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Generally, a font in the computing world refers to a set of glyphs (a single character, e.g. "A", or a symbol such as a dingbat) available in different sizes and faces. There are generally three kinds of fonts: bitmap, outline and stroke.

  • A bitmap font consists of a series of dots or pixels representing the image of each glyph in each face and size.
  • An outline font uses drawing instructions or mathematical formulas to describe each glyph.
  • Stroke fonts use a series of specified lines and additional information to define the profile, or size and shape of the line in a specific face and size, which together describe the appearance of the glyph.
Bitmap fonts are faster and easier to use in computer code, but are inflexible for resizing or changing font faces as they require a separate font for each size and each face. Outline and stroke fonts can be resized or refaced using a single font and substituting different measurements for components of each glyph (e.g. the letter "A" has three components, the two lines on the outside and the bar between the two outside lines, and may have more depending on whether the outside lines have serifs, the additional base lines at the bottom and/or top), but are somewhat more complicated to use than bitmap fonts as they require additional computer code to render them.

A comparison to the format of image files on computer may be appropriate here. Image file formats such as Windows Bitmap (.BMP), Portable Network Graphics (.PNG), Joint Photographic Experts Group (.JPG or .JPEG) and Tagged Image Format (.TIF or .TIFF), among others, are bitmap image formats, and store the entire image as a series of dots, one at a time, in some cases with compression. Image files using the Windows Metafile format (.WMF) and Scalable Vector Graphics format (.SVG) are types of outline or stroke image formats, and store descriptions of how to draw the image rather than storing the image itself. A bitmap image is usually difficult to display in a different size without some distortion (but can be displayed quickly); an outline or stroke format can be very easily resized (but takes more time to render as it must be drawn from scratch each time it is displayed).

Font types and formats

Bitmap fonts

Bitmap fonts are simply collections of raster images of glyphs. For each variant of the font, there is a complete set of glyph images, with each set containing an image for each character. For example, if a font has 3 sizes, and any combination of bold and italic, then there must be 12 complete sets of images.

Some systems using bitmap fonts can create some font variants algorithmically. For example, the original Apple Macintosh computer could produce bold by widening vertical strokes and oblique by shearing the image. Scaling the images is also possible; algorithms for this can vary in quality from blocky (nearest neighbor resampling) to high quality (Scale2x and hq3x).

Bitmap fonts are not widespread anymore, because other font encoding methods are superior in visual quality and flexibility. In some situations, however, they are still useful. Bitmap fonts are used in the Linux console, the Windows recovery console, and embedded systems.

Outline fonts

Type 1 and Type 3 Fonts
Type 1 and Type 3 fonts were developed by Adobe for professional digital typesetting. Using PostScript, the glyphs are described with Bezier curves, and thus one set of glyphs can be resized through simple mathematical transformations. In practice, however, very large or very small versions of a font need extra hints to look good. Type 1 fonts used Adobe's proprietary hinting system, which was very expensive. Type 3 fonts were the same as the Type 1 without the hints, and thus looked good only at normal sizes.

TrueType Font
TrueType is a font system originally developed by Apple Computer. It was intended to replace Type 1 fonts, which many felt were too expensive. Like Type 1 fonts, Bezier curves are used to describe the glyphs. It is currently very popular and implementations exist for all major operating systems.

Stroke-based font

A glyph's outline is defined by the vertices of individual strokes and stroke's profile. Its advantage over outline fonts include reducing number of vertices needed to define a glyph, allowing same vertices to be used to generate a different font that have different weight, glyph width, or serifs using different stroke rules, and the associated size savings. For font developer, editing a glyph by stroke is easier and less prone to error than editing outlines. Stroke-based system also allows rescaling glyphs without altering stroke thickness of the base glyphs. It is heavily marketed for East Asian markets for use on embedded devices, but the technology is not limited to ideograms.

Commercial developers included Agfa Monotype (iType), Type Solutions, Inc. (owned by Bitstream Inc.) (Font Fusion (FFS), btX2), Fontworks (Gaiji Master), which have independently developed stroke-based font types and font engines.

Although Monotype and Bitstream have claimed tremendous space saving using stroke-based font on East Asian character sets, most of the saving comes from building composite glyphs, which is part of TrueType specification.

METAFONT
METAFONT uses a different sort of glyph description. Like TrueType, it is a mathematical font description system, but describes glyphs through the strokes of a circular pen. This means that glyphs produced with METAFONT generally do not have sharp points, as the pen tip is of finite size.

Editors

See also

External links

Digital typography

 

This article is licensed under the GNU Free Documentation License. It uses material from the "Computer font".

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