1.
Cyan
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It is evoked by light with a predominant wavelength of between 490–520 nm, between the wavelengths of blue and green. In the subtractive color system, or CMYK, which can be overlaid to produce all colors in paint and color printing, cyan is one of the colors, along with magenta, yellow. In the additive color system, or RGB color model, used to all the colors on a computer or television display, cyan is made by mixing equal amounts of green. Cyan is the complement of red, it can be made by the removal of red from white light, mixing red light and cyan light at the right intensity will make white light. The web color cyan is synonymous with aqua, other colors in the cyan color range are teal, turquoise, electric blue, aquamarine, and others described as blue-green. Its name is derived from the Ancient Greek κύανος, transliterated kyanos, meaning blue, dark blue enamel. It was formerly known as blue or cyan-blue, and its first recorded use as a color name in English was in 1879. Further origins of the name can be traced back to a dye produced from the cornflower. In most languages, cyan is not a color term. Reasons for why cyan is not linguistically acknowledged as a color term can be found in the frequent lack of distinction between blue and green in many languages. The web color cyan shown at right is a color in the RGB color model. In X11 colors, this color is called both cyan and aqua, in the HTML color list, this same color is called aqua. The web colors are more vivid than the used in the CMYK color system. To reproduce the web color cyan in inks, it is necessary to add some white ink to the printers cyan below, so when it is reproduced in printing, it is not a primary subtractive color. It is called aqua because it is a commonly associated with water. Cyan is also one of the inks used in four-color printing, along with magenta, yellow, and black. While both the secondary and the subtractive primary are called cyan, they can be substantially different from one another. Cyan printing ink can be saturated or less saturated than the RGB secondary cyan, depending on what RGB color space
2.
SRGB
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SRGB is the standard RGB color space created cooperatively by HP and Microsoft in 1996 for use on monitors, printers and the Internet, and subsequently standardized by the IEC as IEC 61966-2-1,1999. It is often used as the color space for images that do not contain any color space information. This specification allowed sRGB to be displayed on typical CRT monitors of the time. SRGB defines the chromaticities of the red, green, and blue primaries, the gamut of chromaticities that can be represented in sRGB is the color triangle defined by these primaries. SRGB also defines a transformation between the intensity of these primaries and the actual number stored. The curve is similar to the response of a CRT display. It is more important to replicate this curve than the primaries to get correct display of an sRGB image and this nonlinear conversion means that sRGB is a reasonably efficient use of the values in an integer-based image file to display human-discernible light levels. Unlike most other RGB color spaces, the sRGB gamma cannot be expressed as a numerical value. The overall gamma is approximately 2.2, consisting of a section near black, and a non-linear section elsewhere involving a 2.4 exponent. The purpose of the section is so the curve does not have an infinite slope at zero. The CIE XYZ values must be scaled so that the Y of D65 is 1.0 and this is usually true but some color spaces use 100 or other values. The first step in the calculation of sRGB from CIE XYZ is a linear transformation, = It is important to note that these linear RGB values are not the final result as they have not been adjusted for the gamma correction. SRGB was designed to reflect a typical real-world monitor with a gamma of 2.2, and the following formula transforms the linear RGB values into sRGB. If values in the range 0 to 255 are required, e. g. for video display or 8-bit graphics, the values are usually clipped to the 0 to 1 range. This clipping can be done before or after this gamma calculation, again the sRGB component values R s r g b, G s r g b, B s r g b are in the range 0 to 1. Followed by a multiplication of the linear values to get XYZ, = It is often casually stated that the decoding gamma for sRGB data is 2.2. The transformation was designed to approximate a gamma of about 2.2, but with a portion near zero to avoid having an infinite slope at K =0. The continuity condition for the curve C l i n e a r which is defined above as a function of C s r g b, is γ = K0 ϕ
3.
Red
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Red is the color at the longer-wavelengths end of the spectrum of visible light next to orange, at the opposite end from violet. Red color has a predominant light wavelength of roughly 620–740 nanometers, light with a longer wavelength than red but shorter than terahertz radiation and microwave is called infrared. Red is one of the secondary colors, resulting from the combination of yellow. Traditionally, it was viewed as a primary colour, along with yellow and blue, in the RYB color space and traditional color wheel formerly used by painters. Reds can vary in shade from light pink to very dark maroon or burgundy. Red is the color of cyan. In nature, the red color of blood comes from hemoglobin, the red color of the Grand Canyon and other geological features is caused by hematite or red ochre, both forms of iron oxide. It also causes the red color of the planet Mars, the color of autumn leaves is caused by pigments called anthocyanins, which are produced towards the end of summer, when the green chlorophyll is no longer produced. One to two percent of the population has red hair, the color is produced by high levels of the reddish pigment pheomelanin. Since red is the color of blood, it has historically been associated with sacrifice, danger, modern surveys in the United States and Europe show red is also the color most commonly associated with heat, activity, passion, sexuality, anger, love and joy. In China, India and many other Asian countries it is the color of symbolizing happiness, since the 19th century, red has also been associated with socialism and communism. The word red is derived from the Old English rēad, the word can be further traced to the Proto-Germanic rauthaz and the Proto-Indo European root rewdʰ-. In Sanskrit, the word means red or blood. In the Akkadian language of Ancient Mesopotamia and in the modern Inuit language of Inuit, the words for colored in Latin and Spanish both also mean red. In Portuguese the word for red is vermelho, which comes from Latin vermiculus, in the Russian language, the word for red, Кра́сный, comes from the same old Slavic root as the words for beautiful—красивый and excellent—прекрасный. Thus Red Square in Moscow, named long before the Russian Revolution, in heraldry, the word gules is used for red. Red can vary in hue from orange-red to violet-red, and for each hue there is a variety of shades and tints. Red hematite powder was found scattered around the remains at a grave site in a Zhoukoudian cave complex near Beijing
4.
Green
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Green is the color between blue and yellow on the spectrum of visible light. It is evoked by light with a predominant wavelength of roughly 495–570 nm, the modern English word green comes from the Middle English and Anglo-Saxon word grene, from the same Germanic root as the words grass and grow. It is the color of living grass and leaves and as a result is the color most associated with springtime, growth, by far the largest contributor to green in nature is chlorophyll, the chemical by which plants photosynthesize and convert sunlight into chemical energy. Many creatures have adapted to their environments by taking on a green hue themselves as camouflage. Several minerals have a color, including the emerald, which is colored green by its chromium content. In surveys made in Europe and the United States, green is the color most commonly associated with nature, life, health, youth, spring, hope and envy. In Europe and the U. S. green is associated with death, sickness, or the devil. In the Middle Ages and Renaissance, when the color of clothing showed the social status, green was worn by merchants, bankers. The Mona Lisa by Leonardo da Vinci wears green, showing she is not from a noble family, Green is also the traditional color of safety and permission, a green light means go ahead, a green card permits permanent residence in the United States. It is the most important color in Islam and it was the color of the banner of Muhammad, and is found in the flags of nearly all Islamic countries, and represents the lush vegetation of Paradise. It is also associated with the culture of Gaelic Ireland. Because of its association with nature, it is the color of the environmental movement, political groups advocating environmental protection and social justice describe themselves as part of the Green movement, some naming themselves Green parties. This has led to campaigns in advertising, as companies have sold green, or environmentally friendly. The word green comes from the Middle English and Old English word grene, which, like the German word grün, has the same root as the words grass and grow. It is from a Common Germanic *gronja-, which is reflected in Old Norse grænn, Old High German gruoni, ultimately from a PIE root *ghre- to grow. The first recorded use of the word as a term in Old English dates to ca. Latin with viridis also has a genuine and widely used term for green, related to virere to grow and ver spring, it gave rise to words in several Romance languages, French vert, Italian verde. Likewise the Slavic languages with zelenъ, Ancient Greek also had a term for yellowish, pale green – χλωρός, chloros, cognate with χλοερός verdant and χλόη the green of new growth
5.
Blue
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Blue is the colour between violet and green on the optical spectrum of visible light. Human eyes perceive blue when observing light with a wavelength between 450 and 495 nanometres, which is between 4500 and 4950 ångströms. Blues with a frequency and thus a shorter wavelength gradually look more violet, while those with a lower frequency. Pure blue, in the middle, has a wavelength of 470 nanometers, in painting and traditional colour theory, blue is one of the three primary colours of pigments, along with red and yellow, which can be mixed to form a wide gamut of colours. Red and blue mixed together form violet, blue and yellow together form green, Blue is also a primary colour in the RGB colour model, used to create all the colours on the screen of a television or computer monitor. The clear sky and the sea appear blue because of an optical effect known as Rayleigh scattering. When sunlight passes through the atmosphere, the wavelengths are scattered more widely by the oxygen and nitrogen molecules. An optical effect called Tyndall scattering, similar to Rayleigh scattering, explains blue eyes, distant objects appear more blue because of another optical effect called atmospheric perspective. Blue has been used for art and decoration since ancient times and it is the most important color in Judaism. In the Middle Ages, cobalt blue was used to colour the stained glass windows of cathedrals, beginning in the 9th century, Chinese artists used cobalt to make fine blue and white porcelain. Blue dyes for clothing were made from woad in Europe and indigo in Asia, in 1828 a synthetic ultramarine pigment was developed, and synthetic blue dyes and pigments gradually replaced mineral pigments and vegetable dyes. Pierre-Auguste Renoir, Vincent van Gogh and other late 19th century painters used ultramarine and cobalt blue not just to depict nature, in the late 18th century and 19th century, blue became a popular colour for military uniforms and police uniforms. In the 20th century, because blue was associated with harmony, it was chosen as the colour of the flags of the United Nations. Surveys in the US and Europe show that blue is the colour most commonly associated with harmony, faithfulness, confidence, distance, infinity, the imagination, cold, and sometimes with sadness. In US and European public opinion polls it is the most popular colour, Blue is the colour of light between violet and green on the visible spectrum. Blues also vary in shade or tint, darker shades of blue contain black or grey, darker shades of blue include ultramarine, cobalt blue, navy blue, and Prussian blue, while lighter tints include sky blue, azure, and Egyptian blue. Today most blue pigments and dyes are made by a chemical process, the modern English word blue comes from Middle English bleu or blewe, from the Old French bleu, a word of Germanic origin, related to the Old High German word blao. In heraldry, the azure is used for blue
6.
CMYK color model
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The CMYK color model is a subtractive color model, used in color printing, and is also used to describe the printing process itself. CMYK refers to the four used in some color printing, cyan, magenta, yellow. Though it varies by print house, press operator, press manufacturer, the K in CMYK stands for key because in four-color printing, cyan, magenta and yellow printing plates are carefully keyed, or aligned, with the key of the black key plate. Some sources suggest that the K in CMYK comes from the last letter in black and was chosen because B already means blue. Some sources claim this explanation, although useful as a mnemonic, is incorrect, the CMYK model works by partially or entirely masking colors on a lighter, usually white, background. The ink reduces the light that would otherwise be reflected, such a model is called subtractive because inks subtract brightness from white. In additive color models such as RGB, white is the combination of all primary colored lights. In the CMYK model, it is the opposite, white is the color of the paper or other background. To save cost on ink, and to produce deeper black tones, unsaturated and dark colors are produced by using black ink instead of the combination of cyan, magenta, with halftoning, a full continuous range of colors can be produced. To improve print quality and reduce moiré patterns, the screen for each color is set at a different angle. Common reasons for using black ink include, In traditional preparation of color separations, in some cases a black keyline was used when it served as both a color indicator and an outline to be printed in black. Because usually the black plate contained the keyline, the K in CMYK represents the keyline or black plate, also sometimes called the key plate. A combination of 100% cyan, magenta, and yellow inks soaks the paper with ink, making it slower to dry, causing bleeding, adding black ink absorbs more light and yields much better blacks. Using black ink is less expensive than using the corresponding amounts of colored inks. When a very dark area is desirable, a colored or gray CMY bedding is applied first, then a black layer is applied on top, making a rich, deep black. A black made with just CMY inks is sometimes called a composite black, the amount of black to use to replace amounts of the other ink is variable, and the choice depends on the technology, paper and ink in use. Processes called under color removal, under addition, and gray component replacement are used to decide on the final mix. CMYK or process color printing is contrasted with spot color printing, some printing presses are capable of printing with both four-color process inks and additional spot color inks at the same time
7.
Magenta
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Magenta is a color that is variously defined as purplish-red, reddish-purple, or mauvish-crimson. On computer screens, it is made by mixing equal amounts of blue, on color wheels of the RGB and CMY color models, it is located midway between red and blue. It is the color of green. It is one of the four colors of ink used in printing and by an inkjet printer, along with cyan, yellow. The tone of magenta used in printing is called printers magenta, Magenta was first introduced as the color of a new aniline dye called fuchsine, patented in 1859 by the French chemist François-Emmanuel Verguin. Its name was changed the year to magenta, to celebrate a victory of the French and Sardinian army at the Battle of Magenta on June 4,1859. The web color magenta is called fuchsia. Magenta is a color, meaning that it is not found in the visible spectrum of light. Rather, it is physiologically and psychologically perceived as the mixture of red and violet/blue light, with the absence of green. In the RGB color system, used to all the colors on a television or computer display, magenta is a secondary color, made by combining equal amounts of red. In this system, magenta is the color of green. In the CMYK color model, used in printing, it is one of the three primary colors, along with cyan and yellow, used to print all the rest of the colors. If magenta, cyan, and yellow are printed on top of each other on a page, in this model, magenta is the complementary color of green, and these two colors have the highest contrast and the greatest harmony. If combined, green and magenta ink will look dark gray or black, the magenta used in color printing, sometimes called process magenta, is a darker shade than the color used on computer screens. A purple hue in terms of theory, magenta is evoked by light having less power in green wavelengths than in blue/violet. In the Munsell color system, magenta is called red–purple, if the spectrum is wrapped to form a color wheel, magenta appears midway between red and violet. Violet and red, the two components of magenta, are at opposite ends of the spectrum and have very different wavelengths. The additive secondary color magenta, as noted above, is made by combining violet and red light at equal intensity, in optics, fuchsia and magenta are essentially the same color
8.
Yellow
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Yellow is the color between green and orange on the spectrum of visible light. It is evoked by light with a predominant wavelength of roughly 570–590 nm, in traditional color theory, used in painting, and in the subtractive color system, used in color printing, yellow is a primary color. In the RGB color model, used to create colors on television and computer screens, yellow is made by combining red, the word yellow comes from the Old English geolu, geolwe, meaning yellow, yellowish, derived from the Proto-Germanic word gelwaz yellow. It has the same Indo-European base, gʰel-, as the gold and yell. In Iran it has connotations of pallor/sickness, but also wisdom and it plays an important role in Asian culture, particularly in China, where it is seen as the color of happiness, glory, wisdom, harmony, and culture. The word yellow comes from the Old English geolu, geolwe, meaning yellow, yellowish and it has the same Indo-European base, gʰel-, as the words gold and yell, gʰel- means both bright and gleaming, and to cry out. The English term is related to other Germanic words for yellow, namely Scots yella, East Frisian jeel, West Frisian giel, Dutch geel, German gelb, and Swedish and Norwegian gul. According to the Oxford English Dictionary, the oldest known use of word in English is from The Epinal Glossary in 700. Yellow, in the form of yellow pigment made from clay, was one of the first colors used in prehistoric cave art. The cave of Lascaux has an image of a horse colored with yellow estimated to be 17,300 years old, in Ancient Egypt, yellow was associated with gold, which was considered to be imperishable, eternal and indestructible. The skin and bones of the gods were believed to be made of gold, the Egyptians used yellow extensively in tomb paintings, they usually used either yellow ochre or the brilliant orpiment, though it was made of arsenic and was highly toxic. A small paintbox with orpiment pigment was found in the tomb of King Tutankhamun, men were always shown with brown faces, women with yellow ochre or gold faces. The ancient Romans used yellow in their paintings to represent gold and it is found frequently in the murals of Pompeii. During the Post-Classical period, yellow became firmly established as the color of Judas Iscariot, from this connection, yellow also took on associations with envy, jealousy and duplicity. The tradition started in the Renaissance of marking non-Christian outsiders, such as Jews, in 16th century Spain, those accused of heresy and who refused to renounce their views were compelled to come before the Spanish Inquisition dressed in a yellow cape. The color yellow has been associated with moneylenders and finance. The National Pawnbrokers Associations logo depicts three golden spheres hanging from a bar, referencing the three bags of gold that the saint of pawnbroking, St. Nicholas, holds in his hands. Additionally, the symbol of three golden orbs is found in the coat of arms of the House of Medici, a fifteenth century Italian dynasty of bankers and lenders
9.
Black
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Black is the darkest color resulting from the absence or complete absorption of light. Like white and grey, it is a color, literally a color without hue. It is one of the four colors in the CMYK color model, along with cyan, yellow. Black is often used to represent darkness, it is the symbolic opposite of white, Black was one of the first colors used by artists in neolithic cave paintings. In the 14th century, it began to be worn by royalty and it became the color worn by English romantic poets, businessmen and statesmen in the 19th century, and a high fashion color in the 20th century. In the Roman Empire, it became the color of mourning, according to surveys in Europe and North America, it is the color most commonly associated with mourning, the end, secrets, magic, force, violence, evil, and elegance. More distant cognates include Latin flagrare, and Ancient Greek phlegein, the Ancient Greeks sometimes used the same word to name different colors, if they had the same intensity. Kuanos could mean both dark blue and black, the Ancient Romans had two words for black, ater was a flat, dull black, while niger was a brilliant, saturated black. Ater has vanished from the vocabulary, but niger was the source of the country name Nigeria the English word Negro, old High German also had two words for black, swartz for dull black and blach for a luminous black. These are parallelled in Middle English by the terms swart for dull black, swart still survives as the word swarthy, while blaek became the modern English black. In heraldry, the used for the black color is sable, named for the black fur of the sable. Black was one of the first colors used in art, the Lascaux Cave in France contains drawings of bulls and other animals drawn by paleolithic artists between 18,000 and 17,000 years ago. They began by using charcoal, and then made more vivid black pigments by burning bones or grinding a powder of manganese oxide, for the ancient Egyptians, black had positive associations, being the color of fertility and the rich black soil flooded by the Nile. It was the color of Anubis, the god of the underworld, who took the form of a black jackal, and offered protection against evil to the dead. For the ancient Greeks, black was also the color of the underworld, separated from the world of the living by the river Acheron and those who had committed the worst sins were sent to Tartarus, the deepest and darkest level. In the center was the palace of Hades, the king of the underworld, Black was one of the most important colors used by ancient Greek artists. In the 6th century BC, they began making pottery and later red figure pottery. In black-figure pottery, the artist would paint figures with a clay slip on a red clay pot
10.
HSL and HSV
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HSL and HSV are the two most common cylindrical-coordinate representations of points in an RGB color model. The two representations rearrange the geometry of RGB in an attempt to be intuitive and perceptually relevant than the cartesian representation. Developed in the 1970s for computer applications, HSL and HSV are used today in color pickers, in image editing software. HSL stands for hue, saturation, and lightness, and is often called HLS. HSV stands for hue, saturation, and value, and is often called HSB. A third model, common in computer applications, is HSI. However, while typically consistent, these definitions are not standardized, note that while hue in HSL and HSV refers to the same attribute, their definitions of saturation differ dramatically. As a result, each unique RGB device has unique HSL and HSV absolute color spaces to accompany it, other more computationally intensive models, such as CIELAB or CIECAM02, are said to better achieve these goals. In each geometry, the 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. These saturated colors have lightness ½ in HSL, while in HSV they have value 1, mixing these pure colors with black—producing so-called shades—leaves saturation unchanged. In HSL, saturation is also unchanged by tinting with white, in HSV, tinting alone reduces saturation. Confusingly, such diagrams usually label this radial dimension saturation, blurring or erasing the distinction between saturation and chroma, as described below, computing chroma is a helpful step in the derivation of each model. Most televisions, computer displays, and projectors produce colors by combining red, green, furthermore, neither additive nor subtractive color models define color relationships the same way the human eye does. For example, imagine we have an RGB display whose color is controlled by three sliders ranging from 0–255, one controlling the intensity of each of the red, green, consequently, these models and similar ones have become ubiquitous throughout image editing and graphics software since then. Some of their uses are described below, nonetheless, it is worth reviewing those definitions before leaping into the derivation of our models. Hue The attribute of a visual sensation according to which an area appears to be similar to one of the colors, red, yellow, green. Radiance The radiant power of passing through a particular surface per unit solid angle per unit projected area. Luminance The radiance weighted by the effect of each wavelength on a human observer
11.
Hue
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Orange and violet are the other hues, for a total of six, as in the rainbow, red, orange, yellow, green, blue, violet. The other color appearance parameters are colorfulness, chroma, saturation, lightness, usually, colors with the same hue are distinguished with adjectives referring to their lightness and/or colorfulness, such as with light blue, pastel blue, vivid blue. Exceptions include brown, which is a dark orange, in painting color theory, a hue refers to a pure color—one without tint or shade. A hue is an element of the color wheel, hues are first processed in the brain in areas in the extended V4 called globs. Hue is the component of the polar representation, while chroma is the radial component. Specifically, in CIELAB h a b = a t a n 2, while, analogously, in CIELUV h u v = a t a n 2 = a t a n 2, where, atan2 is a two-argument inverse tangent. Preucil describes a color hexagon, similar to a trilinear plot described by Evans, Hanson, and Brewer, to place red at 0°, green at 120°, and blue at 240°, h r g b = a t a n 2. Equivalently, one may solve tan =3 ⋅2 ⋅ R − G − B, Preucil used a polar plot, which he termed a color circle. Using R, G, and B, one may compute hue angle using the scheme, determine which of the six possible orderings of R, G. Note that in case the formula contains the fraction M − L H − L, where H is the highest of R, G, and B, L is the lowest. This is referred to as the Preucil hue error and was used in the computation of mask strength in photomechanical color reproduction, the formulae used are those in the table above. The hues exhibited by caramel colorings and beers are fairly limited in range, the Linner hue index is used to quantify the hue of such products. Replacements are often used for chromium, cadmium and alizarin, dominant wavelength is a physical analog to the perceptual attribute hue. On a chromaticity diagram, a line is drawn from a point through the coordinates of the color in question. There are two ways in which hue difference is quantified. The first is the difference between the two hue angles. The symbol for expression of hue difference is Δ h a b in CIELAB. The other is computed as the total color difference after Lightness and Chroma differences have been accounted for, its symbol is Δ H a b ∗ in CIELAB
12.
Colorfulness
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Colorfulness or saturation in colorimetry and color theory refers to the perceived intensity of a specific color. Colorfulness is the visual sensation according to which the color of an area appears to be more or less chromatic. Chroma is the relative to the brightness of a similarly illuminated area that appears to be white or highly transmitting. Therefore, chroma should not be confused with colorfulness, saturation is the colorfulness of a color relative to its own brightness. A highly colorful stimulus is vivid and intense, while a less colorful stimulus appears more muted, with no colorfulness at all, a color is a “neutral” gray. Any color can be described using three color appearance parameters — colorfulness, lightness, and hue, saturation is one of three coordinates in the HSL and HSV color spaces. The saturation of a color is determined by a combination of light intensity, the purest color is achieved by using just one wavelength at a high intensity, such as in laser light. If the intensity drops, then as a result the saturation drops, to desaturate a color of given intensity in a subtractive system, one can add white, black, gray, or the hues complement. CIELUV The chroma normalized by the lightness, s u v = C u v ∗ L ∗ =132 +2 where is the chromaticity of the white point, and chroma is defined below. Nevertheless, this provides a reasonable predictor of saturation. S a b = C a b ∗ C a b ∗2 + L ∗2100 % where Sab is the saturation, L* the lightness and C*ab is the chroma of the color. CIECAM02 The square root of the colorfulness divided by the brightness, M is proportional to the chroma C, thus the CIECAM02 definition bears some similarity to the CIELUV definition. An important difference is that the CIECAM02 model accounts for the conditions through the parameter FL. Different color spaces, such as CIELAB or CIELUV may be used, the naïve definition of saturation does not specify its response function. However, both color spaces are nonlinear in terms of perceived color differences. It is also possible—and sometimes desirable—to define a quantity that is linearized in term of the psychovisual perception. The transformation of to is given by, C a b ∗ = a ∗2 + b ∗2 h a b = arctan b ∗ a ∗ and analogously for CIE L*C*h. The chroma in the CIE L*C*h and CIE L*C*h coordinates has the advantage of being more psychovisually linear, and therefore, chroma in CIE1976 L*a*b* and L*u*v* color spaces is very much different from the traditional sense of saturation
13.
Brightness
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Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. In other words, brightness is the perception elicited by the luminance of a visual target and it is not necessarily proportional to luminance. This is a subjective attribute/property of an object being observed and one of the color appearance parameters of color appearance models, brightness refers to an absolute term and should not be confused with Lightness. The adjective bright derives from an Old English beorht with the same meaning via metathesis giving Middle English briht, the word is from a Common Germanic *berhtaz, ultimately from a PIE root with a closely related meaning, *bhereg- white, bright. Brightness was formerly used as a synonym for the term luminance. As defined by the US Federal Glossary of Telecommunication Terms, brightness should now be used only for non-quantitative references to physiological sensations and perceptions of light, a given target luminance can elicit different perceptions of brightness in different contexts, see, for example, Whites illusion. With regard to stars, brightness is quantified as apparent magnitude, brightness is, at least in some respects, the antonym of darkness. The United States Federal Trade Commission has assigned a meaning to brightness when applied to lamps. When appearing on light bulb packages, brightness means Luminous flux, Luminous flux is the total amount of light coming from a source, such as a lighting device. Luminance, the meaning of brightness, is the amount of light per solid angle coming from an area. The table below shows the ways of indicating the amount of light. The term brightness is used in discussions of sound timbres. Luma Luminance Luminosity Media related to brightness at Wikimedia Commons Poyntons Color FAQ
14.
Tints and shades
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In color theory, a tint is the mixture of a color with white, which increases lightness, and a shade is the mixture of a color with black, which reduces lightness. A tone is produced either by the mixture of a color with gray, mixing a color with any neutral color reduces the chroma, or colorfulness, while the hue remains unchanged. When mixing colored light, the mixture of spectrally balanced red, green and blue is always white. When we mix colorants, such as the pigments in paint mixtures and this moves the mixed color toward a neutral color—a gray or near-black. Lights are made brighter or dimmer by adjusting their brightness, or energy level, in painting, lightness is adjusted through mixture with white, black or a colors complement. It is common among some painters to darken a paint color by adding black paint—producing colors called shades—or to lighten a color by adding white—producing colors called tints. However, this is not always the best way for representational painting, for instance, darkening a color by adding black can cause colors such as yellows, reds and oranges, to shift toward the greenish or bluish part of the spectrum. Lightening a color by adding white can cause a shift towards blue when mixed with reds and oranges. When lightening a color this hue shift can be corrected with the addition of an amount of an adjacent color to bring the hue of the mixture back in line with the parent color
15.
Primary color
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A set of primary colors is a small, arbitrary set of pigmented physical media, lights or purely abstract elements of a mathematical colorspace model. Distinct colors from a larger gamut can be specified in terms of a mixture of colors which facilitates technological applications such as painting, electronic displays. Any small set of pigments or lights are imperfect physical primary colors in that they cannot be mixed to yield all possible colors that can be perceived by the color vision system. In an additive set of colors, as in coincident projected lights or in electronic visual displays, in a subtractive set of colors, as in mixing of pigments or dyes for printing, the colors magenta, yellow and cyan are normally used. See RGB color model, and CMYK color model for more on these sets of primary colors. Primary colors are not a property of light but are related to the color vision system in animals. The human eye normally contains three types of color photoreceptors that are associated with specialized cone cells. Each photoreceptor responds to different ranges of the electromagnetic spectrum. Humans and other species with three types of color photoreceptor are known as trichromats. Color appearance models like CIECAM02 describe color more generally in six dimensions, most placental mammals other than primates have only two types of color photoreceptor and are therefore dichromats while birds and marsupials are tetrachromats with four color photoreceptor types. There is no peer reviewed scholarly work that has confirmed the existence of a functional human tetrachromat though they are suspected to exist. Demonstrating improved spectral discrimination in any animal can be difficult since complex sets of neurons affect color perception in ways that are difficult to interrogate. Before the nature of colorimetry and visual physiology were well understood a number of color models assigned primary colors to different hues. Young originally proposed red, green and violet, and Maxwell changed violet to blue, Helmholtz proposed a slightly red, a vegetation-green, slightly yellowish. In modern understanding, human cells do not correspond precisely to a specific set of primary colors. There are hundreds of available pigments for visual artists to use. A common approach is to use just a palette of pigments that can be physically mixed to any color that the artist desires in the final work. Contemporary classical realists have often advocated that a palette of white, red, yellow
16.
Color
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Color or colour is the characteristic of human visual perception described through color categories, with names such as red, yellow, purple, or blue. This perception of color derives from the stimulation of cells in the human eye by electromagnetic radiation in the spectrum of light. Color categories and physical specifications of color are associated with objects through the wavelength of the light that is reflected from them and this reflection is governed by the objects physical properties such as light absorption, emission spectra, etc. By defining a color space, colors can be identified numerically by coordinates, there may also be more than three color dimensions in other color spaces, such as in the CMYK color model, wherein one of the dimensions relates to a colours colorfulness). The photo-receptivity of the eyes of species also varies considerably from our own. Honeybees and bumblebees for instance have trichromatic color vision sensitive to ultraviolet but is insensitive to red, papilio butterflies possess six types of photoreceptors and may have pentachromatic vision. The most complex color vision system in the kingdom has been found in stomatopods with up to 12 spectral receptor types thought to work as multiple dichromatic units. The science of color is sometimes called chromatics, colorimetry, or simply color science and it includes the perception of color by the human eye and brain, the origin of color in materials, color theory in art, and the physics of electromagnetic radiation in the visible range. Electromagnetic radiation is characterized by its wavelength and its intensity, when the wavelength is within the visible spectrum, it is known as visible light. Most light sources emit light at different wavelengths, a sources spectrum is a distribution giving its intensity at each wavelength. Although the spectrum of light arriving at the eye from a given direction determines the color sensation in that direction, in each such class the members are called metamers of the color in question. The table at right shows approximate frequencies and wavelengths for various pure spectral colors, the wavelengths listed are as measured in air or vacuum. A common list identifies six main bands, red, orange, yellow, green, blue, Newtons conception included a seventh color, indigo, between blue and violet. It is possible that what Newton referred to as blue is nearer to what today is known as cyan, the color of an object depends on both the physics of the object in its environment and the characteristics of the perceiving eye and brain. Some objects not only light, but also transmit light or emit light themselves. This effect is known as color constancy, opaque objects that do not reflect specularly have their color determined by which wavelengths of light they scatter strongly. If objects scatter all wavelengths with roughly equal strength, they appear white, if they absorb all wavelengths, they appear black. Opaque objects that reflect light of different wavelengths with different efficiencies look like mirrors tinted with colors determined by those differences
17.
Subtractive primary
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A set of primary colors is a small, arbitrary set of pigmented physical media, lights or purely abstract elements of a mathematical colorspace model. Distinct colors from a larger gamut can be specified in terms of a mixture of colors which facilitates technological applications such as painting, electronic displays. Any small set of pigments or lights are imperfect physical primary colors in that they cannot be mixed to yield all possible colors that can be perceived by the color vision system. In an additive set of colors, as in coincident projected lights or in electronic visual displays, in a subtractive set of colors, as in mixing of pigments or dyes for printing, the colors magenta, yellow and cyan are normally used. See RGB color model, and CMYK color model for more on these sets of primary colors. Primary colors are not a property of light but are related to the color vision system in animals. The human eye normally contains three types of color photoreceptors that are associated with specialized cone cells. Each photoreceptor responds to different ranges of the electromagnetic spectrum. Humans and other species with three types of color photoreceptor are known as trichromats. Color appearance models like CIECAM02 describe color more generally in six dimensions, most placental mammals other than primates have only two types of color photoreceptor and are therefore dichromats while birds and marsupials are tetrachromats with four color photoreceptor types. There is no peer reviewed scholarly work that has confirmed the existence of a functional human tetrachromat though they are suspected to exist. Demonstrating improved spectral discrimination in any animal can be difficult since complex sets of neurons affect color perception in ways that are difficult to interrogate. Before the nature of colorimetry and visual physiology were well understood a number of color models assigned primary colors to different hues. Young originally proposed red, green and violet, and Maxwell changed violet to blue, Helmholtz proposed a slightly red, a vegetation-green, slightly yellowish. In modern understanding, human cells do not correspond precisely to a specific set of primary colors. There are hundreds of available pigments for visual artists to use. A common approach is to use just a palette of pigments that can be physically mixed to any color that the artist desires in the final work. Contemporary classical realists have often advocated that a palette of white, red, yellow
18.
Printing
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Printing is a process for reproducing text and images using a master form or template. The earliest examples include Cylinder seals and other such as the Cyrus Cylinder. The earliest known form of printing came from China dating to before 220 A. D. Later developments in printing include the type, first developed by Bi Sheng in China around 1040 AD. Johannes Gutenberg introduced mechanical movable type printing to Europe in the 15th century, modern large-scale printing is typically done using a printing press, while small-scale printing is done free-form with a digital printer. Though paper is the most common material, it is frequently done on metals, plastics, cloth. On paper it is carried out as a large-scale industrial process and is an essential part of publishing. Woodblock printing is a technique for printing text, images or patterns that was used widely throughout East Asia and it originated in China in antiquity as a method of printing on textiles and later on paper. As a method of printing on cloth, the earliest surviving examples from China date to before 220 A. D, the earliest surviving woodblock printed fragments are from China. They are of silk printed with flowers in three colours from the Han Dynasty and they are the earliest example of woodblock printing on paper appeared in the mid-seventh century in China. By the ninth century, printing on paper had taken off, by the tenth century,400,000 copies of some sutras and pictures were printed, and the Confucian classics were in print. A skilled printer could print up to 2,000 double-page sheets per day, Printing spread early to Korea and Japan, which also used Chinese logograms, but the technique was also used in Turpan and Vietnam using a number of other scripts. This technique then spread to Persia and Russia and this technique was transmitted to Europe via the Islamic world, and by around 1400 was being used on paper for old master prints and playing cards. However, Arabs never used this to print the Quran because of the limits imposed by Islamic doctrine, block printing, called tarsh in Arabic developed in Arabic Egypt during the ninth-tenth centuries, mostly for prayers and amulets. There is some evidence to suggest that these print blocks made from non-wood materials, possibly tin, lead, the techniques employed are uncertain, however, and they appear to have had very little influence outside of the Muslim world. Though Europe adopted woodblock printing from the Muslim world, initially for fabric, block printing later went out of use in Islamic Central Asia after movable type printing was introduced from China. Block printing first came to Europe as a method for printing on cloth, images printed on cloth for religious purposes could be quite large and elaborate. When paper became relatively easily available, around 1400, the medium transferred very quickly to small religious images
19.
Color printing
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Color printing or colour printing is the reproduction of an image or text in color. The additive combination of any two colors in roughly equal proportion gives rise to the perception of a secondary color. For example, red and green yields yellow, red and blue yields magenta, yellow, cyan and magenta are merely the basic secondary colors, unequal mixtures of the primaries give rise to perception of many other colors all of which may be considered tertiary. While there are techniques for reproducing images in color, specific graphic processes. In this type of industrial or commercial printing, the used to print full-color images. Four inks are used, three colors plus black. These ink colors are cyan, magenta, yellow and key, cyan can be thought of as minus-red, magenta as minus-green, and yellow as minus-blue. These inks are semi-transparent or translucent, where two such inks overlap on the paper due to sequential printing impressions, a primary color is perceived. For example, yellow overprinted by magenta yields red, the secondary or subtractive colors cyan, magenta and yellow may be considered primary by printers and watercolorists. Two graphic techniques are required to prepare images for four-color printing, in the pre-press stage, original images are translated into forms that can be used on a printing press, through color separation, and screening or halftoning. These steps make possible the creation of printing plates that can transfer color impressions to paper on printing presses based on the principles of lithography. An emerging method of printing is six-color process printing which adds orange and green to the traditional CMYK inks for a larger and more vibrant gamut. However, such alternate color systems still rely on color separation, halftoning, color printing can also involve as few as one color ink, or multiple color inks which are not the primary colors. Using a limited number of inks, or specific color inks in addition to the primary colors, is referred to as spot color printing. Generally, spot-color inks are specific formulations that are designed to print alone, the range of available spot color inks, much like paint, is nearly unlimited, and much more varied than the colors that can be produced by four-color-process printing. Spot-color inks range from pastels to intense fluorescents to reflective metallics. Color printing involves a series of steps, or transformations, to generate a quality color reproduction, the following sections focus on the steps used when reproducing a color image in CMYK printing, along with some historical perspective. Woodblock printing on textiles preceded printing on paper in both Asia and Europe, and the use of different blocks to produce patterns in color was common
20.
Comic strip
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A comic strip is a sequence of drawings arranged in interrelated panels to display brief humor or form a narrative, often serialized, with text in balloons and captions. With the development of the internet, they began to online as web comics. There were more than 200 different comic strips and daily cartoon panels in American newspapers alone each day for most of the 20th century, Strips are written and drawn by a comics artist or cartoonist. As the name implies, comic strips can be humorous, starting in the late 1920s, comic strips expanded from their mirthful origins to feature adventure stories, as seen in Popeye, Captain Easy, Buck Rogers, Tarzan, and The Adventures of Tintin. Soap-opera continuity strips such as Judge Parker and Mary Worth gained popularity in the 1940s, all are called, generically, comic strips, though cartoonist Will Eisner has suggested that sequential art would be a better genre-neutral name. In the UK and the rest of Europe, comic strips are also serialized in comic book magazines, storytelling using a sequence of pictures has existed through history. One medieval European example in textile form is the Bayeux Tapestry, printed examples emerged in 19th-century Germany and in 18th-century England, where some of the first satirical or humorous sequential narrative drawings were produced. William Hogarths 18th century English cartoons include both narrative sequences, such as A Rakes Progress, and single panels, in China, with its traditions of block printing and of the incorporation of text with image, experiments with what became lianhuanhua date back to 1884. The first newspaper comic strips appeared in North America in the late 19th century, the Yellow Kid is usually credited as one of the first newspaper strips. However, the art form combining words and pictures developed gradually, swiss author and caricature artist Rodolphe Töpffer is considered the father of the modern comic strips. In 1865, German painter, author, and caricaturist Wilhelm Busch created the strip Max and Moritz, Max and Moritz provided an inspiration for German immigrant Rudolph Dirks, who created the Katzenjammer Kids in 1897. Familiar comic-strip iconography such as stars for pain, sawing logs for snoring, speech balloons, hugely popular, Katzenjammer Kids occasioned one of the first comic-strip copyright ownership suits in the history of the medium. When Dirks left William Randolph Hearst for the promise of a better salary under Joseph Pulitzer, it was an unusual move, in a highly unusual court decision, Hearst retained the rights to the name Katzenjammer Kids, while creator Dirks retained the rights to the characters. Hearst promptly hired Harold Knerr to draw his own version of the strip, Dirks renamed his version Hans and Fritz. Thus, two versions distributed by rival syndicates graced the pages for decades. Dirks version, eventually distributed by United Feature Syndicate, ran until 1979, in the United States, the great popularity of comics sprang from the newspaper war between Pulitzer and Hearst. On January 31,1912, Hearst introduced the nations first full daily comic page in his New York Evening Journal, the history of this newspaper rivalry and the rapid appearance of comic strips in most major American newspapers is discussed by Ian Gordon. The longest running American comic strips are,1, barney Google and Snuffy Smith 5
21.
RGB color model
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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 primary colors, red, green and blue. Before the electronic age, the RGB color model already had a theory behind it. 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, video games, and digital cameras. Typical RGB output devices are TV sets of technologies, computer and mobile phone displays, video projectors, multicolor LED displays. Color printers, on the hand are not RGB devices. This article discusses concepts common to all the different color spaces that use the RGB color model, to form a color with RGB, three light beams must be superimposed. Each of the three beams is called a component of color, and each of them can have an arbitrary intensity, from fully off to fully on. The RGB color model is additive in the sense that the three beams are added together, and their light spectra add, wavelength for wavelength. This is essentially opposite to the color model that applies to paints, inks, dyes. 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, the result is a colorized hue, a secondary color is formed by the sum of two primary colors of equal intensity, cyan is green+blue, magenta is red+blue, and yellow is red+green. 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 absolute, but relative to the primary colors. When the exact chromaticities of the red, green and blue primaries are defined, the normal three kinds of light-sensitive photoreceptor cells in the human eye respond most to yellow, green, and violet light. As an example, suppose that light in the range of wavelengths enters the eye. 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 this difference is the basis of our perception of orange. Thus, the appearance of an object results from light from the object entering our eye and stimulating the different cones simultaneously. The first experiments with RGB in early color photography were made in 1861 by Maxwell himself, to reproduce the color photograph, three matching projections over a screen in a dark room were necessary
22.
Light
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Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to light, which is visible to the human eye and is responsible for the sense of sight. Visible light is defined as having wavelengths in the range of 400–700 nanometres, or 4.00 × 10−7 to 7.00 × 10−7 m. This wavelength means a range of roughly 430–750 terahertz. The main source of light on Earth is the Sun, sunlight provides the energy that green plants use to create sugars mostly in the form of starches, which release energy into the living things that digest them. This process of photosynthesis provides virtually all the used by living things. Historically, another important source of light for humans has been fire, with the development of electric lights and power systems, electric lighting has effectively replaced firelight. Some species of animals generate their own light, a process called bioluminescence, for example, fireflies use light to locate mates, and vampire squids use it to hide themselves from prey. Visible light, as all types of electromagnetic radiation, is experimentally found to always move at this speed in a vacuum. In physics, the term sometimes refers to electromagnetic radiation of any wavelength. In this sense, gamma rays, X-rays, microwaves and radio waves are also light, like all types of light, visible light is emitted and absorbed in tiny packets called photons and exhibits properties of both waves and particles. This property is referred to as the wave–particle duality, the study of light, known as optics, is an important research area in modern physics. Generally, EM radiation, or EMR, is classified by wavelength into radio, microwave, infrared, the behavior of EMR depends on its wavelength. Higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths, when EMR interacts with single atoms and molecules, its behavior depends on the amount of energy per quantum it carries. There exist animals that are sensitive to various types of infrared, infrared sensing in snakes depends on a kind of natural thermal imaging, in which tiny packets of cellular water are raised in temperature by the infrared radiation. EMR in this range causes molecular vibration and heating effects, which is how these animals detect it, above the range of visible light, ultraviolet light becomes invisible to humans, mostly because it is absorbed by the cornea below 360 nanometers and the internal lens below 400. Furthermore, the rods and cones located in the retina of the eye cannot detect the very short ultraviolet wavelengths and are in fact damaged by ultraviolet. Many animals with eyes that do not require lenses are able to detect ultraviolet, by quantum photon-absorption mechanisms, various sources define visible light as narrowly as 420 to 680 to as broadly as 380 to 800 nm
23.
Additive primary
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A set of primary colors is a small, arbitrary set of pigmented physical media, lights or purely abstract elements of a mathematical colorspace model. Distinct colors from a larger gamut can be specified in terms of a mixture of colors which facilitates technological applications such as painting, electronic displays. Any small set of pigments or lights are imperfect physical primary colors in that they cannot be mixed to yield all possible colors that can be perceived by the color vision system. In an additive set of colors, as in coincident projected lights or in electronic visual displays, in a subtractive set of colors, as in mixing of pigments or dyes for printing, the colors magenta, yellow and cyan are normally used. See RGB color model, and CMYK color model for more on these sets of primary colors. Primary colors are not a property of light but are related to the color vision system in animals. The human eye normally contains three types of color photoreceptors that are associated with specialized cone cells. Each photoreceptor responds to different ranges of the electromagnetic spectrum. Humans and other species with three types of color photoreceptor are known as trichromats. Color appearance models like CIECAM02 describe color more generally in six dimensions, most placental mammals other than primates have only two types of color photoreceptor and are therefore dichromats while birds and marsupials are tetrachromats with four color photoreceptor types. There is no peer reviewed scholarly work that has confirmed the existence of a functional human tetrachromat though they are suspected to exist. Demonstrating improved spectral discrimination in any animal can be difficult since complex sets of neurons affect color perception in ways that are difficult to interrogate. Before the nature of colorimetry and visual physiology were well understood a number of color models assigned primary colors to different hues. Young originally proposed red, green and violet, and Maxwell changed violet to blue, Helmholtz proposed a slightly red, a vegetation-green, slightly yellowish. In modern understanding, human cells do not correspond precisely to a specific set of primary colors. There are hundreds of available pigments for visual artists to use. A common approach is to use just a palette of pigments that can be physically mixed to any color that the artist desires in the final work. Contemporary classical realists have often advocated that a palette of white, red, yellow
24.
Air Force blue
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Air Force blue colours are a variety of colours that are mostly various tones of the colour azure, the purest tones of which are identified as being the colour of the sky on a clear day. However, they are actually dark tones of azure, not blue and these air force blue colours are used by these various air forces for colour identification. Air Force blue, more specifically Air Force blue or RAF blue, is a shade of the colour azure. Similar shades are used in Royal Air Force uniforms and the Royal Air Force Ensign. The field of the RAF ensign is specified as NATO stock no. 8305-99-130-4578, the shade of the colour that is shown in the colour info-box is the shade of air force blue used by the Royal Air Force. e. The Royal Canadian Air Force, the Royal Australian Air Force, displayed at right is the colour Air Force blue. US Air Force blue is designated as the colour Pantone 287, displayed at right is the colour US Air Force Academy blue. The US Air Force Academy uses a particular shade of azure, subtly different from US Air Force blue, in its sporting and other insignia, displayed at right is the web colour sky blue. The first recorded use of sky blue as a name in English was in 1728 in the Cyclopædia of Ephraim Chambers. Displayed at right is the colour aero, the first recorded use of aero as a colour name in English was in 1920. Displayed at right is the wild blue yonder. This Crayola colour was formulated in 2003, apparently, it represents the colour of the sky on a cloudy, stormy day. At right is displayed the colour air superiority blue/PRU Blue, the source of this colour is Federal Standard 595, a U. S. Federal Government standard set up in 1956 for paint colours which is mostly used by military contractors and also in engineering. Air superiority blue is designated as Federal Standard 595 colour #FS15450, photographic Reconnaissance Unit Blue was devised by the RAF during WW II as a low visibility camouflage colour for its high-flying Spitfire and Mosquito reconnaissance aircraft. As air superiority blue it was adopted by the US Army Air Force and was added as one of the colours when the Federal Standard 595 colour list was set up in 1956. This colour is used as camouflage by being painted on the sides of reconnaissance aircraft to make them less visible from the ground. The colour blue yonder is displayed at right, the source of this colour is the Pantone Textile Paper eXtended colour list, colour #18-3937 TPX—Blue Yonder
25.
Sharpie (marker)
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Sharpie is a brand of writing instruments manufactured by Newell Brands, a public company, headquartered in Hoboken, NJ. Sharpie markers are made with a number of tips, the most common and popular is the Fine tip. Other tips include Ultra Fine Point, Extra Fine Point, Brush tip, Chisel tip, Sharpie was originally a name designating a permanent marker launched in 1964 by the Sanford Ink Company. The Sharpie also became the first pen-style permanent marker, in 1990 Sharpie was acquired by The Newell Companies as part of Sanford, a leading manufacturer and marketer of writing instruments. In 2005, the companys popular Accent highlighter brand was repositioned under the Sharpie brand name, a new version of Sharpie called Sharpie Mini was launched, which are markers half the size of a normal Sharpie and feature a clip to attach the Sharpie to a keychain or lanyard. In 2006, Sharpie released a new line of markers that had a button activated retractable tip rather than a cap, Sharpie Paint markers were also introduced. As of 2002,200 million Sharpies had been sold worldwide, Sharpie markers are manufactured in Mexicali, Baja California, Mexico and Maryville, TN, and with numerous off-shore partners globally. Sharpie sponsored the NASCAR Sprint Cup Series Sharpie 500, a popular night-time race at Bristol Motor Speedway, for the 2010 season, Newell Rubbermaid switched the sponsorship for this race to its Irwin Tools brand. Sharpie sponsored the Nationwide Series Sharpie Mini 300 race from 2004 to 2008, prior to 2006, they sponsored Kurt Busch, who was the 2004 Sprint Cup champion. Sharpie also sponsored Jamie McMurray in the 2006 NASCAR Sprint Cup Series, in recent years, Sharpie commercials have followed the slogan Write Out Loud. Also, an aged woman trying to think of what to write for her resignation letter. David Beckham is sponsored by Sharpie and appears in a commercial signing autographs with a Sharpie, though Sharpie ink will become mostly permanent after setting, it can be erased. A dry erase marker is usually successful in removing sharpie ink by covering the sharpie ink using three to four pen strokes, wD-40 will work moderately well on recent markings if dry-erase markers are not available. Crayolas Color Wonder mess-free markers have also been effective in removing Sharpie ink that has dried for several days. Isopropyl alcohol works well and is damaging to some surfaces, rubbing alcohol is the dilute form. On some surfaces, the ink can be removed by coloring over the ink with a dry erase marker and then removing the Sharpie ink, steam cleaning has proved effective, as have rubber erasers. Magic Eraser has also proven somewhat effective on hard surfaces such as brick, there are no warning labels on Sharpie markers. They bear the new AP certification symbol of The Art & Creative Materials Institute, however, this does not mean that materials are not irritants or allergens
26.
Fluorescence
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Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence, in most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation. Fluorescent materials cease to glow immediately when the radiation source stops, unlike phosphorescence, Fluorescence also occurs frequently in nature in some minerals and in various biological states in many branches of the animal kingdom. An early observation of fluorescence was described in 1560 by Bernardino de Sahagún and it was derived from the wood of two tree species, Pterocarpus indicus and Eysenhardtia polystachya. The chemical compound responsible for this fluorescence is matlaline, which is the product of one of the flavonoids found in this wood. The name was derived from the fluorite, some examples of which contain traces of divalent europium. In a key experiment he used a prism to isolate ultraviolet radiation from sunlight, the specific frequencies of exciting and emitted light are dependent on the particular system. S0 is called the state of the fluorophore, and S1 is its first excited singlet state. A molecule in S1 can relax by various competing pathways and it can undergo non-radiative relaxation in which the excitation energy is dissipated as heat to the solvent. Excited organic molecules can also relax via conversion to a triplet state, relaxation from S1 can also occur through interaction with a second molecule through fluorescence quenching. Molecular oxygen is an extremely efficient quencher of fluorescence just because of its unusual triplet ground state, in most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation, this phenomenon is known as the Stokes shift. The emitted radiation may also be of the wavelength as the absorbed radiation. Molecules that are excited through light absorption or via a different process can transfer energy to a second sensitized molecule, the fluorescence quantum yield gives the efficiency of the fluorescence process. It is defined as the ratio of the number of photons emitted to the number of photons absorbed, Φ = Number of photons emitted Number of photons absorbed The maximum fluorescence quantum yield is 1.0, each photon absorbed results in a photon emitted. Compounds with quantum yields of 0.10 are still considered quite fluorescent, thus, if the rate of any pathway changes, both the excited state lifetime and the fluorescence quantum yield will be affected. Fluorescence quantum yields are measured by comparison to a standard, the quinine salt quinine sulfate in a sulfuric acid solution is a common fluorescence standard. The fluorescence lifetime refers to the time the molecule stays in its excited state before emitting a photon. This is an instance of exponential decay, various radiative and non-radiative processes can de-populate the excited state
Color coordinates
