Of all the technologies we use every day, there are probably few we take for granted as much as digital typography. It's just letters and numbers and punctuation, after all. How hard can it be?
It's usual to think of text and graphics as separate things when using a computer, but to a computer the screen or printer page is nothing more than an enormous grid of tiny pixels. When it comes down to it, displaying text on a modern computer is just a specialised kind of computer graphics - making it far from a trivial task.
The obvious approach is to store the visual representation of each character of a font as a little pixel image, and when that character has to be displayed simply copy the pixels to the screen at the desired location. Fonts like this are called bitmapped fonts because the pixels are represented directly by binary bits in the font.
Bitmapped fonts have severe limitations. First, to allow the font to be used at different sizes, you have to create and store separate images for each character at each size, covering as wide a range of sizes as is practical. Even worse, different screens and printers have different resolutions, meaning that they pack a different number of pixels into the same area. If you take a bitmapped font intended for display on a low-resolution device like a monitor and use it on a high-resolution device like a laser printer then the characters will come out microscopic in the paper version because the pixels that make them up are much smaller on the printer than on the screen. Some devices don't even have square pixels, which will distort the characters if not accounted for.
The solution to both of these problems is to use outline fonts rather than bitmapped ones. Outline fonts don't store pixel images of their characters. Instead they store abstract mathematical descriptions of the outlines of the characters, without referring to any particular size or output device. When a font is needed for a particular device at a particular size the outlines are scaled by the computer to match those specifications and then converted on the fly into pixel images that can be displayed.
Outline fonts have their own difficulties, mind you. At very small sizes, where the strokes that make up a character are around a pixel wide, the conversion to a pixel image may produce ugly results: some strokes are drawn using two pixels and others disappear completely. To counteract this outline fonts usually contain hints or even small programs for adjusting the outlines at small sizes to make sure the outcome is pleasing to the eye. The text on a computer screen may seem like the boring bit, but it's really one of the more sophisticated parts of modern computing. Good typography doesn't just look good, it helps the reader out. Bad typography will ruin the finest content, so the very fact modern computers quietly get on with the job of displaying text without calling attention to themselves is proof all that complexity behind the scenes is worthwhile.
- The Press