LaTeX and fonts

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http://mintaka.sdsu.edu/GF/bibliog/latex/fonts.html

TeX (or LaTeX) knows only the metrics of a font. The layout engine simply arranges the glyphs' bounding boxes in rows (lines of type).

But the post-processors that prepare the formatted page image for display on a terminal or printing on paper must be able to fill in the glyphs. Ultimately, that's done by breaking each glyph into arrays of little dots (like drops of ink from an injet printer): a bitmap.

However, to get the best result, the fonts should not be reduced to bitmaps until the final stages of display. For example, a computer terminal can display shades of gray, and so partly makes up for its poor resolution by shading the pixels that lie on the edge of a glyph — a process called anti-aliasing.

Resolution

A typical computer screen has about 100 dots per inch (dpi) these days. When text or graphics are displayed on the screen, that's the pixel density that is used to represent the glyphs you see.

On the other hand, printers typically have resolutions from 300 to 1200 dpi (or even more for commercial image-setters). The glyphs that represent the font characters have to be "rasterized" at the resolution of the printer.

This difference in resolution means that the actual representation of a font glyph in terms of dots is different on different output devices. But, to be portable, a formatted document must not depend on the resolution of the final output device; and TeX has no way to know the resolution of the device on which the document will be printed or displayed.

Hence, the output from the TeX compiler is a device-independent (DVI) file. It tells where each glyph goes, but says nothing about the representation of the glyph's shape as a two-dimensional array of dots — i.e., a bitmap.

So the glyphs that compose the text aren't present in the *.dvi file that LaTeX produces. It merely reserves space for them. But they must be present when the file is printed or displayed. The information about glyph shapes comes from font files.

documented on: 2008-06-21