Halfwidth and fullwidth forms: Difference between revisions

Revision as of 07:20, 21 May 2012

Latest revision as of 03:28, 12 June 2025

(159 intermediate revisions by 87 users not shown)

Line 1:

{{Short description|Alternative width characters in East Asian typography}}

{{Unreferenced section|date=March 2007}}

{{For|the Unicode chart block|Halfwidth and Fullwidth Forms (Unicode block)}}

[[File:KoreanDOSPrompt.png|thumb|349px|A Korean command prompt (cmd.exe) showing halfwidth and fullwidth characters.]]

[[File:Command Prompt on Windows XP (Korean).png|thumb|349px|A command prompt ([[cmd.exe]]) with Korean localisation, showing halfwidth and fullwidth characters]]
In [[CJK characters|CJK]] (Chinese, Japanese, and Korean) computing, [[graphic character]]s are traditionally classed into '''fullwidth''' (in{{efn|In [[Taiwan]] and [[Hong Kong]]: [[wikt:全形|全形]]; in CJK: [[wikt:全角|全角]]).}} and '''halfwidth''' (in{{efn|In [[Taiwan]] and [[Hong Kong]]: [[wikt:半形|半形]]; in CJK: [[wikt:半角|半角]]).}} characters. WithUnlike fixed-width[[monospaced fontsfont]]s, a halfwidth character occupies half the width of a fullwidth character, hence the name.

''[[Halfwidth and Fullwidth Forms (Unicode block)|Halfwidth and Fullwidth Forms]]'' is also the name of a [[Unicode block]] U+FF00–FFEF, provided so that older encodings containing both halfwidth and fullwidth characters can have lossless translation to and from Unicode.

In the days of [[computer terminal]]s and [[text mode]] computing, characters were normally laid out in a grid, often 80 columns by 24 or 25 lines. Each character was displayed as a small [[dot matrix]], often about 8 [[pixel]]s wide, and an [[SBCS]] (single byte character set) was generally used to encode characters of western languages.

==Rationale==

For a number of practical and aesthetic reasons, [[Han character]]s would need to be twice as wide as these fixed-width SBCS characters. These "fullwidth characters" were typically encoded in a [[DBCS]] (double byte character set), although less common systems used other variable-width character sets that used more bytes per character.

{{More citations needed section|date=April 2021}}

[[File:Alternative names of JIS X 0213.svg|thumb|Characters which appear in both [[JIS X 0201]] (single byte) and [[JIS X 0208]] / [[JIS X 0213]] (double byte) have both a halfwidth and a fullwidth form in [[Shift JIS]].|class=skin-invert]]

In the days of [[computer terminal]]s and [[text mode]] computing, Western characters were normally laid out in a grid on the screen, often 80 columns by 24 or 25 lines. Each character was displayed as a small [[dot matrix]], often about 8 [[pixel]]s wide, and an [[SBCS]] (single -byte character set) was generally used to encode characters of westernWestern languages.

For aesthetic reasons and readability, it is preferable for [[Chinese characters]] to be approximately square-shaped, therefore twice as wide as these fixed-width SBCS characters. As these were typically encoded in a [[double-byte character set|DBCS]] (double-byte character set), this also meant that their width on screen in a [[duospaced font]] was proportional to their byte length. Some terminals and editing programs could not deal with double-byte characters starting at odd columns, only even ones (some could not even put double-byte and single-byte characters in the same line). So the DBCS sets generally included Roman characters and digits also, for use alongside the CJK characters in the same line.

''Halfwidth and Fullwidth Forms'' is also the name of a '''[[Unicode block]]''' U+FF00–FFEF.

On the other hand, early Japanese computing used a single-byte code page called [[JIS X 0201]] for [[katakana]]. These would be rendered at the same width as the other single-byte characters, making them [[half-width kana]] characters rather than normally proportioned kana. Although the JIS X 0201 standard itself did not specify half-width display for katakana, this became the visually distinguishing feature in [[Shift JIS]] between the single-byte JIS X 0201 and double-byte [[JIS X 0208]] katakana. Some IBM code pages used a similar treatment for [[Hangul#Letters|Korean jamo]],<ref name="ibm933">{{cite web |url=http://demo.icu-project.org/icu-bin/convexp?conv=ibm-933 |title=ICU Demonstration - Converter Explorer |website=demo.icu-project.org |access-date=7 May 2018}}</ref> based on the [[KS C 5601#1974|N-byte Hangul code]] and its [[EBCDIC]] translation.

==In Unicode==

''{{see also|Halfwidth and Fullwidth Forms'' is also the name of a '''[[(Unicode block]]''' U+FF00&ndash;FFEF.)}}

In [[Unicode]], if a certain [[grapheme]] can be represented as either a fullwidth character or a halfwidth character, it is said to have both a ''fullwidth form'' and a ''halfwidth form''.

For compatibility with existing character sets that contained both half- and fullwidth versions of the same character, [[Unicode]] allocated a single block at U+FF00&ndash;FFEF containing the necessary "alternative width" characters. This includes a fullwidth version of all the [[ASCII]] characters and some non-ASCII punctuation such as the Yen sign, halfwidth versions of katakana and [[hangul]], and halfwidth versions of some other symbols such as circles. Only characters needed for lossless round trip to existing character sets were allocated, rather than (for instance) making a fullwidth version of every Latin accented character.

Unicode assigns ''every'' code point an "East Asian width" [[Unicode character property|property]]. This may be:<ref name="uax11">{{cite web |url=https://unicode.org/reports/tr11/ |title=Unicode® Standard Annex #11: East Asian Width |last1=Lunde |first1=Ken |author-link=Ken Lunde |publisher=[[Unicode Consortium]] |date=2019-01-25}}</ref>

''Halfwidth and Fullwidth Forms'' is the name of [[Unicode block]] U+FF00&ndash;FFEF, the last of the [[Basic Multilingual Plane]] excepting the short [[Unicode Specials|Specials]] block at U+FFF0&ndash;FFFF.

{|class=wikitable

Range U+FF01&ndash;FF5E reproduces the characters of [[ASCII]] 21 to 7E as fullwidth forms, that is, a fixed width form used in [[CJK]] computing. This is useful for typesetting Latin characters in a [[CJK]] environment. U+FF00 does not correspond to a fullwidth ASCII 20 (space character), since that role is already fulfilled by U+3000 "[[ideographic space]]."

|+Unicode character properties based on width

|-

!scope="col"|Abbreviation

!scope="col"|Name

!scope="col"|Description

|-

!scope="row"|W

|Wide||Naturally wide character, e.g. [[Hiragana]].

|-

!scope="row"|Na

|Narrow||Naturally narrow character, e.g. [[ISO Basic Latin alphabet]].

|-

!scope="row"|F

|Fullwidth||Wide variant with [[NFKC|compatibility normalisation]] to naturally narrow character, e.g. fullwidth Latin script.

|-

!scope="row"|H

|Halfwidth||Narrow variant with [[NFKC|compatibility normalisation]] to naturally wide character, e.g. [[half-width kana]]. Includes U+20A9 ([[won sign|₩]]) as an exception.

|-

!scope="row"|A

|Ambiguous||Characters included in East Asian DBCS codes but also in European SBCS codes, e.g. [[Greek alphabet]]. Duospaced behaviour can consequently vary.

|-

!scope="row"|N

|Neutral||Characters which do not appear in East Asian DBCS codes, e.g. [[Devanagari]].

|}

[[Terminal emulator]]s can use this property to decide whether a character should consume one or two "columns" when figuring out tabs and cursor position.

Range U+FF65&ndash;FFDC encodes halfwidth forms of [[Katakana]] and [[Hangul]] characters – see [[half-width kana]]. Range U+FFE0&ndash;FFEE includes fullwidth and halfwidth symbols.

==ChartIn OpenType==

[[OpenType]] has the <code>fwid</code>, <code>halt</code>, <code>hwid</code>, and <code>vhal</code> feature tags to be used to reproduce fullwidth or halfwidth form of a character. [[CSS]] provides control over these features using <code>font-variant-east-asian</code> and <code>font-feature-settings</code> properties.<ref>{{cite web |url=https://helpx.adobe.com/fonts/using/open-type-syntax.html |title=Syntax for OpenType features in CSS |publisher=[[Adobe Inc.|Adobe]] |access-date=2023-09-20}}</ref>

{{Unicode chart Halfwidth and Fullwidth Forms}}

==See also==

* [[CJK Symbols and Punctuation (Unicode block)|East Asian punctuation]]

*[[CJK]]

* [[Em size]] – full width forms

*[[Han unification]]

* [[Enclosed Alphanumerics]] – bullet point sequences; some appear as fullwidth (e.g. ⒈, ⓵, ⑴, ⒜, ⓐ)

*[[Half-width kana]]

* [[Han unification]]

*[[Monospace (disambiguation)]]

* [[Hangul Jamo (Unicode block)]]

*[[East Asian punctuation (disambiguation)]]

* [[Katakana (Unicode block)]]

* [[Latin script in Unicode]]

==Notes==

{{Notelist}}

==References==

{{Reflist}}

==External links==

* [https://www.unicode.org/reports/tr11/tr11-31.html East Asian Width] Unicode Standard Annex #11

*http://www.alanwood.net/unicode/halfwidth_and_fullwidth_forms.html

*http://everything2.com/index.pl?node=Halfwidth%20and%20Fullwidth%20Forms

*Fullwidth character converter [http://www.businessinfo.co.uk/labs/hackvertor/hackvertor.php?input=PEB1bmlfaHdmd19jaGFycz4iPjxzY3JpcHQ%2BYWxlcnQoMSk8L3NjcmlwdD48QC91bmlfaHdmd19jaGFycz4%3D]

{{Unicode navigation}}

[[Category:UnicodeEast blocksAsian typography]]

[[Category:Kana]]

[[Category:Hangul jamo|*Halfwidth]]

[[de:Unicodeblock Halbbreite und vollbreite Formen]]

[[ko:전각 문자와 반각 문자]]

[[ja:全角と半角]]

[[zh:全形和半形]]