screen of an overhead projector during
12221-470: The primitive (primary) colors are yellow, red and blue, while the secondary are orange, green and purple or violet . Media that transmit light (such as television) use additive color mixing with primary colors of red , green , and blue , each of which stimulates one of the three types of the eye's color receptors with as little stimulation as possible of the other two. This is called " RGB " color space. Mixtures of light of these primary colors cover
12342-634: The process of combining three color-filtered separate takes. To reproduce the color photograph, three matching projections over a screen in a dark room were necessary. The additive RGB model and variants such as orange–green–violet were also used in the Autochrome Lumière color plates and other screen-plate technologies such as the Joly color screen and the Paget process in the early twentieth century. Color photography by taking three separate plates
12463-624: The property that additive mixing of colors corresponds to the adding of vectors in this space. This makes it easy to, for example, describe the possible colors ( gamut ) that can be constructed from the red, green, and blue primaries in a computer display. One of the first mathematically defined color spaces is the CIE XYZ color space (also known as CIE 1931 color space), created by the International Commission on Illumination in 1931. These data were measured for human observers and
12584-400: The range (e.g., outside the standard 16–235 luma range (and 16–240 chroma range) for TVs and HD content, or outside 0–255 for standard definition on PCs). Unless these values are dealt with they will usually be "clipped" (i.e., limited) to the valid range of the channel affected. This changes the hue of the color, which is very undesirable, so it is therefore often considered better to desaturate
12705-469: The result is a colorized hue , more or less saturated depending on the difference of the strongest and weakest of the intensities of the primary colors employed. When one of the components has the strongest intensity, the color is a hue near this primary color (red-ish, green-ish, or blue-ish), and when two components have the same strongest intensity, then the color is a hue of a secondary color (a shade of cyan , magenta or yellow ). A secondary color
12826-460: The resulting color is unintuitive, especially for inexperienced users, and for users familiar with subtractive color mixing of paints or traditional artists’ models based on tints and shades. In an attempt to accommodate more traditional and intuitive color mixing models, computer graphics pioneers at PARC and NYIT developed the HSV model in the mid-1970s, formally described by Alvy Ray Smith in
12947-428: The same device over time. Thus an RGB value does not define the same color across devices without some kind of color management . It is possible to achieve a large range of colors seen by humans by combining cyan , magenta , and yellow transparent dyes/inks on a white substrate. These are the subtractive primary colors . Often a fourth ink, black , is added to improve reproduction of some dark colors. This
13068-409: The shape of a sphere , whereas others are warped three-dimensional ellipsoid figures—these variations being designed to express some aspect of the relationship of the colors more clearly. The color spheres conceived by Phillip Otto Runge and Johannes Itten are typical examples and prototypes for many other color solid schematics. The models of Runge and Itten are basically identical, and form
13189-436: 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. 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
13310-467: The sphere, varying from light to dark down the color sphere. All impure (unsaturated hues, created by mixing contrasting colors) comprise the sphere's interior, likewise varying in brightness from top to bottom. HSL and HSV are both cylindrical geometries, with hue, their angular dimension, starting at the red primary at 0°, passing through the green primary at 120° and the blue primary at 240°, and then wrapping back to red at 360°. In each geometry,
13431-448: The successors of early telephotography input devices, which were able to send consecutive scan lines as analog amplitude modulation signals through standard telephonic lines to appropriate receivers; such systems were in use in press since the 1920s to the mid-1990s. Color telephotographs were sent as three separated RGB filtered images consecutively. Currently available scanners typically use CCD or contact image sensor (CIS) as
13552-550: The system still used a moving part: the transparent RGB color wheel rotating at above 1,200 rpm in synchronism with the vertical scan. The camera and the cathode-ray tube (CRT) were both monochromatic . Color was provided by color wheels in the camera and the receiver. More recently, color wheels have been used in field-sequential projection TV receivers based on the Texas Instruments monochrome DLP imager. The modern RGB shadow mask technology for color CRT displays
13673-460: The three RGB primary colors feeding each color into a separate video camera tube (or pickup tube ). These tubes are a type of cathode-ray tube, not to be confused with that of CRT displays. With the arrival of commercially viable charge-coupled device (CCD) technology in the 1980s, first, the pickup tubes were replaced with this kind of sensor. Later, higher scale integration electronics was applied (mainly by Sony ), simplifying and even removing
13794-701: 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. The RGB color model is based on the Young–Helmholtz theory of trichromatic color vision , developed by Thomas Young and Hermann von Helmholtz in the early to mid-nineteenth century, and on James Clerk Maxwell 's color triangle that elaborated that theory ( c. 1860 ). The first experiments with RGB in early color photography were made in 1861 by Maxwell himself, and involved
13915-408: The total number of bits used for an RGB color is typically called the color depth . Since colors are usually defined by three components, not only in the RGB model, but also in other color models such as CIELAB and Y'UV , among others, then a three-dimensional volume is described by treating the component values as ordinary Cartesian coordinates in a Euclidean space . For the RGB model, this
14036-446: The usage of the same letter in luma (Y′), which approximates a perceptually uniform correlate of luminance. Likewise, U and V were chosen to differentiate the U and V axes from those in other spaces, such as the x and y chromaticity space. See the equations below or compare the historical development of the math. The scope of the terms Y′UV, YUV, YCbCr, YPbPr, etc., is sometimes ambiguous and overlapping. All these formats are based on
14157-425: Was added separately via a subcarrier so that a black-and-white receiver would still be able to receive and display a color picture transmission in the receiver's native black-and-white format, with no need for extra transmission bandwidth. As for etymology, Y, Y′, U, and V are not abbreviations. The use of the letter Y for luminance can be traced back to the choice of XYZ primaries. This lends itself naturally to
14278-665: Was patented by Werner Flechsig in Germany in 1938. Personal computers of the late 1970s and early 1980s, such as the Apple II and VIC-20 , use composite video . The Commodore 64 and the Atari 8-bit computers use S-Video derivatives. IBM introduced a 16-color scheme (four bits—one bit each for red, green, blue, and intensity) with the Color Graphics Adapter (CGA) for its IBM PC in 1981, later improved with
14399-502: Was used as the standard format for (digital) common video compression algorithms such as MPEG-2 . Digital television and DVDs preserve their compressed video streams in the MPEG-2 format, which uses a fully defined Y′CbCr color space, although retaining the established process of chroma subsampling. Cinepak , a video codec from 1991, used a modified YUV 4:2:0 colorspace. The professional CCIR 601 digital video format also uses Y′CbCr at
14520-521: Was used by other pioneers, such as the Russian Sergey Prokudin-Gorsky in the period 1909 through 1915. Such methods lasted until about 1960 using the expensive and extremely complex tri-color carbro Autotype process. When employed, the reproduction of prints from three-plate photos was done by dyes or pigments using the complementary CMY model, by simply using the negative plates of the filtered takes: reverse red gives
14641-514: Was used instead of 0.114 for blue and 0.493 was the result instead of 0.492. In practice that did not affect the decoders because the approximation 1/2.03 was used. For HDTV the ATSC decided to change the basic values for W R and W B compared to the previously selected values in the SDTV system. For HDTV these values are provided by Rec. 709 . This decision further impacted on the matrix for
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