Font hinting (also known as instructing) is the use of mathematical instructions to adjust the display of an
outline font
A computer font is implemented as a digital data file containing a set of graphically related glyphs. A computer font is designed and created using a font editor. A computer font specifically designed for the computer screen, and not for print ...
so that it lines up with a
rasterized
In computer graphics, rasterisation (British English) or rasterization (American English) is the task of taking an image described in a vector graphics format (shapes) and converting it into a raster image (a series of pixels, dots or lines, whic ...
grid. At low
screen resolution
The display resolution or display modes of a digital television, computer monitor or display device is the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resolution i ...
s, hinting is critical for producing clear, legible text. It can be accompanied by
antialiasing Anti-aliasing may refer to any of a number of techniques to combat the problems of aliasing in a sampled signal such as a digital image or digital audio recording.
Specific topics in anti-aliasing include:
* Anti-aliasing filter, a filter used be ...
and (on
liquid crystal displays)
subpixel rendering
Subpixel rendering is a way to increase the apparent resolution of a computer's liquid crystal display (LCD) or organic light-emitting diode (OLED) display by rendering pixels to take into account the screen type's physical properties. It takes ...
for further clarity.
Overview
For the purpose of on-screen text display, font hinting designates which primary pixels are
interpolated
In the mathematical field of numerical analysis, interpolation is a type of estimation, a method of constructing (finding) new data points based on the range of a discrete set of known data points.
In engineering and science, one often has a n ...
to more clearly render a font. Hints are usually created in a
font editor during the typeface design process and embedded in the font. A font can be hinted either automatically (through processed algorithms based on the character outlines) or set manually. Most font editors are able to do automatic hinting, and this approach is suitable for many fonts. However, high-quality commercial fonts are often manually hinted to provide the sharpest appearance on computer displays.
Verdana
Verdana is a humanist sans-serif typeface designed by Matthew Carter for Microsoft Corporation, with hand-hinting done by Thomas Rickner, then at Monotype. Demand for such a typeface was recognized by Virginia Howlett of Microsoft's typograph ...
is one example of a font that contains a large amount of hinting data, much of which was accomplished manually by type engineer
Tom Rickner.
Implementations
In the
TrueType
TrueType is an outline font standard developed by Apple in the late 1980s as a competitor to Adobe's Type 1 fonts used in PostScript. It has become the most common format for fonts on the classic Mac OS, macOS, and Microsoft Windows operating ...
font format, released in 1991 by
Apple Inc
Apple Inc. is an American multinational technology company headquartered in Cupertino, California, United States. Apple is the largest technology company by revenue (totaling in 2021) and, as of June 2022, is the world's biggest company ...
, hinting invokes tables of font data used to render fonts properly on screen. One aspect of TrueType hinting is ''
grid-fitting'', which modifies the height and width of font characters to line up to the set pixel grid of screen display. The open-source
FreeType 2 font rendering engine uses an auto-hinter when such hinting data are not present or their use is restricted by a
software patent
A software patent is a patent on a piece of software, such as a computer program, libraries, user interface, or algorithm.
Background
A patent is a set of exclusionary rights granted by a state to a patent holder for a limited period of time, u ...
.
As of 2011, the FreeType Web site states that the relevant font hinting patents have now all expired, and hinting is now enabled in FreeType by default.
[
]
Guidelines
According to the TrueType Reference Manual,[https://developer.apple.com/fonts/TTRefMan/RM03/Chap3.html#features TrueType Reference Manual] font instructors (those performing font hinting) must balance the following two constraints when hinting a font:
* At small sizes, chance effects should not be allowed to magnify small differences in the original outline design of a glyph.
* At large sizes, the subtlety of the original design should emerge.x-height
upright 2.0, alt=A diagram showing the line terms used in typography
In typography, the x-height, or corpus size, is the distance between the baseline and the mean line of lowercase letters in a typeface. Typically, this is the height of the le ...
, and baseline, so that the font retains its normal character while not producing exaggerated effects at small sizes.
See also
* Kell factor
The Kell factor, named after RCA engineer Raymond D. Kell, is a parameter used to limit the bandwidth of a sampled image signal to avoid the appearance of beat frequency patterns when displaying the image in a discrete display device, usually ...
References
External links
*
An online font hinting tool
*
The Raster Tragedy at Low-Resolution Revisited: Opportunities and Challenges beyond "Delta-Hinting"
'. Beat Stamm. March 2011. A revised and extended version of th
original 1998 article
covering anti-aliasing including sub-pixel rendering, opportunities made possible by anti-aliasing, challenges in the rasterizer and elsewhere, and a discussion of font hinting in the context of these opportunities and challenges.
Tutorial on the DejaVu font wiki
Article from the Anti-Grain Geometry Project.
Hinting
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