Structure.

In the majority of silicates, the silicon atom shows tetrahedral coordination, with four oxygen atoms surrounding a central Si atom. The most common example is seen in the quartz polymorphs. It is a 3 dimensional network solid in which each silicon atom is covalently bonded in a tetrahedral manner to 4 oxygen atoms.  For example, in the unit cell of α-quartz, the central tetrahedron shares all four of its corner O atoms, the two face-centered tetrahedra share two of their corner O atoms, and the four edge-centered tetrahedra share just one of their O atoms with other SiO tetrahedra. This leaves a net average of 12 out of 24 total vertices for that portion of the seven SiO tetrahedra that are considered to be a part of the unit cell for silica (see 3-D Unit Cell).  SiO has a number of distinct crystalline forms (polymorphs) in addition to amorphous forms. With the exception of stishovite and fibrous silica, all of the crystalline forms involve tetrahedral SiO units linked together by shared vertices. Silicon–oxygen bond lengths vary between the various crystal forms; for example in α-quartz the bond length is 161 pm, whereas in α-tridymite it is in the range 154–171 pm. The Si-O-Si angle also varies between a low value of 140° in α-tridymite, up to 180° in β-tridymite. In α-quartz, the Si-O-Si angle is 144°.  Fibrous silica has a structure similar to that of SiS with chains of edge-sharing SiO tetrahedra. Stishovite, the higher-pressure form, in contrast, has a rutile-like structure where silicon is 6-coordinate. The density of stishovite is 4.287 g/cm, which compares to α-quartz, the densest of the low-pressure forms, which has a density of 2.648 g/cm. The difference in density can be ascribed to the increase in coordination as the six shortest Si-O bond lengths in stishovite (four Si-O bond lengths of 176 pm and two others of 181 pm) are greater than the Si-O bond length (161 pm) in α-quartz. The change in the coordination increases the ionicity of the Si-O bond. More importantly, any deviations from these standard parameters constitute microstructural differences or variations, which represent an approach to an amorphous, vitreous, or glassy solid.  The only stable form under normal conditions is alpha quartz, in which crystalline silicon dioxide is usually encountered. In nature, impurities in crystalline α-quartz can give rise to colors (see list). The high-temperature minerals, cristobalite and tridymite, have both lower densities and indices of refraction than quartz. Since the composition is identical, the reason for the discrepancies must be in the increased spacing in the high-temperature minerals. As is common with many substances, the higher the temperature, the farther apart the atoms are, due to the increased vibration energy.  The transformation from α-quartz to beta-quartz takes place abruptly at 573 °C. Since the transformation is accompanied by a significant change in volume, it can easily induce fracturing of ceramics or rocks passing through this temperature limit.  The high-pressure minerals, seifertite, stishovite, and coesite, though, have higher densities and indices of refraction than quartz. This is probably due to the intense compression of the atoms occurring during their formation, resulting in more condensed structure.  Faujasite silica is another form of crystalline silica. It is obtained by dealumination of a low-sodium, ultra-stable Y zeolite with combined acid and thermal treatment. The resulting product contains over 99% silica, and has high crystallinity and surface area (over 800 m/g). Faujasite-silica has very high thermal and acid stability. For example, it maintains a high degree of long-range molecular order or crystallinity even after boiling in concentrated hydrochloric acid.  Molten silica exhibits several peculiar physical characteristics that are similar to those observed in liquid water: negative temperature expansion, density maximum at temperatures ~5000 °C, and a heat capacity minimum. Its density decreases from 2.08 g/cm at 1950 °C to 2.03 g/cm at 2200 °C.  Molecular SiO with a linear structure is produced when molecular silicon monoxide, SiO, is condensed in an argon matrix cooled with helium along with oxygen atoms generated by microwave discharge. Dimeric silicon dioxide, (SiO) has been prepared by reacting O with matrix isolated dimeric silicon monoxide, (SiO). In dimeric silicon dioxide there are two oxygen atoms bridging between the silicon atoms with an Si-O-Si angle of 94° and bond length of 164.6 pm and the terminal Si-O bond length is 150.2 pm. The Si-O bond length is 148.3 pm, which compares with the length of 161 pm in α-quartz. The bond energy is estimated at 621.7 kJ/mol.

Natural occurrence.

Geology.

Silica with the chemical formula is most commonly found in nature as quartz, which comprises more than 10% by mass of the earth's crust. Quartz is the only polymorph of silica stable at the Earth's surface. Metastable occurrences of the high-pressure forms coesite and stishovite have been found around impact structures and associated with eclogites formed during ultra-high-pressure metamorphism. The high-temperature forms of tridymite and cristobalite are known from silica-rich volcanic rocks. In many parts of the world, silica is the major constituent of sand.. The various forms of silicon dioxide can be converted from one form to another by heating and changes in pressure.

Biology.

Even though it is poorly soluble, silica occurs in many plants. Plant materials with high silica phytolith content appear to be of importance to grazing animals, from chewing insects to ungulates. Silica accelerates tooth wear, and high levels of silica in plants frequently eaten by herbivores may have developed as a defense mechanism against predation.  Silica is also the primary component of rice husk ash, which is used, for example, in filtration and cement manufacturing.  For well over a billion years, silicification in and by cells has been common in the biological world. In the modern world it occurs in bacteria, single-celled organisms, plants, and animals (invertebrates and vertebrates). Prominent examples include:  Crystalline minerals formed in the physiological environment often show exceptional physical properties (e.g., strength, hardness, fracture toughness) and tend to form hierarchical structures that exhibit microstructural order over a range of scales. The minerals are crystallized from an environment that is undersaturated with respect to silicon, and under conditions of neutral pH and low temperature (0–40 °C).  Formation of the mineral may occur either within the cell wall of an organism (such as with phytoliths), or outside the cell wall, as typically happens with tests. Specific biochemical reactions exist for mineral deposition. Such reactions include those that involve lipids, proteins, and carbohydrates.  It is unclear in what ways silica is important in the nutrition of animals. This field of research is challenging because silica is ubiquitous and in most circumstances dissolves in trace quantities only. All the same it certainly does occur in the living body, leaving us with the problem that it is hard to create proper silica-free controls for purposes of research. This makes it difficult to be sure when the silica present has had operative beneficial effects, and when its presence is coincidental, or even harmful. The current consensus is that it certainly seems important in the growth, strength, and management of many connective tissues. This is true not only for hard connective tissues such as bone and tooth but possibly in the biochemistry of the subcellular enzyme-containing structures as well.

Uses.

Structural use.

About 95% of the commercial use of silicon dioxide (sand) occurs in the construction industry, e.g. for the production of concrete (Portland cement concrete).  Silica, in the form of sand is used as the main ingredient in sand casting for the manufacture of metallic components in engineering and other applications. The high melting point of silica enables it to be used in such applications.  Crystalline silica is used in hydraulic fracturing of formations which contain tight oil and shale gas.

Precursor to glass and silicon.

Silica is the primary ingredient in the production of most glass. The glass transition temperature of pure SiO is about 1475 K. When molten silicon dioxide SiO is rapidly cooled, it does not crystallize, but solidifies as a glass.  The structural geometry of silicon and oxygen in glass is similar to that in quartz and most other crystalline forms of silicon and oxygen with silicon surrounded by regular tetrahedra of oxygen centers. The difference between the glass and crystalline forms arises from the connectivity of the tetrahedral units: Although there is no long range periodicity in the glassy network ordering remains at length scales well beyond the SiO bond length. One example of this ordering is the preference to form rings of 6-tetrahedra.

Fumed silica.

Fumed silica also known as pyrogenic silica is a very fine particulate or colloidal form of silicon dioxide. It is prepared by burning SiCl in an oxygen-rich hydrogen flame to produce a "smoke" of SiO.  The majority of optical fibers for telecommunication are also made from silica. It is a primary raw material for many ceramics such as earthenware, stoneware, and porcelain.  Silicon dioxide is used to produce elemental silicon. The process involves carbothermic reduction in an electric arc furnace:

Food and pharmaceutical applications.

Silica is a common additive in food production, where it is used primarily as a flow agent in powdered foods, or to adsorb water in hygroscopic applications. It is used as an anti-caking agent in powdered foods such as spices and non-dairy coffee creamer. It is the primary component of diatomaceous earth. Colloidal silica is also used as a wine, beer, and juice fining agent. It has the E number reference E551.  In pharmaceutical products, silica aids powder flow when tablets are formed.

Personal care.

In cosmetics, it is useful for its light-diffusing properties and natural absorbency.  Hydrated silica is used in toothpaste as a hard abrasive to remove tooth plaque.

Semiconductors.

Silicon dioxide could be grown on a silicon semiconductor surface. Silicon oxide layers could protect silicon surfaces during diffusion processes, and could be used for diffusion masking.  Surface passivation is the process by which a semiconductor surface is rendered inert, and does not change semiconductor properties as a result of interaction with air or other materials in contact with the surface or edge of the crystal. The formation of a thermally grown silicon dioxide layer greatly reduces the concentration of electronic states at the silicon surface. SiO films preserve the electrical characteristics of p–n junctions and prevent these electrical characteristics from deteriorating by the gaseous ambient environment. Silicon oxide layers could be used to electrically stabilize silicon surfaces. The surface passivation process is an important method of semiconductor device fabrication that involves coating a silicon wafer with an insulating layer of silicon oxide so that electricity could reliably penetrate to the conducting silicon below. Growing a layer of silicon dioxide on top of a silicon wafer enables it to overcome the surface states that otherwise prevent electricity from reaching the semiconducting layer.  The process of silicon surface passivation by thermal oxidation (silicon dioxide) is critical to the semiconductor industry. It is commonly used to manufacture metal-oxide-semiconductor field-effect transistors (MOSFETs) and silicon integrated circuit chips (with the planar process).

Other.

Hydrophobic silica is used as a defoamer component.  In its capacity as a refractory, it is useful in fiber form as a high-temperature thermal protection fabric.  Silica is used in the extraction of DNA and RNA due to its ability to bind to the nucleic acids under the presence of chaotropes.  A silica-based aerogel was used in the Stardust spacecraft to collect extraterrestrial particles.  Pure silica (silicon dioxide), when cooled as fused quartz into a glass with no true melting point, can be used as a glass fiber for fiberglass.

Production.

Silicon dioxide is mostly obtained by mining, including sand mining and purification of quartz. Quartz is suitable for many purposes, while chemical processing is required to make a purer or otherwise more suitable (e.g. more reactive or fine-grained) product.

Silica fume.

Silica fume is obtained as byproduct from hot processes like ferrosilicon production. It is less pure than fumed silica and should not be confused with that product. The production process, particle characteristics, and fields of application of fumed silica differ from those of silica fume.

Precipitated silica.

Precipitated silica or amorphous silica is produced by the acidification of solutions of sodium silicate. The gelatinous precipitate or silica gel, is first washed and then dehydrated to produce colorless microporous silica. The idealized equation involving a trisilicate and sulfuric acid is:  Approximately one billion kilograms/year (1999) of silica were produced in this manner, mainly for use for polymer composites – tires and shoe soles.

On microchips.

Thin films of silica grow spontaneously on silicon wafers via thermal oxidation, producing a very shallow layer of about 1 nm or 10 Å of so-called native oxide. Higher temperatures and alternative environments are used to grow well-controlled layers of silicon dioxide on silicon, for example at temperatures between 600 and 1200 °C, using so-called dry oxidation with O  or wet oxidation with HO.  The native oxide layer is beneficial in microelectronics, where it acts as electric insulator with high chemical stability. It can protect the silicon, store charge, block current, and even act as a controlled pathway to limit current flow.

Laboratory or special methods.

From organosilicon compounds.

Many routes to silicon dioxide start with an organosilicon compound, e.g., HMDSO, TEOS. Synthesis of silica is illustrated below using tetraethyl orthosilicate (TEOS). Simply heating TEOS at 680–730 °C results in the oxide:  Similarly TEOS combusts around 400 °C:  TEOS undergoes hydrolysis via the so-called sol-gel process. The course of the reaction and nature of the product are affected by catalysts, but the idealized equation is:

Other methods.

Being highly stable, silicon dioxide arises from many methods. Conceptually simple, but of little practical value, combustion of silane gives silicon dioxide. This reaction is analogous to the combustion of methane:  However the chemical vapor deposition of silicon dioxide onto crystal surface from silane had been used using nitrogen as a carrier gas at 200–500 °C.

Chemical reactions.

Silica is converted to silicon by reduction with carbon.  Fluorine reacts with silicon dioxide to form SiF and O whereas the other halogen gases (Cl, Br, I) are essentially unreactive.  Silicon dioxide is attacked by hydrofluoric acid (HF) to produce hexafluorosilicic acid:  HF is used to remove or pattern silicon dioxide in the semiconductor industry.  Under normal conditions, silicon does not react with most acids but is dissolved by hydrofluoric acid. Silicon is attacked by bases such as aqueous sodium hydroxide to give silicates.  Silicon dioxide acts as a Lux–Flood acid, being able to react with bases under certain conditions. As it does not contain any hydrogen, it cannot act as a Brønsted–Lowry acid. While not soluble in water, some strong bases will react with glass and have to be stored in plastic bottles as a result.  Silicon dioxide dissolves in hot concentrated alkali or fused hydroxide, as described in this idealized equation:  Silicon dioxide will neutralise basic metal oxides (e.g. sodium oxide, potassium oxide, lead(II) oxide, zinc oxide, or mixtures of oxides, forming silicates and glasses as the Si-O-Si bonds in silica are broken successively). As an example the reaction of sodium oxide and SiO can produce sodium orthosilicate, sodium silicate, and glasses, dependent on the proportions of reactants:  Examples of such glasses have commercial significance, e.g. soda-lime glass, borosilicate glass, lead glass. In these glasses, silica is termed the network former or lattice former. The reaction is also used in blast furnaces to remove sand impurities in the ore by neutralisation with calcium oxide, forming calcium silicate slag. Silicon dioxide reacts in heated reflux under dinitrogen with ethylene glycol and an alkali metal base to produce highly reactive, pentacoordinate silicates which provide access to a wide variety of new silicon compounds. The silicates are essentially insoluble in all polar solvent except methanol.  Silicon dioxide reacts with elemental silicon at high temperatures to produce SiO:

Water solubility.

The solubility of silicon dioxide in water strongly depends on its crystalline form and is three-four times higher for silica than quartz; as a function of temperature, it peaks around 340 °C. This property is used to grow single crystals of quartz in a hydrothermal process where natural quartz is dissolved in superheated water in a pressure vessel that is cooler at the top. Crystals of 0.5–1 kg can be grown over a period of 1–2 months. These crystals are a source of very pure quartz for use in electronic applications.

Health effects.

Silica ingested orally is essentially nontoxic, with an of 5000 mg/kg (5 g/kg). A 2008 study following subjects for 15 years found that higher levels of silica in water appeared to decrease the risk of dementia. An increase of 10 mg/day of silica in drinking water was associated with a decreased risk of dementia of 11%.  Inhaling finely divided crystalline silica dust can lead to silicosis, bronchitis, or lung cancer, as the dust becomes lodged in the lungs and continuously irritates the tissue, reducing lung capacities. When fine silica particles are inhaled in large enough quantities (such as through occupational exposure), it increases the risk of systemic autoimmune diseases such as lupus and rheumatoid arthritis compared to expected rates in the general population.

Occupational hazard.

Silica is an occupational hazard for people who do sandblasting, or work with products that contain powdered crystalline silica. Amorphous silica, such as fumed silica, may cause irreversible lung damage in some cases, but is not associated with development of silicosis. Children, asthmatics of any age, those with allergies, and the elderly (all of whom have reduced lung capacity) can be affected in less time.  Crystalline silica is an occupational hazard for those working with stone countertops, because the process of cutting and installing the countertops creates large amounts of airborne silica. Crystalline silica used in hydraulic fracturing presents a health hazard to workers.

Pathophysiology.

In the body, crystalline silica particles do not dissolve over clinically relevant periods. Silica crystals inside the lungs can activate the NLRP3 inflammasome inside macrophages and dendritic cells and thereby result in production of interleukin, a highly pro-inflammatory cytokine in the immune system.

Regulation.

Regulations restricting silica exposure 'with respect to the silicosis hazard' specify that they are concerned only with silica, which is both crystalline and dust-forming.  In 2013, the U.S. Occupational Safety and Health Administration reduced the exposure limit to 50 μg/m of air. Prior to 2013, it had allowed 100 μg/m and in construction workers even 250 μg/m. In 2013, OSHA also required "green completion" of fracked wells to reduce exposure to crystalline silica besides restricting the limit of exposure.

Crystalline forms.

SiO, more so than almost any material, exists in many crystalline forms. These forms are called polymorphs.

Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula, most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and most abundant families of materials, existing as a compound of several minerals and as synthetic product. Notable examples include fused quartz, fumed silica, silica gel, and aerogels. It is used in structural materials, microelectronics (as an electrical insulator), and as components in the food and pharmaceutical industries.

Oxid křemičitý (SiO) tvoří nejméně 22 fází a dvanáct polymorfních forem. Díky této rozmanitosti a velkému praktickému významu patří tento oxid mezi nejstudovanější látky.


History.

The modern forum originated from bulletin boards, and so-called computer conferencing systems, and are a technological evolution of the dialup bulletin board system. From a technological standpoint, "forums" or "boards" are web applications managing user-generated content.  Early Internet forums could be described as a web version of an electronic mailing list or newsgroup (such as exist on Usenet); allowing people to post messages and comment on other messages. Later developments emulated the different newsgroups or individual lists, providing more than one forum, dedicated to a particular topic.  Internet forums are prevalent in several developed countries. Japan posts the most with over two million per day on their largest forum, 2channel. China also has many millions of posts on forums such as Tianya Club.  Some of the very first forum systems were the Planet-Forum system, developed at the beginning of the 1970-s, the EIES system, first operational in 1976, and the KOM system, first operational in 1977.  One of the first forum sites (which is still active today) is Delphi Forums, once called Delphi. The service, with four million members, dates to 1983.  Forums perform a function similar to

Structure.

A forum consists of a tree-like directory structure. The top end is "Categories". A forum can be divided into categories for the relevant discussions. Under the categories are sub-forums and these sub-forums can further have more sub-forums. The "topics" (commonly called "threads") come under the lowest level of sub-forums and these are the places under which members can start their discussions or "posts". Logically forums are organized into a finite set of generic topics (usually with one main topic) driven and updated by a group known as "members", and governed by a group known as "moderators". It can also have a graph structure. All message boards will use one of three possible display formats. Each of the three basic message board display formats: Non-Threaded/Semi-Threaded/Fully Threaded, has its own advantages and disadvantages. If messages are not related to one another at all, a Non-Threaded format is best. If a user has a message topic and multiple replies to that message topic, a semi-threaded format is best. If a user has a message topic and replies to that message topic and responds to replies, then a fully threaded format is best.

User groups.

Internally, Western-style forums organize visitors and logged in members into user groups. Privileges and rights are given based on these groups. A user of the forum can automatically be promoted to a more privileged user group based on criteria set by the administrator. A person viewing a closed thread as a "member" will see a box saying he does not have the right to submit messages there, but a "moderator" will likely see the same box granting him access to more than just posting messages.  An

Moderators.

The "moderators" (short singular form: "mod") are users (or employees) of the forum who are granted access to the posts and threads of all members for the purpose of "moderating discussion" (similar to arbitration) and also keeping the forum clean (neutralizing spam and spambots etc.). Moderators also answer users' concerns about the forum, general questions, as well as respond to specific complaints. Common privileges of moderators include: deleting, merging, moving, and splitting

Administrator.

The "administrators" (short form: "admin") manage the technical details required for running the site. As such, they may promote (and demote) members to/from moderators, manage the rules, create sections and sub-sections, as well as perform any database operations (database backup etc.). Administrators often also act as moderators. Administrators may also make forum-wide announcements, or change the appearance (known as the skin) of a forum. There are also many forums where administrators share their knowledge.

Post.

A "post" is a user-submitted message enclosed into a block containing the user's details and the date and time it was submitted. Members are usually allowed to edit or delete their own posts. Posts are contained in threads, where they appear as blocks one after another. The first post starts the thread; this may be called the TS (thread starter) or OP (original post). Posts that follow in the thread are meant to continue discussion about that post, or respond to other replies; it is not uncommon for discussions to be derailed.  On Western forums, the classic way to show a member's own details (such as name and avatar)

Thread.

A "thread" (sometimes called a "topic") is a collection of posts, usually displayed from oldest to latest, although this is typically configurable: Options for newest to oldest and for a threaded view (a tree-like view applying logical reply structure before chronological order) can be available. A thread is defined by a title, an additional description that may summarize the intended discussion, and an opening or original post (common abbreviation OP, which can also mean original poster), which opens whatever dialogue or makes whatever announcement the poster wished. A thread can contain any number of posts, including multiple posts from the same members, even if they are one after the other.

Bumping.

A thread is contained in a forum and may have an associated date that is taken as the date of the last post (options to order threads by other criteria are generally available). When a member posts in a thread it will jump to the top since it is the latest updated thread. Similarly, other threads will jump in front of it when they receive posts. When a member posts

Stickying.

Threads that are important but rarely receive posts are "sticky"ed (or, in some software, "pinned"). A "sticky thread" will always appear in front of normal threads, often in its own section. A "threaded discussion group" is simply any group of individuals who use a forum for threaded, or asynchronous, discussion purposes. The group may or may not be the only users of the forum.  A thread's popularity is measured on forums in reply (total posts minus one, the opening post, in most default forum settings) counts. Some forums also track page views. Threads meeting a set number of posts or a set number of views may receive a designation such as "hot thread" and be displayed with a different icon compared to other threads. This icon may stand out more to emphasize the thread. If the forum's users have lost interest in a particular thread, it becomes a "dead thread".

Discussion.

Forums prefer a premise of open and free discussion and often adopt de facto standards. Most common topics on forums include questions, comparisons, polls of opinion, as well as debates. It is not uncommon for nonsense or unsocial behavior to sprout as people lose temper, especially if the topic is controversial. Poor understanding of differences in values of the participants is a common problem on forums. Because replies to a topic are often worded aimed at someone's point of view, discussion will usually go slightly off into several directions as people question each other's validity, sources and so on. Circular discussion and ambiguity in replies can extend for several tens of posts of a thread eventually ending when everyone gives up or attention spans waver and a more interesting subject takes over. It is not uncommon for debate to end in ad hominem attacks.

Liabilities of owners and moderators.

Several lawsuits have been brought against the forums and moderators claiming libel and damage. A recent case is the scubaboard lawsuit where a business in the Maldives filed a suit against scubaboard for libel and defamation in

Common features.

By default to be an Internet forum, the web application needs an ability to submit threads and replies. Typically, threads are in newer to older view, and replies in older to newer view.

Tripcodes and capcodes.

Most imageboards and 2channel-style discussion boards allow (and encourage) anonymous posting and use a system of tripcodes instead of registration. A tripcode is the hashed result of a password that allows one's identity to be recognized without storing any data about users.  In a tripcode system, a secret password is added to the user's name following a separator

Private message.

A "private message", or PM for short, is a message sent in private from a member to one or more other members. The ability to send so-called blind carbon copies is sometimes available. When sending a "blind carbon copy" (bcc), the users

Attachment.

An attachment can be almost any file. When someone attaches a file to a person's post they are uploading that particular file to the

BBCode and HTML.

HyperText Markup Language (HTML) is sometimes allowed but usually its use is discouraged or when allowed, it is extensively filtered. Modern bulletin board systems often will have it disabled altogether or allow only administrators use it, as allowing it on any normal user level is considered a security risk due to a high rate of XSS vulnerabilities. When HTML is disabled Bulletin Board Code (BBCode) is the most common preferred alternative. BBCode usually consists of a tag, similar to HTML only instead of codice_1

Emoticon.

An emoticon or "smiley" is a symbol or combination of symbols used to convey emotional content in written or message form. Forums implement a system through which some of the text representations of an emoticons

Poll.

Most forums implement an opinion poll system for threads. Most implementations allow for single-choice or multi-choice (sometimes limited to a certain number) when selecting options as well

RSS and ATOM.

RSS and ATOM feeds allow a minimalistic means of subscribing to the forum. Common implementations

Other features.

An "ignore list" allows members to hide posts of other members that they do not want to see or have a problem with. In most implementations, they are referred to as "foe list" or "ignore list". The posts are usually not hidden, but minimized with only a small bar indicating a post from the user on the "ignore list" is there. Almost all Internet forums include a "member list", which allows display of all forum members, with an integrated search feature.

Rules and policies.

Forums are governed by a set of individuals, collectively referred to as "staff", made up of "administrators" and "moderators", which are responsible for the forums' conception, technical maintenance, and policies (creation and enforcing). Most forums have a list of rules detailing the wishes, aim, and guidelines of the forums' creators. There is usually also a FAQ section containing basic information for new members and people not yet familiar with the use and principles of a forum (generally tailored for specific forum software).  Rules on forums usually apply to the entire user body and often have preset exceptions, most commonly designating a section as an exception. For example, in an IT forum any discussion regarding anything but computer programming languages may be against the rules, with the exception of a "general chat" section.  Forum rules are maintained and enforced by the moderation team, but users are allowed to help out via what is known as a report system. Most Western forum platforms automatically provide such a system. It consists of a small function applicable to each post (including one's own). Using it will notify all currently available moderators of its location, and subsequent action or judgment can be carried out immediately, which is particularly desirable in large or very developed boards. Generally, moderators encourage members to also use the "private message" system if they wish to report behavior. Moderators will generally frown upon attempts of moderation by non-moderators, especially when the would-be moderators do not even issue a report. Messages from non-moderators acting as moderators generally declare a post as against the rules or predict punishment. While not harmful, statements that attempt to enforce the rules are discouraged.  When rules are broken several steps are commonly taken. First, a warning is usually given; this is commonly in the form of a "private message" but recent development has made it possible for it to be integrated into the software. Subsequent to this, if the act is ignored and warnings do not work, the member is – usually – first exiled from the forum for a number of days. Denying someone access to the site is called a "ban". Bans can mean the person can no longer log in or even view the site anymore. If the offender, after the warning sentence, repeats the offense, another ban is given, usually this time a longer one. Continuous harassment of the site eventually leads to a permanent ban. In most cases, this means simply that the account is locked. In extreme cases where the offender – after being permanently banned – creates another account and continues to harass the site, administrators will apply an IP address ban or block (this can also be applied at the server level): If the IP address is static, the machine of the offender is prevented from accessing the site. In some extreme circumstances, IP address range bans or country bans can be applied; this is usually for political, licensing, or other reasons. See also: Block (Internet), IP address blocking, and Internet censorship.  Offending content is usually deleted. Sometimes if the topic is considered the source of the problem, it is "locked"; often a poster may request a topic expected to draw problems to be locked as well, although the moderators decide whether to grant it. In a "locked thread", members cannot post anymore. In cases where the topic is considered a breach of rules it – with all of its posts – may be deleted.

Comparison with other web applications.

Electronic mailing lists: The main difference between forums and electronic mailing lists is that mailing lists automatically deliver new messages to the subscriber, while forums require the reader to visit the website and check for new posts. Because members may miss replies in threads they are interested in, many modern forums offer an "e-mail notification" feature, whereby members can choose to be notified of new posts in a thread, and web feeds that allow members to see a summary of the new posts using aggregator software. There are also software products that combine forum and mailing list features, i.e. posting and reading via email as well as the browser depending on the member's choice.  Newsreader: The main difference between newsgroups and forums is that additional software, a News client, is required to participate in newsgroups whereas using a forum requires no additional software beyond the web browser.  Shoutboxes: Unlike Internet forums, most shoutboxes do not require registration, only requiring an email address from the user. Additionally, shoutboxes are not heavily moderated, unlike most message boards.  Wiki: Unlike conventional forums, the original wikis allowed all users to edit all content (including each other's messages). This level of content manipulation is reserved for moderators or administrators on most forums. Wikis also allow the creation of other content outside the talk pages. On the other hand, weblogs and generic content management systems tend to be locked down to the point where only a few select users can post blog entries, although many allow other users to comment upon them. The Wiki hosting site known as Wikia has two features in operation, known as the Forum and Message Wall. The forum is used solely for discussion and works through editing, while the message wall works through posted messages more similar to a traditional forum.  Chat rooms and instant messaging: Forums differ from chats and instant messaging in that forum participants do not have to be online simultaneously to receive or send messages. Messages posted to a forum are publicly available for some time even if the forum or thread is closed, which is uncommon in chat rooms that maintain frequent activity.  One rarity among forums is the ability to create a picture album. Forum participants may upload personal pictures onto the site and add descriptions to the pictures. Pictures may be in the same format as posting threads, and contain the same options such as "Report Post" and "Reply to Post".

An Internet forum, or message board, is an online discussion site where people can hold conversations in the form of posted messages. They differ from chat rooms in that messages are often longer than one line of text, and are at least temporarily archived. Also, depending on the access level of a user or the forum set-up, a posted message might need to be approved by a moderator before it becomes publicly visible.

Internetová diskuse je stránka (místo) na internetu, kam lidé vkládají své názory a reakce a ty se následně na stránce zobrazují. Oproti IRC kanálům nebo chatu se internetová diskuse obvykle liší tím, že přispěvatelé nemusí být ke stránce připojeni současně a reagovat bezprostředně, ale mohou reagovat i s odstupem mnoha dní či měsíců. V diskusích se obvykle nehraje na slušnost a je zcela běžné vulgární nadávání, pomluvy, přirovnávání k Hitlerovi, hádky, vzájemné napadání, extremistické příspěvky, vyhrožování policií. Lidé si myslí, že jsou anonymní, ale přitom není problém je vystopovat.


Geography.

This region with a long history is situated in the southwest of Slovakia, mostly in the eastern part of the Danubian Lowland. It is divided into two sub-units: the Danubian Flat in the south-west, with eastern part of the Žitný ostrov island, and the Danubian Hills in the north, centre and east. Mountain ranges reaching into the region are: Považský Inovec in the north-west, where the region's highest point, Veľký Inovec, is located, Tribeč in the north from Nitra, Pohronský Inovec in the north-east and Štiavnické vrchy in the east. Major rivers are the Danube in the south, Váh in the south-west, Nitra in the western-central part, Hron in the east and Ipeľ in the south-east. As for administrative divisions, the region borders Trenčín Region in the north, Banská Bystrica Region in the east, Hungarian Pest in the south-east, Komárom-Esztergom in the south, and Győr-Moson-Sopron county in the south-west and Trnava Region in the west.

Demographics.

The population density in the region is 113 inhabitants per km2, which is very similar to the country's average (110 per km2). The largest towns are Nitra, Komárno, Nové Zámky and Levice. According to the 2001 census, there were 713,422 inhabitants in the region, with a majority of Slovaks (68.3%), but there is a numerous Hungarian minority (27.6%) in the southern districts, forming a majority in the Komárno District (72%) and there are small minorities of Czechs and Roma (<1%).

Economy and climate.

The city of Nitra is also the centre of whole region. The region - which is the warmest in Slovakia - reaches a high production of wheat, rye and vegetables. Significant industries are: the food industry, with breweries in Topoľčany, Nitra and Hurbanovo, are machinery (fridges in Zlaté Moravce, shipyards in Komárno) and energy (Mochovce Nuclear Power Plant).

Administrative division.

The Nitra Region consists of 7 districts.  There are 350 municipalities, of which 16 are towns (in bold).

The Nitra Region (, ; ) is one of the administrative regions of Slovakia. It was first established in 1923 and from 1996 exists in its present borders. It consists of seven districts () and 354 municipalities, from which 16 have a town status. The economy of the region focuses more on agriculture, than in other Slovak regions. Nitra is its seat, largest city, and cultural and economic center.

Nitranský kraj (slovensky Nitriansky kraj), s hlavním městem Nitrou, je jeden z krajů Slovenska. Před rokem 1990 patřilo celé území Nitranského kraje ke kraji Západoslovenskému. Má 686 662 obyvatel (2013).


Early life.

Wenders was born in Düsseldorf, Germany, into a traditionally Catholic family. His father, Heinrich Wenders, was a surgeon. The Dutch name "Wim" is a shortened version of the baptismal name "Wilhelm". As a boy, he took unaccompanied trips to Amsterdam to visit the Rijksmuseum. He graduated from high school in Oberhausen in the Ruhr area. He then studied medicine (1963–64) and philosophy (1964–65) in Freiburg and Düsseldorf, but dropped out of school and moved to Paris in October 1966 to become a painter. Wenders failed his entry test at France's national film school, IDHEC (now La Fémis), and instead became an engraver at Johnny Friedlaender's studio in Montparnasse. During this time, Wenders became fascinated with cinema, and saw up to five movies a day at the local movie theater.  Set on making his obsession also his life's work, Wenders returned to Germany in 1967 to work in the Düsseldorf office of United Artists. That fall, he entered the Hochschule für Fernsehen und Film München (University of Television and Film Munich). Between 1967 and 1970, while at the "HFF", Wenders also worked as a film critic for "FilmKritik", the Munich daily newspaper "Süddeutsche Zeitung", "Twen" magazine, and "Der Spiegel".  Wenders completed several short films before graduating from the Hochschule with a feature-length 16mm black-and-white film, "Summer in the City" (1970).

Career.

Wenders began his career during the New German Cinema era of the late 1960s, making his feature directorial debut with "Summer in the City" (1970). Much of the distinctive cinematography in his movies is the result of a highly productive long-term collaboration with Dutch cinematographer Robby Müller. Some of his more successful and critically acclaimed movies—"Paris, Texas" and "Wings of Desire", for example—have been the result of fruitful collaborations with "avant-garde" authors Peter Handke and Sam Shepard. Handke's novel "The Goalie's Anxiety at the Penalty Kick" was adapted for Wenders's second feature film, "The Goalkeeper's Fear of the Penalty." Handke co-wrote the script for "Wings of Desire" and "Until the end of the World", both featuring Solveig Dommartin. Wenders has directed several highly acclaimed documentaries, most notably "Buena Vista Social Club" (1999), about Cuban musicians, and "The Soul of a Man" (2003), on American blues. He has also directed a documentary style film on the Skladanowsky brothers, known in English as "A Trick of the Light". The Skladanowsky brothers were inventing'moving pictures' when several others like the Lumière brothers and William Friese-Greene were doing the same. Alongside "Buena Vista Social Club" his documentaries on Pina Bausch, "Pina", and Sebastiao Salgado, "The Salt of the Earth" also received nominations for the Academy Award for Best Documentary Feature.  Wenders has also directed many music videos for groups such as U2 and Talking Heads, including "Stay (Faraway, So Close!)" and "Sax and Violins". His television commercials include a UK advertisement for Carling Premier Canadian beer. Wenders's book "Emotion Pictures", a collection of diary essays written as a film student, was adapted and broadcast as a series of plays on BBC Radio 3, featuring Peter Capaldi as Wenders, with Gina McKee, Saskia Reeves, Dennis Hopper, Harry Dean Stanton and Ricky Tomlinson, dramatised by Neil Cargill.  Wenders was collaborating with artist/journalist and longtime friend Melinda Camber Porter on a documentary feature about his body of work, "Wim Wenders – Visions on Film", when Porter died. The film remains incomplete.  Wenders is a member of the advisory board of World Cinema Foundation. The project was founded by Martin Scorsese and aims to find and reconstruct world cinema films that have been neglected. He serves as a Jury Member for the digital studio Filmaka, a platform for undiscovered filmmakers to show their work to industry professionals. In 2011 he was selected to stage the 2013 cycle of Richard Wagner's "Der Ring des Nibelungen" at the Bayreuth Festival. The project fell through when he insisted on filming in 3-D, which the Wagner family found too costly and disruptive.  While promoting his 3-D dance film, "Pina", Wenders told the Blog in December 2011 that he had begun work on a new 3-D documentary about architecture. He also said he would only work in 3-D from then on. Wenders had admired the dance choreographer Pina Bausch since 1985, but only with the advent of digital 3-D cinema did he decide that he could sufficiently capture her work on screen.  He stage-directed Georges Bizet's opera "Les Pêcheurs de perles", starring Olga Peretyatko and Francesco Demuro and conducted by Daniel Barenboim at the Berlin State Opera in June 2017 (Staatsoper).  In a 2018 interview, Wenders said his favorite movie of all time was his film about Pope Francis, and that his entire career had been building up to it. His admiration for Francis is profound; he said he felt the Pope is doing his best in a difficult time, in a world full of calamities. He also said that, though raised Catholic, he had converted to Protestantism years before.

Photography.

Alongside filmmaking, Wim Wenders works with the medium of photography and his poignant images of desolate landscapes engage themes including memory, time, loss, nostalgia and movement. Wenders' long-running artistic project, "Pictures from the Surface of the Earth", began in the early 1980s and was subsequently pursued by the artist for the next twenty years. The initial photographic series in this body of work was titled "Written in the West" which Wenders produced when criss-crossing through the American West in preparation for his film "Paris, Texas" (1984). This became the starting point for the artist's nomadic journey across the globe, travelling through countries including Germany, Australia, Cuba, Israel and Japan to take photographs which capture the essence of a moment, place or space.

Selected exhibitions.

2016.

"The Space Between the Characters Can Carry the Load", Collection Ivo Wessel, Weserburg Museum for modern Art, Bremen, DE

Legacy and honors.

Wenders has received many awards, including the Golden Lion for "The State of Things" at the Venice Film Festival (1982); the Palme d'Or at the 1984 Cannes Film Festival for his movie "Paris, Texas"; and Best Direction for "Wings of Desire" in the 1987 Bavarian Film Awards and the 1987 Cannes Film Festival. In 1993 he won the Bavarian Film Awards for Best Director for "Faraway, So Close!". In 2004, he received the Master of Cinema Award of the International Filmfestival Mannheim-Heidelberg. He was awarded the Leopard of Honour at the Locarno International Film Festival in 2005. In 2012, his dance film "Pina" was nominated for the Best Documentary Feature of the 84th Academy Awards. Wenders also received a nomination for the Writers Guild of America Award for Best Documentary Screenplay for the film.  He has been awarded honorary doctorates by the Sorbonne in Paris in 1989, the University of Fribourg (Switzerland) in 1995 and the Université Catholique de Louvain, Belgium in 2005.  In 2012 the Wim Wenders Foundation was established in Düsseldorf. The foundation provides a framework to bring together his cinematic, photographic, artistic and literary works in his native country and to make it permanently accessible to the public.  Wenders was awarded the Honorary Golden Bear at the 65th Berlin International Film Festival in February 2015. In 2016, Wenders received the Großer Kulturpreis of the Sparkassen Culture-Foundation Rhineland, one of the highest endowed cultural honorings in Germany, with previous winners such as photographer legend Hilla Becher, sculptor Tony Cragg, musician Wolfgang Niedecken and director Sönke Wortmann. In 2017, Wenders received the Douglas Sirk Award at the Hamburg Film Festival.

Personal life.

Wenders has lived in Berlin since the mid-1970s. He is an ecumenical Christian; he wished to become a Catholic priest during his teenage years.

Ernst Wilhelm "Wim" Wenders (; born 14 August 1945) is a German filmmaker, playwright, author, and photographer. He is a major figure in New German Cinema. Among many honors, he has received three nominations for the Academy Award for Best Documentary Feature: for "Buena Vista Social Club" (1999), about Cuban music culture; "Pina" (2011), about the contemporary dance choreographer Pina Bausch; and "The Salt of the Earth" (2014), about Brazilian photographer Sebastião Salgado.

Wim Wenders, vlastním jménem Ernst Wilhelm Wenders, (* 14. srpna 1945 v Düsseldorfu) je německý filmový režisér, fotograf a producent.


Indexed color.

With the relatively low color depth, the stored value is typically a number representing the index into a color map or palette (a form of vector quantization). The colors available in the palette itself may be fixed by the hardware or modifiable by software. Modifiable palettes are sometimes referred to as pseudocolor palettes.  Old graphics chips, particularly those used in home computers and video game consoles, often have the ability to use a different palette per sprites and tiles in order to increase the maximum number of simultaneously displayed colors, while minimizing use of then-expensive memory (and bandwidth). For example, in the ZX Spectrum the picture is stored in a two-color format, but these two colors can be separately defined for each rectangular block of 8×8 pixels.  The palette itself has a color depth (number of bits per entry). While the best VGA systems only offered an 18-bit (262,144 color) palette from which colors could be chosen, all color Macintosh video hardware offered a 24-bit (16 million color) palette. 24-bit palettes are pretty much universal on any recent hardware or file format using them.  If instead the color can be directly figured out from the pixel values, it is "direct color". Palettes were rarely used for depths greater than 12 bits per pixel, as the memory consumed by the palette would exceed the necessary memory for direct color on every pixel.

List of common depths.

1-bit color.

2 colors, often black and white (or whatever color the CRT phosphor was) direct color. Sometimes 1 meant black and 0 meant white, the inverse of modern standards. Most of the first graphics displays were of this type, the X window system was developed for such displays, and this was assumed for a 3M computer. The first Macintoshes, Atari ST high resolution. In the late 80's there were professional displays with resolutions up to 300dpi (the same as a contemporary laser printer) but color proved more popular.

2-bit color.

4 colors, usually from a selection of fixed palettes. The CGA, gray-scale early NeXTstation, color Macintoshes, Atari ST medium resolution.

3-bit color.

8 colors, almost always all combinations of full-intensity red, green, and blue. Many early home computers with TV displays, including the ZX Spectrum and BBC Micro.

4-bit color.

16 colors, usually from a selection of fixed palettes. Used by the EGA and by the least common denominator VGA standard at higher resolution, color Macintoshes, Atari ST low resolution, Commodore 64, Amstrad CPC.

5-bit color.

32 colors from a programmable palette, used by the Original Amiga chipset.

8-bit color.

256 colors, usually from a fully-programmable palette. Most early color Unix workstations, VGA at low resolution, Super VGA, color Macintoshes, Atari TT, Amiga AGA chipset, Falcon030, Acorn Archimedes. Both X and Windows provided elaborate systems to try to allow each program to select its own palette, often resulting in incorrect colors in any window other than the one with focus.  Some systems placed a color cube in the palette for a direct-color system (and so all programs would use the same palette). Usually fewer levels of blue were provided than others, as the normal human eye is less sensitive to the blue component than to the red or green (two thirds of the eye's receptors process the longer wavelengths) Popular sizes were:

12-bit color.

4096 colors, usually from a fully-programmable palette (though it was often set to a 16×16×16 color cube). Some Silicon Graphics systems, Color NeXTstation systems, and Amiga systems in HAM mode.

High color (15/16-bit).

In high-color systems, two bytes (16 bits) are stored for each pixel. Most often, each component (R, G, and B) is assigned five bits, plus one unused bit (or used for a mask channel or to switch to indexed color); this allows 32,768 colors to be represented. However, an alternate assignment which reassigns the unused bit to the G channel allows 65,536 colors to be represented, but without transparency. These color depths are sometimes used in small devices with a color display, such as mobile phones, and are sometimes considered sufficient to display photographic images. Occasionally 4 bits per color are used plus 4 bits for alpha, giving 4096 colors.  The term "high color" has recently been used to mean color depths greater than 24 bits.

18-bit.

Almost all of the least expensive LCDs (such as typical twisted nematic types) provide 18-bit color (64×64×64 = 262,144 combinations) to achieve faster color transition times, and use either dithering or frame rate control to approximate 24-bit-per-pixel true color, or throw away 6 bits of color information entirely. More expensive LCDs (typically IPS) can display 24-bit color depth or greater.

True color (24-bit).

24 bits almost always use 8 bits each of R, G, and B. As of 2018, 24-bit color depth is used by virtually every computer and phone display and the vast majority of image storage formats. Almost all cases of 32 bits per pixel assigns 24 bits to the color, and the remaining 8 are the alpha channel or unused.  2 gives 16,777,216 color variations. The human eye can discriminate up to ten million colors and since the gamut of a display is smaller than the range of human vision, this means this should cover that range with more detail than can be perceived. However, displays do not evenly distribute the colors in human perception space, so humans can see the changes between some adjacent colors as color banding. Monochromatic images set all three channels to the same value, resulting in only 256 different colors and thus, potentially, more visible banding, as the average human eye can only distinguish between about 30 shades of gray. Some software attempts to dither the gray level into the color channels to increase this, although in modern software this is more often used for subpixel rendering to increase the space resolution on LCD screens where the colors have slightly different positions.  The DVD-Video and Blu-ray Disc standards support a bit depth of 8 bits per color in YCbCr with 4:2:0 chroma subsampling. YCbCr can be losslessly converted to RGB.  Macintosh systems refer to 24-bit color as "millions of colors". The term "true color" is sometimes used to mean what this article is calling "direct color". It is also often used to refer to all color depths greater or equal to 24.

Deep color (30-bit).

"Deep color" consists of a billion or more colors. 2 is approximately 1.073 billion. Usually this is 10 bits each of red, green, and blue. If an alpha channel of the same size is added then each pixel takes 40 bits.  Some earlier systems placed three 10-bit channels in a 32-bit word, with 2 bits unused (or used as a 4-level alpha channel); the Cineon file format, for example, used this. Some SGI systems had 10- (or more) bit digital-to-analog converters for the video signal and could be set up to interpret data stored this way for display. BMP files define this as one of its formats, and it is called "HiColor" by Microsoft.  Video cards with 10 bits per component started coming to market in the late 1990s. An early example was the Radius ThunderPower card for the Macintosh, which included extensions for QuickDraw and Adobe Photoshop plugins to support editing 30-bit images. Some vendors call their 24-bit color depth with FRC panels 30-bit panels; however, true deep color displays have 10-bit or more color depth without FRC.  The HDMI 1.3 specification defines a bit depth of 30 bits (as well as 36 and 48 bit depths). In that regard, the Nvidia Quadro graphics cards manufactured after 2006 support 30-bit deep color and Pascal or later GeForce and Titan cards when paired with the Studio Driver as do some models of the Radeon HD 5900 series such as the HD 5970. The ATI FireGL V7350 graphics card supports 40- and 64-bit pixels (30 and 48 bit color depth with an alpha channel).  The DisplayPort specification also supports color depths greater than 24 bpp in version 1.3 through "VESA Display Stream Compression, which uses a visually lossless low-latency algorithm based on predictive DPCM and YCoCg-R color space and allows increased resolutions and color depths and reduced power consumption."  At WinHEC 2008, Microsoft announced that color depths of 30 bits and 48 bits would be supported in Windows 7, along with the wide color gamut scRGB.  High Efficiency Video Coding (HEVC or H.265) defines the Main 10 profile, which allows for 8 or 10 bits per sample with 4:2:0 chroma subsampling. The Main 10 profile was added at the October 2012 HEVC meeting based on proposal JCTVC-K0109 which proposed that a 10-bit profile be added to HEVC for consumer applications. The proposal stated that this was to allow for improved video quality and to support the Rec. 2020 color space that will be used by UHDTV. The second version of HEVC has five profiles that allow for a bit depth of 8 bits to 16 bits per sample.  A few smartphones use 30-bit color depth, namely the OnePlus 8 Pro, the Oppo Find X2 & Find X2 Pro, the Sony Xperia 1 II and the Sharp Aquos Zero 2.

36-bit.

Using 12 bits per color channel produces 36 bits, approximately 68.71 billion colors. If an alpha channel of the same size is added then there are 48 bits per pixel.

48-bit.

Using 16 bits per color channel produces 48 bits, approximately 281.5 trillion colors. If an alpha channel of the same size is added then there are 64 bits per pixel.  Image editing software such as Photoshop started using 16 bits per channel fairly early in order to reduce the quantization on intermediate results (i.e. if an operation is divided by 4 and then multiplied by 4, it would lose the bottom 2 bits of 8-bit data, but if 16 bits were used it would lose none of the 8-bit data). In addition, digital cameras were able to produce 10 or 12 bits per channel in their raw data; as 16 bits is the smallest addressable unit larger than that, using it would allow the raw data to be manipulated. These systems did not take advantage of 16 bits for high dynamic range, and some assign almost mystical capabilities to 16 bits that are not actually true.

High dynamic range and wide gamut.

Some systems started using those bits for numbers outside the 0–1 range rather than for increasing the resolution. Numbers greater than 1 were for colors brighter than the display could show, as in high-dynamic-range imaging (HDRI). Negative numbers can increase the gamut to cover all possible colors, and for storing the results of filtering operations with negative filter coefficients. The Pixar Image Computer used 12 bits to store numbers in the range [-1.5,2.5), with 2 bits for the integer portion and 10 for the fraction. The Cineon imaging system used 10-bit professional video displays with the video hardware adjusted so that a value of 95 was black and 685 was white. The amplified signal tended to reduce the lifetime of the CRT.

Linear color space and floating point.

More bits also encouraged the storage of light as linear values, where the number directly corresponds to the amount of light emitted. Linear levels makes calculation of light (in the context of computer graphics) much easier. However, linear color results in disproportionately more samples near white and fewer near black, so the quality of 16-bit linear is about equal to 12-bit sRGB.  Floating point numbers can represent linear light levels spacing the samples semi-logarithmically. Floating point representations also allow for drastically larger dynamic ranges as well as negative values. Most systems first supported 32-bit per channel single-precision, which far exceeded the accuracy required for most applications. In 1999, Industrial Light & Magic released the open standard image file format OpenEXR which supported 16-bit-per-channel half-precision floating-point numbers. At values near 1.0, half precision floating point values have only the precision of an 11-bit integer value, leading some graphics professionals to reject half-precision in situations where the extended dynamic range is not needed.

More than three primaries.

Virtually all television displays and computer displays form images by varying the strength of just three primary colors: red, green, and blue. For example, bright yellow is formed by roughly equal red and green contributions, with no blue contribution.  Additional color primaries can widen the color gamut of a display, since it is no longer limited to the shape of a triangle in the CIE 1931 color space. Recent technologies such as Texas Instruments's "BrilliantColor" augment the typical red, green, and blue channels with up to three other primaries: cyan, magenta and yellow. Mitsubishi and Samsung, among others, use this technology in some TV sets to extend the range of displayable colors. The Sharp Aquos line of televisions has introduced Quattron technology, which augments the usual RGB pixel components with a yellow subpixel. However, formats and media supporting these extended color primaries are extremely uncommon.  For storing and working on images, it is possible to use "imaginary" primary colors that are not physically possible so that the triangle does enclose a much larger gamut, so whether more than three primaries results in a difference to the human eye is not yet proven, since humans are primarily trichromats, though tetrachromats exist.

Color depth or colour depth (see spelling differences), also known as bit depth, is either the number of bits used to indicate the color of a single pixel, in a bitmapped image or video framebuffer, or the number of bits used for each color component of a single pixel. For consumer video standards, such as High Efficiency Video Coding (H.265), the bit depth specifies the number of bits used for each color component. When referring to a pixel, the concept can be defined as bits per pixel (bpp), which specifies the number of bits used. When referring to a color component, the concept can be defined as bits per component, bits per channel, bits per color (all three abbreviated bpc), and also bits per pixel component, bits per color channel or bits per sample (bps). Color depth is only one aspect of color representation, expressing the precision with which colors can be expressed; the other aspect is how broad a range of colors can be expressed (the gamut). The definition of both color precision and gamut is accomplished with a color encoding specification which assigns a digital code value to a location in a color space.

Barevná hloubka je termín používaný v počítačové grafice, který popisuje počet bitů použitých k popisu určité barvy pixelu v bitmapovém obrázku nebo rámečku videa. Toto pojetí je také známé jako počet bitů na pixel, zejména je-li uvedeno spolu s počtem použitých pixelů. Větší barevná hloubka zvětšuje škálu různých barev a přirozeně také paměťovou náročnost obrázku či videa.


History.

Ancient Greek period.

"Bouthroton" (modern day Butrint) was originally one of the major centres of the Epirote tribe of the Chaonians, part of the northwestern Greek group of tribes. They had close contacts to the Corinthian colony of Corcyra (modern Corfu). According to the Roman writer Virgil, its legendary founder was the seer Helenus, a son of king Priam of Troy, who had moved West after the fall of Troy with Neoptolemus and his concubine Andromache. Both Virgil and the Greek historian Dionysius of Halicarnassus recorded that Aeneas visited "Bouthroton" after his own escape from the destruction of Troy.  The earliest archaeological evidence of settled occupation dates to between 10th and 8th centuries BC, although some claim that there is earlier evidence of habitation dating from the 12th century BC.  Excavation at Bouthroton has yielded Proto-Corinthian pottery of the 7th century and then Corinthian and Attic pottery of the 6th century, however there are no indications of a prehistoric settlement. "Bouthroton" was in a strategically important position due its access to the Straits of Corfu, and its location at the crossroads of mainland Greece and Magna Graecia, the Greek and the "barbarian" worlds. Thus, it became one of the two ancient ports in lower Chaonia, the other being Onchesmos (modern Sarandë).  The acropolis was erected on a hill on the bank of a lake Butrint (or lake Bouthrotum). The first extension of the 7th century BC acropolis occurred during the 5th century BC. During the first years of the second Peloponnesian War (413-404 BC) the Corkyreans built fortifications stretching from Ksamil to Buthrotum. Buthrotum being previously an independent city, became subject to nearby Corfu.  By the 4th century BC it had grown in importance and included a theatre, a sanctuary dedicated to Asclepius and an agora. The acropolis of Bouthrotum was protected by three circuit walls. The last and outer wall was erected around 380 BC enclosing and area of 4ha. This 870m-long wall included bastions and five gates. Two of the most important gates were known as Scean and Lion gate. Moreover, the agora, the stoas, the residential zone and the theatre were located in a separate walled area.  Several inscriptions in Buthrotum describe the organization of the Chaonians in the beginning of the 3rd cent. BC. which show that they too had an annual leader called "Prostates" ( Protector). The Greek calendar of Bouthroton appears in the oldest known computer, the so-called Antikythera Mechanism (c. 150 to 100 BC).  The theatre is known for the impressive number of inscriptions carved on its stones. Most of them deal with manumissions and give a great amount of details on the city during the Hellenistic era. The names of those slaves were almost exclusively Greek with a few exception of Latin ones which bore Greek family names.  In 228 BC "Buthrotum" became a Roman protectorate alongside Corfu. In the middle of the second century BC Buthrotum was the centre of an independent state, possibly the "Koinon of the Prasaiboi", as listed in the list of the theorodokoi at the Oracle of Delphi.

Ancient Roman period.

In the next century, it became a part of a province of Macedonia. In 44 BC, Caesar designated "Buthrotum" as a colony to reward soldiers who had fought for him against Pompey. Local landholder Titus Pomponius Atticus objected to his correspondent Cicero who lobbied against the plan in the Senate. As a result, only small numbers of colonists were settled. In 31 BC, Roman Emperor Augustus fresh from his victory over Mark Antony and Cleopatra at the battle of Actium renewed the plan to make "Buthrotum" a veterans' colony. New residents expanded the city and the construction included an aqueduct, a Roman bath, houses, a forum complex and a nymphaeum. During that era the size of the town was doubled. A number of new structures were built next to the existing ones especially around the theatre and the temple of Asklepeios.  In the 3rd century AD, an earthquake destroyed a large part of the town, levelling buildings in the suburbs on the Vrina Plain and in the forum of the city centre. Excavations have revealed that city had already been in decline. However, the settlement survived into the late antique era, becoming a major port in the province of Old Epirus. The town of late antiquity included the grand "Triconch Palace", the house of a major local notable that was built around 425.

Byzantine and Slavic period.

The walls of the city were extensively rebuilt, most probably at the end of the 5th century, perhaps by Byzantine Emperor Anastasius. The Ostrogoths under Indulf raided the Ionian coast in 550 and may have attacked Buthrotum. In the end of 6th century groups of Slavs possibly arrived at Buthrotum. Evidence from the excavations shows that importation of commodities, wine and oil from the Eastern Mediterranean continued into the early years of the 7th century when the early Byzantine Empire lost these provinces. During the period of Slavic invasions and population movements in the wider region Butrotum was one of the few cities in Epirus that survived and retained its status as a seat of a bishopric without interruption. Because of the scarcity of sources, it is difficult to assess whether Buthrotum was controlled by Slavs or Byzantines between the 7th to 10th centuries.  The Grand Basilica of Buthrotum was built during the first half of the 6th century on the northeast side of the settlement. Other monuments include the Acropolic Basilica (4th century), the Triconch Palace (6th century), the Baptistery with a large, complex mosaic (6th century), the Lake Gate church (9th century) and the Baptistery church (9th century). Arab traveller Muhammad al-Idrisi noted in the 12th century that Buthrotum is a densely populated city with a number of markets.  It remained an outpost of the Byzantine empire fending off assaults from the Normans until 1204 when following the Fourth Crusade, the Byzantine Empire fragmented, Buthrotum falling to the breakaway Despotate of Epirus. In the following centuries, the area was a site of conflict between the Byzantines, the Angevins of southern Italy, and the Venetians.

Between Angevins, Byzantine Empire and Despotate of Epirus.

The fortifications were probably strengthened by Byzantine Emperor Michael I.  In 1267, Charles of Anjou took control of both Buthrotum and Corfu, leading to further restorations of the walls and the Grand Basilica. In 1274, Byzantine forces re-entered Buthrotum, an act which caused conflict between the Byzantines and the Despotate of Epirus, because Despot Nikephoros considered the site to be his domain. Despite deep religious differences between the Catholic Charles of Anjou and the staunchly Orthodox Nikephoros, the two allied against Byzantine Emperor Michael, and together drove the Byzantines from the area in 1278. Then, pressed by Charles, Nikephoros ultimately ended up recognizing Charles' rights to all the town that Michael II had awarded to Manfred of Hohenstaufen as part of his wife Helen's dowr, as Charles was his successor, thus ceding to him Buthrotum as well as the entire Acroceraunian Coast from Vlora to Buthrotum.

As part of the Angevin "Regnum Albaniae".

Buthrotum remained under Angevin rule until 1386, with only two other interruptions: in 1306, and in 1313–1331. In 1305-1306 it was controlled by the Despot of Epirus, Thomas I Komnenos Doukas. Buthrotum became Catholic after it was conquered by the Angevins, and remained so throughout the fourteenth century.  Hodges argues that the "episodic" defensive investment in Buthrotum as a town during this period demonstrates that it still possessed an active urban population, although not one urban dwelling had been identified at the time of writing. Hodges argues this indicates that dwellings were concentrated on the slopes of the northern citadel. The Orthodox Bishopric was transferred to nearby Glyki in 1337 or 1338. The town was reduced in size during the end of the 14th century, due to the tumultuous unrest in the region.

Between Venice and the Ottoman Empire.

The dogal Republic of Venice purchased the area including Corfu from the Angevins in 1386; however, the Venetian merchants were principally interested in Corfu and Buthrotum once again declined.  By 1572 the wars between Venice and the Ottoman Empire had left Buthrotum ruinous and the acropolis was abandoned, while at the order of Domenico Foscarini, the Venetian commander of Corfu, the administration of Buthrotum and its environs was shifted to a small triangular fortress associated with the extensive fish weirs. The area was lightly settled afterwards, occasionally being seized by the Ottoman Turks, in 1655 and 1718, before being recaptured by the Venetians. Its fisheries were a vital contributor to the supply of Corfu, and olive growing together with cattle and timber were the principal economic activities.  The Treaty of Campo Formio of 1797 split between France and Austria the territory of the Republic of Venice, which France had just occupied and abolished, and under article 5 of the treaty, Butrinto and the other former Venetian enclaves in Albania came under French sovereignty. However, in 1799, the local Ottoman governor Ali Pasha Tepelena conquered it, and it became a part of the Ottoman Empire until Albania gained its independence in 1913. By that time, the site of the original city had been unoccupied for centuries and was surrounded by malarial marshes.

Modern Albania.

In 1913, after the end of the First Balkan War, Butrint was ceded to Greece but Italy challenged the decision and in the Treaty of London the region was given to the newly created Albania. As such Butrint was located near the southern border of the newly established Albanian state in a largely Greek-speaking terriroty. The local Greek population was enraged and created an Autonomous Republic of Northern Epirus, for six months, before it was reluctantly ceded to Albania, with peace assured by Italian peacekeeping force until 1919. Italy rejected the decision because she didn't want Greece to control both sides of the Straits of Corfu.

Ecclesiastical history.

Residential bishopric.

In the early 6th century, Buthrotum became the seat of a bishopric and new construction included the Buthrotum baptistery, one of the largest such paleochristian buildings of its type, and a basilica. The diocese of Buthrotum was initially a suffragan of the Metropolis of Nicopolis, the metropolitan capital of Epirus Vetus and in the papal sway, but in the 9th and 10th centuries it is listed with the suffragans of Naupaktos, which succeeded ruined Nicopolis as provincial capital and metropolis of the new Byzantine theme of Nicopolis, bringing it in the sway of the Byzantine Patriarchate of Constantinople. After the 14th century, it was under the jurisdiction of the Metropolis of Ioannina. Two of its Byzantine (pre-Eastern Schism) bishops are mentioned in extant documents:

Latin residential bishopric.

A Latin see was established circa 1250 under the Italian name "Butrinto", functioning under Angevin and Venetian rule, but suppressed circa 1400. The 6th-century basilica was rebuilt by king Charles I of Naples in 1267.

Catholic titular see.

Buthrotum is today listed by the Catholic Church as a Latin titular see since the diocese was nominally restored in 1933 as titular bishopric of Buthrotum (Latin) / Butrinto (Curiate Italian) / Butrint (Albanian).  Following titular bishops have been nominated:

Archaeological excavations.

The first modern archaeological excavations began in 1928 when the Fascist government of Benito Mussolini's Italy sent an expedition to Butrint. The aim was geopolitical rather than scientific, aiming to extend Italian hegemony in the area. The leader was an Italian archaeologist, Luigi Maria Ugolini who despite the political aims of his mission was a good archaeologist. Ugolini died in 1936, but the excavations continued until 1943 and the Second World War. They uncovered the Hellenistic and Roman part of the city including the "Lion Gate" and the "Scaean Gate" (named by Ugolini for the famous gate at Troy mentioned in the Homeric "Iliad").  After the communist government of Enver Hoxha took Albania over in 1944, foreign archaeological missions were banned. Albanian archaeologists including Hasan Ceka continued the work. Nikita Khrushchev visited the ruins in 1959 and suggested that Hoxha should turn the area into a submarine base. The Albanian Institute of Archaeology began larger scale excavations in the 1970s. Since 1993 further major excavations have taken place led by the Butrint Foundation in collaboration with the Albanian Institute of Archaeology. Recent excavations in the western defences of the city have revealed evidence of the continued use of the walls, implying the continuation of life in the town. The walls themselves certainly seem to have burnt down in the 9th century, but were subsequently repaired.  After the collapse of the communist regime in 1992, the new democratic government planned various major developments at the site. The same year remains of Butrint were included in the UNESCO list of World Heritage Sites. A major political and economic crisis in 1997 and lobbying stopped the airport plan and UNESCO placed it on the List of World Heritage in Danger because of looting, lack of protection, management and conservation. Archaeological missions during 1994–9 uncovered further Roman villas and an early Christian church.

Directions.

The site of Butrint is accessible from Sarandë, along a road first built in 1959 for a visit by the Soviet leader Nikita Khrushchev. This road was upgraded during the summer of 2010. The construction was somewhat of an environmental disaster and may yet threaten Butrint's World Heritage Site status. The ancient city is becoming a popular tourist destination, attracting day-trippers from the nearby Greek holiday island of Corfu. Hydrofoils (30 minutes) and ferries (90 minutes) run daily between the New Port in Corfu Town and Saranda. Many visitors from Corfu use chartered coach services to visit Butrint from Sarandë, and additionally, a regular public bus service runs between Sarandë port and Butrint. Others arrive from the Qafe Bote border crossing with Greece near Konispol and cross the Vivari Channel by the cable ferry at Butrint.

Butrint (; from ) was an Greek and later Roman city and bishopric in Epirus. Perhaps inhabited since prehistoric times, Buthrotum was a city of the Epirote tribe of the Chaonians, later a Roman colony and a bishopric. It entered into decline in Late Antiquity, before being abandoned during the Middle Ages after a major earthquake flooded most of the city. In modern times it is an archeological site in Vlorë County, Albania, some 14 kilometres south of Sarandë and close to the Greek border. It is located on a hill overlooking the Vivari Channel and is part of the Butrint National Park. Today Bouthrotum is a Latin Catholic titular see and also features the Ali Pasha Castle.

Historické město Butrint se nachází na samém jihu Albánie při hranicích s Řeckem na jihovýchodním výběžku poloostrova Ksamili, který odděluje Kerkyrský průliv Jónského moře od Butrintského jezera a Vivarského kanálu. Vzhledem ke své strategické poloze ve Středozemním moři bylo město svědkem vojenských operací od Peloponéské války v 5. století př. n. l. až po napoleonské války v 19. století. Původně byl osídlen řeckým kmenem Achájů. Ve 4. století př. n. l. jej obsadili kolonisté z "Kerkyry" (Korfu) a stal se významným opevněným přístavem a obchodním centrem s vlastní akropolí. Poté jej ovládli Illyrové a v průběhu 2. makedonské války byl roku 167 př. n. l. dobyt Římany. I po vytvoření Byzantské říše zůstal v rukou Římanů a to až do tureckého vpádu v roce 1453.