A computer font is a file containing a description of a set of alphabetic, numeric, service and pseudographic characters used to display these characters (in particular text) by a program or operating system.
Concept of computer font
It should be distinguished:
- Font as a set of characters created by an artist;
- The font is like a computer file;
- Font as a set of metallic characters used in typographical printing.
A set of fonts that have a similar pattern but differ in style (regular, italic, bold, etc.) is called a typeface. For example, the fonts "Arial", "Arial Bold", "Arial Italic", and "Arial Italic Bold" make up one "Arial" typeface.
Font (from the English font) is a computer slang term that replaces the word "font". Often used more narrowly, meaning "font file". Sometimes it replaces the term "headset".
On computers, a font is a data block (or file) consisting of descriptions of individual characters in a set, used by a program (or part of the graphical shell of the operating system) when displaying text. For text modes, the font is stored directly in the video adapter (either in its permanent memory or in operational memory).
Types of computer fonts
By internal arrangement
Computer fonts are divided into two types according to the method of rendering: raster and vector.
- In raster fonts, each character is described as a set of dots (pixels) located at the nodes of the raster grid - that is, in fact, it is a regular bitmap. Bitmap fonts are not suitable for high-quality printing and are used primarily in text-based programs and in the console. They were widely used in the era of dot matrix printers and low resolution monitors.
- In vector (or outline) fonts, characters are curvilinear outlines described by mathematical formulas. Each sign is described using vectors that define the coordinates of reference points, which are connected by straight lines or curves and form the outline of the sign without reference to the absolute size or resolution. This description makes it easy to scale the image without losing quality, which is not possible with bitmap fonts. Vector fonts look the same on screen as they do on paper. There are several different vector font formats that differ in the way font information is stored and presented: PostScript Type1, TrueType, OpenType.
To output a vector font to raster devices (monitors and printers), it must be rasterized - converted into a set of dots. Adobe Type Manager (ATM) was designed to install and rasterize such fonts on Windows 9x/NT/2000 and Mac OS operating systems. In Windows NT 4.0, you can also use PostScript Type1 fonts without installing ATM, although they are automatically converted to TrueType format during installation, with all the ensuing consequences. Windows 2000 (and later) already has a built-in Type1 font rasterizer, and ATM is no longer required to install them.
By character width
According to the width of the characters, fonts are divided into monospaced and proportional.
- In a monospace font, all characters are the same width. In early computers, this made it possible to simplify the task of displaying text on the screen: each character was located within its familiarity, and the image of the character was drawn as a fixed-size drawing, so the width of the character was not required, and the procedure for setting the position of the character on the screen became extremely simple. Another advantage of monospace fonts is that the relative position of characters on the screen is unambiguous, regardless of the typeface, which is a prerequisite for preformatting printing. This allows you to display tables and pseudo-graphics using only font characters, as well as create ASCII art. However, monospaced fonts have certain disadvantages: first of all, a larger set width, uneven pattern, as well as difficulties in displaying "wide" letters, such as "Ш" or "W": at a small resolution, they can become completely unrecognizable. Fixed-space fonts are used primarily in terminal emulators, as well as in the interfaces of development environments. Also, a monospaced font is used to display code listings to emphasize their "computer" origin.
- In a proportional font, characters can have different widths. For example, the letter l will take up significantly less space than the letter W. This allows you to significantly reduce the average character size, while maintaining readability. Text typed in a proportional font looks neater and is better readable at large volumes. Proportional font is almost always used for printing and displaying texts.
Screen display
A feature of displaying texts on the screen is a significantly lower resolution than is achievable on paper even for not the most advanced technology. In this regard, vector fonts on the screen are reproduced with distortions. In order to avoid these distortions, various methods are used:
- Hints are a set of instructions that improve the shape of a character displayed on the screen.
- Monochromatic anti-aliasing - allows you to get rid of the "angularity" of the symbol by partially painting over pixels that are not completely covered by the lines of the symbol.
- Sub-pixel anti-aliasing is an extension of the anti-aliasing function based on the properties of LCD monitors: in them, each pixel is divided into three sub-pixels of different colors, each of which can be controlled separately, which allows to theoretically increase the horizontal resolution by 3 times. In practice, there are many limitations: in addition to the need to maintain color balance, a significant increase in resolution is hindered by the difference in the perception of different colors by the human eye: green seems brighter, while red is more saturated. Therefore, when changing the order of colors, various side effects will be observed: “smearing” lines, color fringing, etc. Despite this, fonts after applying subpixel anti-aliasing look much better on the LCD screen than with monochromatic anti-aliasing.
Some font formats may have special instructions to improve their display: for example, to match adjacent characters in a font, there may be several options for the style of the same character, as well as instructions for using one or another style.
Source: ru.wikipedia.org
