1.
Algeria
–
Algeria, officially the Peoples Democratic Republic of Algeria, is a sovereign state in North Africa on the Mediterranean coast. Its capital and most populous city is Algiers, located in the far north. With an area of 2,381,741 square kilometres, Algeria is the tenth-largest country in the world, the country is a semi-presidential republic consisting of 48 provinces and 1,541 communes. Abdelaziz Bouteflika has been President since 1999, Berbers are the indigenous inhabitants of Algeria. Algeria is a regional and middle power, the North African country supplies large amounts of natural gas to Europe, and energy exports are the backbone of the economy. According to OPEC Algeria has the 16th largest oil reserves in the world, Sonatrach, the national oil company, is the largest company in Africa. Algeria has one of the largest militaries in Africa and the largest defence budget on the continent, most of Algerias weapons are imported from Russia, with whom they are a close ally. Algeria is a member of the African Union, the Arab League, OPEC, the countrys name derives from the city of Algiers. The citys name in turn derives from the Arabic al-Jazāir, a form of the older Jazāir Banī Mazghanna. In the region of Ain Hanech, early remnants of hominid occupation in North Africa were found, neanderthal tool makers produced hand axes in the Levalloisian and Mousterian styles similar to those in the Levant. Algeria was the site of the highest state of development of Middle Paleolithic Flake tool techniques, tools of this era, starting about 30,000 BC, are called Aterian. The earliest blade industries in North Africa are called Iberomaurusian and this industry appears to have spread throughout the coastal regions of the Maghreb between 15,000 and 10,000 BC. Neolithic civilization developed in the Saharan and Mediterranean Maghreb perhaps as early as 11,000 BC or as late as between 6000 and 2000 BC and this life, richly depicted in the Tassili nAjjer paintings, predominated in Algeria until the classical period. The amalgam of peoples of North Africa coalesced eventually into a native population that came to be called Berbers. These settlements served as market towns as well as anchorages, as Carthaginian power grew, its impact on the indigenous population increased dramatically. Berber civilization was already at a stage in which agriculture, manufacturing, trade, by the early 4th century BC, Berbers formed the single largest element of the Carthaginian army. In the Revolt of the Mercenaries, Berber soldiers rebelled from 241 to 238 BC after being unpaid following the defeat of Carthage in the First Punic War. They succeeded in obtaining control of much of Carthages North African territory, the Carthaginian state declined because of successive defeats by the Romans in the Punic Wars
2.
Star and crescent
–
The star and crescent develops in the iconography of the Hellenistic period in Pontus, the Bosporan Kingdom, and notably Byzantium by the 2nd century BC. Coins with crescent and star symbols represented separately have a longer history, the star or Sun is often shown within the arc of the crescent, In numismatics in particular, the term crescent and pellet is used in cases where the star is simplified to a single dot. In Byzantium, the symbol became associated its patron goddess Artemis-Hecate, Ancient depictions of the symbol always show the crescent with horns pointing upward, and with the star placed inside the crescent. This arrangement is found on Sassanid coins beginning in the 5th or 6th century. The combination is found rarely in late medieval and early modern heraldry. It rose to prominence with its adoption as the flag and emblem of the Ottoman Empire and of some of its administrative divisions, and later in the 19th-century Westernizing tanzimat. The Ottoman flag of 1844 with a white ay-yıldız on a red background continues to be in use as the flag of the Republic of Turkey with minor modifications, other states formerly part of the Ottoman Empire also used the symbol, including Libya, Tunisia and Algeria. The same symbol was used in national flags introduced during the 20th century, including the flags of Azerbaijan, Pakistan, Malaysia, Singapore. Unicode introduced a star and crescent character in its Miscellaneous Symbols block, in Late Bronze Age Canaan, star and crescent moon motifs are also found on Moabite name seals. The depiction of the crescent-and-star or star inside crescent as it would develop in Bosporan Kingdom is difficult to trace to Mesopotamian art. An example of such an arrangement is found in the reconstruction of a fragmentary stele of Ur-Nammu discovered in the 1920s. Mithradates VI Eupator of Pontus used an eight rayed star with a crescent moon as his emblem, several possible interpretations of the emblem have been proposed. In most of these, the star is taken to represent the Sun, if any goddess had a connection with the walls in Constantinople, it was Hecate. Hecate had a cult in Byzantium from the time of its founding, like Byzas in one legend, she had her origins in Thrace. Hecate was considered the goddess of Byzantium because she was said to have saved the city from an attack by Philip of Macedon in 340 BC by the appearance of a bright light in the sky. To commemorate the event the Byzantines erected a statue of the known as the Lampadephoros. Some Byzantine coins of the 1st century BC and later show the head of Artemis with bow and quiver, the star and crescent symbol appears on some coins of the Parthan vassal kingdom of Elymais in the late 1st century AD. The same symbol is present in coins that are associated with Orodes I of Parthia
3.
Barbary pirates
–
This area was known in Europe as the Barbary Coast, a term derived from the name of its Berber inhabitants. The main purpose of their attacks was to capture Christian slaves for the Ottoman slave trade as well as the general Muslim slavery market in North Africa and the Middle East. In that period Algiers, Tunis and Tripoli came under the sovereignty of the Ottoman Empire, similar raids were undertaken from Salé and other ports in Morocco. Corsairs captured thousands of ships and repeatedly raided coastal towns, as a result, residents abandoned their former villages of long stretches of coast in Spain and Italy. The raids were such a problem coastal settlements were seldom undertaken until the 19th century, from the 16th to 19th century, corsairs captured an estimated 800,000 to 1.25 million people as slaves. Some corsairs were European outcasts and converts such as John Ward, Hayreddin Barbarossa and Oruç Reis, Turkish Barbarossa Brothers, who took control of Algiers on behalf of the Ottomans in the early 16th century, were also notorious corsairs. The European pirates brought advanced sailing and shipbuilding techniques to the Barbary Coast around 1600, the effects of the Barbary raids peaked in the early to mid-17th century. However, the ships and coasts of Christian states without such effective protection continued to suffer until the early 19th century. Following the Napoleonic Wars and the Congress of Vienna in 1814–15, European powers agreed upon the need to suppress the Barbary corsairs entirely and the threat was largely subdued. Occasional incidents occurred, including two Barbary wars between the United States and the Barbary States, until terminated by the French conquest of Algiers in 1830. Piracy by Muslim populations had been known in the Mediterranean since at least the 9th century, in the 14th century Tunisian corsairs became enough of a threat to provoke a Franco-Genoese attack on Mahdia in 1390, also known as the Barbary Crusade. The Barbary pirates had long attacked English and other European shipping along the North Coast of Africa and they had been attacking English merchant and passengers ships since the 1600s. Regular fundraising for ransoms was undertaken generally by families and local church groups, the government did not ransom ordinary persons. The English became familiar with captivity narratives written by Barbary pirates prisoners and ransomed captives, during the American Revolution the pirates attacked American ships. The Moroccan-American Treaty of Friendship stands as the U. S. s oldest non-broken friendship treaty with a foreign power, in 1778 Morocco became the first nation to recognize the new United States. As late as 1798, an islet near Sardinia was attacked by the Tunisians, throughout history, geography was on the pirates side on the Northern coast of Africa. The coast was ideal for their wants and needs, with natural harbours often backed by lagoons, it provided a haven for guerrilla warfare, such as attacks on shipping vessels venturing through their territory. On the coast, mountainous areas provided ample reconnaissance for the corsairs as well, ships were spotted from afar, the pirates had time to prepare their attacks and surprise the ships
4.
Laureys a Castro
–
Laureys a Castro or Lorenzo A. Castro was a Flemish painter of marine views and portraits who is mainly known for his work executed in England roughly between 1672 and 1700. He was regarded as a marine painter in England. There are very few details about Laureys a Castro’s life and training and it is assumed he was the son of the Flemish marine painter Sebastian Castro. His family was of Portuguese descent and had settled in Antwerp likely to escape the persecution of Jews during the Portuguese Inquisition of the early 1600s and it is assumed Laureys received his training from his father. Laureys is recorded as a wijnmeester in the Antwerp Guild of Saint Luke in 1664-65, based on the subjects of his paintings, he likely travelled and visited many Mediterranean ports such as Lisbon, Genoa, Malta and Sicily. Around 1670-72 he settled in England where he was active as a marine and it is not know when or where he died. No paintings are attributed to him after the end of the 17th century, a record of 1695 of “Lawrence Castro” in Whitecross Street, London and various works by an artist of that name in English collections suggest that Castro was at that time still working in England. Castro’s period of activity is given as 1664 to 1700 and 1672 to 1686. The latter, shorter period is based on the dated paintings of Castro. While Castro is mainly known for his paintings, he also painted portraits, religious subjects. These compositions show him to be steeped in Flemish and Dutch traditions of marine painting and his seascapes evidence a vigour and vividness of colour while some of his battle scenes are surprisingly calm. He created many renderings of naval battles and his earliest dated painting is a 1672 imaginary interpretation of the Battle of Actium and he painted a panoramic view of the Battle of Lepanto. This painting may have inspired by the frequently reproduced Dutch line engraving after Stradanus of 1590. It is likely that the relief after the retreat of the Turks before Vienna provided the impulse for this composition. Castro also depicted more contemporary naval engagements such as in his A Sea Fight with Barbary Corsairs, another frequently recurring theme of his compositions are capriccios of Mediterranean ports. It is likely that Castro was acquainted with Mediterranean ports such as Genoa, Malta, the ports depicted in these compositions are not always identifiable. The harbour town and the many persons onshore are painted in detail making it possible to recognize a Knight of Malta. Castro is also believed to have painted religious paintings as indicated by a drawing of a Virgin with Child, St John the Baptist and Angels in the Museum of Fine Arts, Ghent
5.
15th century
–
The 15th century was the century which spans the Julian years 1400 to 1500. In Europe, the 15th century is seen as the bridge between the Late Middle Ages, the Early Renaissance, and the Early modern period. Many technological, social and cultural developments of the 15th century can in retrospect be seen as heralding the European miracle of the following centuries, in religious history, the Roman Papacy was split in two parts in Europe for decades, until the Council of Constance. The division of the Catholic Church and the unrest associated with the Hussite movement would become factors in the rise of the Protestant Reformation in the following century. The event forced Western Europeans to find a new route, adding further momentum to what was the beginning of the Age of Discovery. Explorations by the Spanish and Portuguese led to European sightings of the Americas and these expeditions ushered in the era of the Portuguese and Spanish colonial empires. The fall of Constantinople led to the migration of Greek scholars and texts to Italy and these two events played key roles in the development of the Renaissance. The Spanish Reconquista leads to the fall of the Emirate of Granada by the end of the century, ending over seven centuries of Muslim rule. The Hundred Years War end with a decisive French victory over the English in the Battle of Castillon, financial troubles in England following the conflict results in the Wars of the Roses, a series of dynastic wars for the throne of England. The conflicts ends with the defeat of Richard III by Henry VII at the Battle of Bosworth Field, establishing the Tudor dynasty in the later part of the century. In Asia, under the rule of the Yongle Emperor, who built the Forbidden City and commanded Zheng He to explore the world overseas, tamerlane established a major empire in the Middle East and Central Asia, in order to revive the Mongol Empire. In Africa, the spread of Islam leads to the destruction of the Christian kingdoms of Nubia, the formerly vast Mali Empire teeters on the brink of collapse, under pressure from the rising Songhai Empire. In the Americas, both the Inca Empire and the Aztec Empire reach the peak of their influence, 1400s 1401, Dilawar Khan establishes the Malwa Sultanate in present-day central India 1402, Ottoman and Timurid Empires fight at the Battle of Ankara resulting in Timurs capture of Bayezid I. 1402, Sultanate of Malacca founded by Parameshwara,1403, The Yongle Emperor moves the capital of China from Nanjing to Beijing. 1403, The settlement of the Canary Islands signals the beginning of the Spanish Empire, 1405–1433, Zheng He of China sails through the Indian Ocean to India, Arabia, and East Africa to spread Chinas influence and sovereignty. 1405, Paregreg war, Majapahit civil war of succession between Wikramawardhana against Wirabhumi, 1405–1407, The first voyage of Zheng He, a massive Ming dynasty naval expedition visited Java, Palembang, Malacca, Aru, Samudera and Lambri. 1410s 1410, The Battle of Grunwald is the battle of the Polish–Lithuanian–Teutonic War leading to the downfall of the Teutonic Knights. 1410–1413, Foundation of St Andrews University in Scotland,1414, Khizr Khan, deputised by Timur to be the governor of Multan, takes over Delhi founding the Sayyid dynasty
6.
17th century
–
The 17th century was the century that lasted from January 1,1601, to December 31,1700, in the Gregorian calendar. The greatest military conflicts were the Thirty Years War, the Great Turkish War, in the Islamic world, the Ottoman, Safavid Persian and Mughal empires grew in strength. In Japan, Tokugawa Ieyasu established the Edo period at the beginning of the century, European politics were dominated by the Kingdom of France of Louis XIV, where royal power was solidified domestically in the civil war of the Fronde. With domestic peace assured, Louis XIV caused the borders of France to be expanded and it was during this century that English monarch became a symbolic figurehead and Parliament was the dominant force in government – a contrast to most of Europe, in particular France. It was also a period of development of culture in general,1600, On February 17 Giordano Bruno is burned at the stake by the Inquisition. 1600, Michael the Brave unifies the three Romanian countries, Wallachia, Moldavia and Transylvania after the Battle of Șelimbăr from 1599. 1601, Battle of Kinsale, England defeats Irish and Spanish forces at the town of Kinsale, driving the Gaelic aristocracy out of Ireland and destroying the Gaelic clan system. 1601, Michael the Brave, voivode of Wallachia, Moldavia and Transylvania, is assassinated by the order of the Habsburg general Giorgio Basta at Câmpia Turzii, 1601–1603, The Russian famine of 1601–1603 kills perhaps one-third of Russia. 1601, Panembahan Senopati, first king of Mataram, dies and passes rule to his son Panembahan Seda ing Krapyak 1601,1602, Matteo Ricci produces the Map of the Myriad Countries of the World, a world map that will be used throughout East Asia for centuries. 1602, The Portuguese send an expeditionary force from Malacca which succeeded in reimposing a degree of Portuguese control. 1602, The Dutch East India Company is established by merging competing Dutch trading companies and its success contributes to the Dutch Golden Age. 1602, Two emissaries from the Aceh Sultanate visit the Dutch Republic,1603, Elizabeth I of England dies and is succeeded by her cousin King James VI of Scotland, uniting the crowns of Scotland and England. 1603, Tokugawa Ieyasu takes the title of Shogun, establishing the Tokugawa Shogunate and this begins the Edo period, which will last until 1869. 1603–1623, After modernizing his army, Abbas I expands the Persian Empire by capturing territory from the Ottomans,1603, First permanent Dutch trading post is established in Banten, West Java. First successful VOC privateering raid on a Portuguese ship,1604, A second English East India Company voyage commanded by Sir Henry Middleton reaches Ternate, Tidore, Ambon and Banda. 1605, Gunpowder Plot failed in England,1605, The fortresses of Veszprém and Visegrad are retaken by the Ottomans. 1605, February, The VOC in alliance with Hitu prepare to attack a Portuguese fort in Ambon,1605, Panembahan Seda ing Krapyak of Mataram establishes control over Demak, former center of the Demak Sultanate. 1606, Treaty of Vienna ends anti-Habsburg uprising in Royal Hungary,1606, Assassination of Stephen Bocskay of Transylvania
7.
Crescent
–
A crescent shape is a symbol or emblem used to represent the lunar phase in the first quarter, or by extension a symbol representing the Moon itself. It is used as the symbol for the Moon. It was also the emblem of Diana-Artemis, and hence represented virginity, in Roman Catholic Marian veneration, it is associated with the Virgin Mary. From its use as roof finial in Ottoman era mosques, it has become associated with Islam. The crescent symbol is used to represent the Moon, not necessarily in a particular lunar phase. When used to represent a waxing or waning lunar phase, crescent or increscent refers to the waxing first quarter, the crescent symbol was long used as a symbol of the Moon in astrology, and by extension of Silver in alchemy. The astrological use of the symbol is attested in early Greek papyri containing horoscopes, in the 2nd-century Bianchinis planisphere, the personification of the Moon is shown with a crescent attached to her headdress. Its ancient association with Ishtar/Astarte and Diana is preserved in the Moon representing the female principle, as such, it belongs to the class of figures known as lune in planar geometry. The tapering towards the points of intersection of the two arcs are known as the horns of the crescent, the word crescent is derived etymologically from the present participle of the Latin verb crescere to grow, technically denoting the waxing moon. Unicode encodes a crescent at U+263D and a decrescent at U+263E, the Miscellaneous Symbols and Pictographs block provides variants with faces, FIRST QUARTER MOON WITH FACE at U+1F31B and LAST QUARTER MOON WITH FACE at U+1F31C. The crescent shape is used to represent the Moon, and the Moon deity Nanna/Sin from an early time, visible in Akkadian cylinder seals as early as 2300 BC. The crescent was used in the iconography of the Ancient Near East and was used transplanted by the Phoenicians in the 8th century BC as far as Carthage in modern Tunisia. The crescent and star also appears on coins of South Arabia. The combination of star and crescent also arises in the Ancient Near East, representing the Moon and Ishtar and it was inherited both in Sassanian and Hellenistic iconography. In the iconography of the Hellenistic period, the crescent became the symbol of Artemis-Diana, numerous depictions show Artemis-Diana wearing the crescent Moon as part of her headdress. The related symbol of the star and crescent was the emblem of the Mithradates dynasty in the Kingdom of Pontus and was used as the emblem of Byzantium. The crescent remained in use as an emblem in Sassanid Persia, in the Crusades it came to be associated with the Orient and was widely used in Crusader seals and coins. It was used as a charge by the later 13th century
8.
19th century
–
The 19th century was the century marked by the collapse of the Spanish, Napoleonic, Holy Roman and Mughal empires. After the defeat of the French Empire and its allies in the Napoleonic Wars, the Russian Empire expanded in central and far eastern Asia. By the end of the century, the British Empire controlled a fifth of the worlds land, the Industrial Revolution began in Great Britain and spread to continental Europe, North America and Japan. The Victorian era was notorious for the employment of children in factories and mines, as well as strict social norms regarding modesty. Japan embarked on a program of rapid modernization following the Meiji Restoration, before defeating China, under the Qing Dynasty, europes population doubled during the 19th century, from approximately 200 million to more than 400 million. Numerous cities worldwide surpassed populations of a million or more during this century, London became the worlds largest city and capital of the British Empire. Its population increased from 1 million in 1800 to 6.7 million a century later, liberalism became the pre-eminent reform movement in Europe. Slavery was greatly reduced around the world, following a successful slave revolt in Haiti, Britain and France stepped up the battle against the Barbary pirates and succeeded in stopping their enslavement of Europeans. The UKs Slavery Abolition Act charged the British Royal Navy with ending the slave trade. The first colonial empire in the century to abolish slavery was the British, americas 13th Amendment following their Civil War abolished slavery there in 1865, and in Brazil slavery was abolished in 1888. Similarly, serfdom was abolished in Russia, in the 19th century approximately 70 million people left Europe, with most migrating to the United States of America. The 19th century also saw the creation, development and codification of many sports, particularly in Britain. Also, ladywear was a sensitive topic during this time. 1801, Ranjit Singh crowned as King of Punjab,1801, Napoleon signs the Concordat of 1801 with the Pope. 1801, Cairo falls to the British,1801, Assassination of Tsar Paul I of Russia. 1802, Ludwig van Beethoven performs his Moonlight Sonata for the first time,1803, William Symington demonstrates his Charlotte Dundas, the first practical steamboat. 1803, The United States more than doubles in size when it buys out Frances territorial claims in North America via the Louisiana Purchase. This begins the U. S. s westward expansion to the Pacific referred to as its Manifest Destiny which involves annexing and conquering land from Mexico, Britain,1803, The Wahhabis of the First Saudi State capture Mecca and Medina
9.
Algerian National Navy
–
The Algerian National Navy is the naval branch of the Military of Algeria. Additional missions include coast guard and maritime safety missions as well a projection of marine forces, Algerian forces are an important player in the Western Mediterranean. Since the end of the Cold War, Russia has remained an important partner, the origins of the Algerian Navy ) At that time the Maghreb under the control of the Almohad dynasty which also ruled the current Spain al-Andalus and 1147 to 1269. The Navy was born with the installation by Abd El Moumen naval shipyards the Almohad empire in the ports of Oran, but the reign of this great dynasty would soon be glazed at first by a few internal disagreements, mainly related to the difficulties of managing a vast territory. He moved later to head its fleet to Algeria to its liberation from the Spanish colonization, from there a new page was opened for Algeria which through its Marine could impose its leadership in the Mediterranean for nearly three centuries. However the Algerian armada also lost a number of vessels. Some Algerian squadrons took part to the Greek war of independence from 1821 on, as suppletive forces to the Ottoman fleet, in June 1827, Charles X launched a naval blockade on Algiers and three years later a military expedition which finally took the city in 1830. Algeria, endured for a century and 32 years of French rule until July 5,1962, principal naval bases are located at Algiers, Annaba, Mers el-Kebir, Oran, Jijel and Tamentfoust. Mers el Kébir is home to the OMCN/CNE shipbuilding facilities where several Algerian vessels have been built, algerias naval academy at Tamentfoust provides officer training equivalent to that of the army and the air force academies. The navy also operates a training school for its personnel at Tamentfoust. The bulk of the Algerian Navy is still based on Cold War designs, the surface fleet is equipped with a mixture of smaller ships well suited to coastal and Exclusive Economic Zone patrol work. The fleet is led by three Koni class frigates which have been updated with modern systems. A mixture of six corvettes and off-shore patrol vessels complement the frigates, Algeria had maintained a relatively large fleet of Osa class fast attack craft by the end of the Cold War, but it is questionable whether any of these remain in operational use. Their amphibious warfare capacity has traditionally been limited with a group of landing ships essentially for coastal transport roles. This capacity will be upgraded with the planned acquisition of an amphibious transport dock capable of supporting more robust operations. The Algerian military has maintained a strong veil of secrecy over its organization and equipment. Open sources are known to vary widely in their reports of several aspects of Algerian equipment, the Navy is currently being upgraded with the following technological developments, the existing units are being modernized, with the submarine force strengthened by two new Kilo class submarines. One LPD form Italy in 2014, four MEKO A200 frigates from Germany
10.
Wavelength
–
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the waves shape repeats, and thus the inverse of the spatial frequency. Wavelength is commonly designated by the Greek letter lambda, the concept can also be applied to periodic waves of non-sinusoidal shape. The term wavelength is also applied to modulated waves. Wavelength depends on the medium that a wave travels through, examples of wave-like phenomena are sound waves, light, water waves and periodic electrical signals in a conductor. A sound wave is a variation in air pressure, while in light and other electromagnetic radiation the strength of the electric, water waves are variations in the height of a body of water. In a crystal lattice vibration, atomic positions vary, wavelength is a measure of the distance between repetitions of a shape feature such as peaks, valleys, or zero-crossings, not a measure of how far any given particle moves. For example, in waves over deep water a particle near the waters surface moves in a circle of the same diameter as the wave height. The range of wavelengths or frequencies for wave phenomena is called a spectrum, the name originated with the visible light spectrum but now can be applied to the entire electromagnetic spectrum as well as to a sound spectrum or vibration spectrum. In linear media, any pattern can be described in terms of the independent propagation of sinusoidal components. The wavelength λ of a sinusoidal waveform traveling at constant speed v is given by λ = v f, in a dispersive medium, the phase speed itself depends upon the frequency of the wave, making the relationship between wavelength and frequency nonlinear. In the case of electromagnetic radiation—such as light—in free space, the speed is the speed of light. Thus the wavelength of a 100 MHz electromagnetic wave is about, the wavelength of visible light ranges from deep red, roughly 700 nm, to violet, roughly 400 nm. For sound waves in air, the speed of sound is 343 m/s, the wavelengths of sound frequencies audible to the human ear are thus between approximately 17 m and 17 mm, respectively. Note that the wavelengths in audible sound are much longer than those in visible light, a standing wave is an undulatory motion that stays in one place. A sinusoidal standing wave includes stationary points of no motion, called nodes, the upper figure shows three standing waves in a box. The walls of the box are considered to require the wave to have nodes at the walls of the box determining which wavelengths are allowed, the stationary wave can be viewed as the sum of two traveling sinusoidal waves of oppositely directed velocities. Consequently, wavelength, period, and wave velocity are related just as for a traveling wave, for example, the speed of light can be determined from observation of standing waves in a metal box containing an ideal vacuum. In that case, the k, the magnitude of k, is still in the same relationship with wavelength as shown above
11.
RGB color model
–
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
12.
CMYK color model
–
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
.svg)
Media related to Flags of Algeria at Wikimedia Commons
