Japanese input methods
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Japanese input methods are the methods used to input Japanese characters on a computer.
There are two main methods of inputting Japanese on computers. One is via a romanized version of Japanese called rōmaji (literally "Roman letters"), and the other is via keyboard keys corresponding to the Japanese kana. Some systems may also work via a graphical user interface, or GUI, where the characters are chosen by clicking on buttons or image maps.
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[edit] Japanese keyboards
Japanese keyboards have both kana and Roman letters indicated. The JIS, or Japanese Industrial Standard, keyboard layout keeps the Roman letters in the usual qwerty layout, with numbers above them. Many of the non-alphanumeric symbols are the same as on English-language keyboards, but some symbols are located in other places.
The kana symbols are also ordered in a consistent way across different keyboards. For example, the Q W E R T Y keys correspond to た て い す か ん (Ta Te I Su Ka N') when the computer is used for direct kana input.
Keyboards with kana markings are rarely found outside of Japan (but occasionally found in Hong Kong); however, there is no special hardware requirement for a user to input Japanese via the romaji input method. Most newer operating systems allow this function, even when the operating system itself is in English or another non-Japanese language, and a non-Japanese keyboard is used.
[edit] Input keys
Since Japanese input requires switching between Roman and kana entry modes, and also conversion between kana and kanji (as discussed below), there are usually several special keys on the keyboard. This varies from computer to computer, and some OS vendors have striven to provide a consistent user interface regardless of the type of keyboard being used. On non-Japanese keyboards, option- or control- key sequences can do all of the tasks mentioned below.
On most Japanese keyboards, one key switches between Roman characters and Japanese characters. Sometimes, each mode (Roman, and Japanese) may even have its own key, in order to prevent ambiguity when the user is typing quickly.
There may also be a key to instruct the computer to convert the latest kana characters into kanji, although usually the space key serves the same purpose since Japanese writing is devoid of spaces.
Some keyboards have a mode key to switch from the different types of kana being entered. Hiragana, katakana, halfwidth katakana, halfwidth Roman letters, and fullwidth Roman letters are some of the options. A typical Japanese character is square while Roman characters are typically variable in width. Since all Japanese characters occupy the space of a square box, it is sometimes desirable to input Roman characters in the same square form in order to preserve the grid layout of the text. These Roman characters that have been fitted to a square character cell are called fullwidth, while the normal ones are called halfwidth. In some fonts these are fitted to half-squares, like some monospaced fonts, while in others they are not. Often, fonts are available in two variant, one with the halfwidth characters monospaced, and another one with proportional halfwidth characters. The name of the typeface with proportional halfwidth characters is often prefixed with "P" for "proportional".
Finally, a keyboard may have a special key to tell the OS that the last kana entered should not be converted to kanji. Sometimes this is just the Return/Enter key.
[edit] Mobile phones
The system used to input Japanese on mobile phones is based on the numerical keypad. Each number is associated with a particular sequence of kana, such as ka, ki, ku, ke, ko for '2', and the button is pressed repeatedly to get the correct kana. Dakuten and handakuten marks, punctuation, and other symbols can be added by other buttons in the same way. Kana to kanji conversion is done via the arrow and other keys.
[edit] Other
Other consumer devices in Japan which allow for text entry via on-screen programming, such as digital video recorders and the Nintendo Wii, allow the user to toggle between the numerical keypad and a full keyboard (QWERTY, or ABC order) input system.
[edit] Kana to kanji conversion
After the kana have been input, they are either left as they are, or converted into kanji. The Japanese language has many homonyms, and conversion of a kana spelling (representing the pronunciation) into a kanji (representing the meaning of the word) is often a one-to-many process. The kana to kanji converter offers a list of candidate kanji writings for the input kana, and the user may use the space bar or arrow keys to scroll through the list of candidates until he or she reaches the correct writing. On reaching the correct written form, pressing the Enter key, or sometimes the "henkan" key, ends the conversion process. This selection can also be controlled through the GUI with a mouse or other pointer device.
If the hiragana is required, pressing the Enter key immediately after the characters are entered will end the conversion process and results in the hiragana as typed. If katakana is required, it is usually presented as an option along with the kanji choices. Alternatively, on some keyboards, pressing the muhenkan (無変換?) (literally "no conversion") button switches between katakana or hiragana.
Sophisticated kana to kanji converters (known collectively as input method editors, or IMEs, after the name of the Microsoft product), allow conversion of multiple kana words into kanji at once, freeing the user from having to do a conversion at each stage. The user can convert at any stage of input by pressing the space bar or henkan button, and the converter attempts to guess the correct division of words. Some IME programs display a brief definition of each word in order to help the user choose the correct kanji.
Sometimes the kana to kanji converter may guess the correct kanji for all the words, but if it does not, the cursor (arrow) keys may be used to move backwards and forwards between candidate words. If the selected word boundaries are incorrect, the word boundaries can be moved using the control key plus the arrow keys.
[edit] Learning systems
Modern systems learn the user's preferences for conversion and put the most recently selected candidates at the top of the conversion list, and also remember which words the user is likely to use when considering word boundaries.
[edit] Jump-ahead systems
The systems used on mobile phones go even further, and try to guess entire phrases or sentences. After a few kana have been entered, the phone automatically offers entire phrases or sentences as possible completion candidates, jumping beyond what has been input. This is usually based on words sent in previous messages.
