Halfwidth and fullwidth forms

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A command prompt (cmd.exe) with Korean Localisation showing halfwidth and fullwidth characters

In CJK (Chinese, Japanese and Korean) computing, graphic characters are traditionally classed into fullwidth (in Taiwan and Hong Kong: 全形; in CJK: 全角) and halfwidth (in Taiwan and Hong Kong: 半形; in CJK: 半角) characters. With fixed-width fonts, a halfwidth character occupies half the width of a fullwidth character, hence the name.

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/from Unicode.

Rationale[edit]

In the days of 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 pixels wide, and a SBCS (single byte character set) was generally used to encode characters of western languages.

For a number of practical and aesthetic reasons Han characters need to be square, approximately twice as wide as these fixed-width SBCS characters. As these were typically encoded in a DBCS (double byte character set) this also meant that their length 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.

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 Korean jamo, based on the N-byte Hangul code and its EBCDIC translation.

In Unicode[edit]

Halfwidth and Fullwidth Forms
RangeU+FF00..U+FFEF
(240 code points)
PlaneBMP
ScriptsHangul (52 char.)
Katakana (55 char.)
Latin (52 char.)
Common (66 char.)
Symbol setsVariant width characters
Assigned225 code points
Unused15 reserved code points
Unicode version history
1.0.0216 (+216)
1.0.1223 (+7)
3.2225 (+2)
Note: [1][2][3]

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.

Halfwidth and Fullwidth Forms is the name of Unicode block U+FF00–FFEF, the last of the Basic Multilingual Plane excepting the short Specials block at U+FFF0–FFFF.

Range U+FF01–FF5E reproduces the characters of ASCII 21 to 7E as fullwidth forms. U+FF00 does not correspond to a fullwidth ASCII 20 (space character), since that role is already fulfilled by U+3000 "ideographic space".

Range U+FF65–FF9F encodes halfwidth forms of katakana in a transposition of their JIS X 0201 layout – see half-width kana.

The range U+FFA0–FFDC encodes halfwidth forms of compatibility jamo characters for Hangul, in a transposition of their 1974 standard layout. It is used in the mapping of some IBM encodings for Korean.[4]

Range U+FFE0–FFEE includes fullwidth and halfwidth symbols.

Block[edit]

Halfwidth and Fullwidth Forms[1][2]
Official Unicode Consortium code chart (PDF)
  0 1 2 3 4 5 6 7 8 9 A B C D E F
U+FF0x
U+FF1x
U+FF2x
U+FF3x _
U+FF4x
U+FF5x
U+FF6x
U+FF7x ソ
U+FF8x
U+FF9x
U+FFAx  HW 
HF
U+FFBx
U+FFCx
U+FFDx
U+FFEx
Notes
1.^ As of Unicode version 12.0
2.^ Grey areas indicate non-assigned code points

The block has variation sequences defined for East Asian punctuation positional variants.[5][6] They use U+FE00 VARIATION SELECTOR-1 (VS01) and U+FE01 VARIATION SELECTOR-2 (VS02):

Variation sequences for punctuation alignment
U+ FF01 FF0C FF0E FF1A FF1B FF1F Description
base code point
base + VS01 !︀ ,︀ .︀ :︀ ;︀ ?︀ corner-justified form
base + VS02 !︁ ,︁ .︁ :︁ ;︁ ?︁ centered form

An additional variant is defined for a fullwidth zero with a short diagonal stroke: U+FF10 FULLWIDTH DIGIT ZERO, U+FE00 VS1 (0︀).[7][6]

History[edit]

The following Unicode-related documents record the purpose and process of defining specific characters in the Halfwidth and Fullwidth Forms block:

Version Final code points[a] Count L2 ID WG2 ID Document
1.0.0 U+FF01..FF5E, FF61..FFBE, FFC2..FFC7, FFCA..FFCF, FFD2..FFD7, FFDA..FFDC, FFE0..FFE6 216 (to be determined)
L2/15-268 Beeton, Barbara; Freytag, Asmus; Iancu, Laurențiu; Sargent, Murray (2015-10-30), Proposal to Represent the Slashed Zero Variant of Empty Set
L2/17-056 Lunde, Ken (2017-02-13), Proposal to add standardized variation sequences
L2/17-436 Lunde, Ken (2018-01-21), Proposal to add standardized variation sequences for fullwidth East Asian punctuation
L2/18-039 Anderson, Deborah; Whistler, Ken; Pournader, Roozbeh; Moore, Lisa; Liang, Hai; Cook, Richard (2018-01-19), "24. Fullwidth East Asian Punctuation", Recommendations to UTC #154 January 2018 on Script Proposals
1.0.1 U+FFE8..FFEE 7 (to be determined)
3.2 U+FF5F..FF60 2 L2/99-052 Freytag, Asmus (1999-02-05), The math pieces from the symbol font
L2/01-033 Karlsson, Kent; Freytag, Asmus (2001-01-16), Disunify braces/brackets for math, computing science, and Z notation from similar-looking CJK braces/brackets
L2/01-159 N2344 Ad-hoc report on Mathematical Symbols, 2001-04-03
L2/01-157 N2345R Karlsson, Kent (2001-04-04), Proposal to disunify certain fencing CJK punctuation marks from similar-looking Math fences
L2/01-168 Whistler, Ken (2001-04-10), Bracket Disunification & Normalization Hell
L2/01-223 Suignard, Michel (2001-05-23), Discussion of Issues Regarding Bracket Disunification
L2/01-317 Suignard, Michel (2001-08-14), Bracket Disunification & Normalization
L2/01-295R Moore, Lisa (2001-11-06), "Bracket Disunification and Normalization", Minutes from the UTC/L2 meeting #88
  1. ^ Proposed code points and characters names may differ from final code points and names

In OpenType[edit]

OpenType has the fwid, halt, hwid and vhal "feature tags" to be used for providing fullwidth or halfwidth form of a character.

See also[edit]

References[edit]

  1. ^ "Unicode 1.0.1 Addendum" (PDF). The Unicode Standard. 1992-11-03. Archived (PDF) from the original on 2016-07-02. Retrieved 2016-07-09.
  2. ^ "Unicode character database". The Unicode Standard. Archived from the original on 2016-07-10. Retrieved 2016-07-09.
  3. ^ "Enumerated Versions of The Unicode Standard". The Unicode Standard. Archived from the original on 2016-06-29. Retrieved 2016-07-09.
  4. ^ "ICU Demonstration - Converter Explorer". demo.icu-project.org. Retrieved 7 May 2018.
  5. ^ Lunde, Ken (2018-01-21). "L2/17-436: Proposal to add standardized variation sequences for fullwidth East Asian punctuation" (PDF).
  6. ^ a b "Unicode Character Database: Standardized Variation Sequences". The Unicode Consortium.
  7. ^ Beeton, Barbara; Freytag, Asmus; Iancu, Laurențiu; Sargent, Murray (2015-10-30). "L2/15-268: Proposal to Represent the Slashed Zero Variant of Empty Set" (PDF).

External links[edit]