|
|
|
|
Bitmap vs. Outline : a short history of computer font.
Explaining the difference between Bitmap
and Outline fonts implies a little travel into time. At the very beginning
of Computers, and especialy on Macintosh, fonts were only Bitmaps. This means that they were
described for the screen (and eventually for the printer if you had one)
as an image, and to be more precise, an array of dots. A bit-map
is a rectangular grid in wich every square is black or white (on or off):
the bitmap file indicates precisely wich one. So in a bitmapped font,
characters are represented as a pattern of dot in a grid. The smaller
the dots the finest the drawing, and as printers are generally able to generate
at least 300 dots per inch (DPI), the dots are indistinguishables. Bitmapped
fonts were the legacy on Macintosh till around 1986, either for screen restitution
than for printing matters.
A first advantage of bitmapped font is that printing a font is only a question of sending the right bit
to the right place. They also makes it easy to fill or shade characters.
But they also have a real disavantage: as a bitmap represents a letter at a particular size, it
is not scalable. A 12 points "e" drawed on a 300 dpi grid
is not drawn as well as a 24 points one (there is less point to shape its
form). So you can't just enlarge a 12pt to draw a 24pt ; you must have the
two files to print them at a specific definition. This was, for example,
a real pain in the ass when precise typographic works were to be done.
That's the reason why, since the apparition of outline fonts, bitmapped
Fonts are now getting obsolete (see below). But this technology is still
used on Macintosh, and on most of computer OS : the screen font of a type 1 are bitmaps, and
the reason why you don't see the dots on your screen is that you are probably
using ATM (Adobe Type Manager), an init and control panel that improve the
scren restitution by calculating the missing screenfonts from the one avaliables.
AND HERE COOMES AGAIN THE MATHEMATICS...
The advent of outline
font technology was the very starting point of desktop publishing (or to
be more precise, its taking off).
Outline fonts are describing
characters mathematicaly, as a series of curves and lines.
So they are fully scalable and have unlimited resolution;
they can be printed at any size.
Different methods
are used to describe the outline; Type 1, 3 or type 5 fonts are using
Postscript. Because printer are still using little dots to print on
a sheet of paper, the printing process of Outline Fonts involves rasterization
: the characters are transformed into dots "on the fly" by a RIP
(Raster Image Processor), using the outline information.
This
process can either occurs in the computer or in the printer. For example,
Postscript printers includes a device that rasterize the Type 1 font, while
this process is done in the computer for Type 3 (using a "BuildChar"
routine included in the font).
Added to the outline file,
an outline fonts also features screen files, and hints. Screen
files are the informations normaly used for screen restitution. The hints
are indications on how to place the dots in order to obtain the best restitution
at a specific definition (i.e. for a specific numbers of dots in the grid).
The First outline technology was using Postscript and gave birth to the
type 1 fonts. This particular language is owned by Adobe system
inc. and describe a page using Bezier curves (a system invented by the
french mathematician Bézier). If you are using Adobe Illustrator,
you have a fair idea of how it works, since it was originally uniquely a
Postscript user-friendly programming software : each thing you are allowed
to do when building a graphic object corresponds to a Postscript function.
You can even read Postscript if you open an EPS (Encapsulated PostScript)
file generated by Illustrator with a text editor (simple text, word or any
other). It will consists in a text describing the graphism, featuring numbers
(coordinates of points and tangents), and words (functions successively
applied to build the graphism).
IS THERE LIFE AFTER POSTSCRIPT?
Adobe also proposed to use this technology for screen restitution, and the Display
Postscript system was adopted in 1988 by steve Jobbs's NeXT computer.
Some attemps of third-party Postscript fonts were done, like Type 3 fonts,
but did not questionned Adobe's supremacy.
The fact that the Postscript
language is owned by someone else, added to the high cost of licençing
it, probably explains why Apple did not adopted Display Postscript when
Adobe proposed it the first time. Apple even developped an alternative graphic
environnement named QuickDraw GX that gave birth to the True Types.
True Types (originaly named Royal fonts) were developped with Microsoft
in the early 1990s, in order to challenge the supremacy of Postscript fonts
and Postscript technology.
Today the True type rendering engine is included in both Mac and Windows OSs.
So the non-bitmap option seems to have win. But even if they don't need Bitmap Files, these
outline fonts often features some (explanations at the True Type section),
and so, bitmap Fonts are not, in a sense, really obsolete.
The latest developement
in font technology, the Open Fonts, are a superset
of Type 1 fonts and True types, and so are an outline format
Finally, since the joint-venture
of NeXT and Apple in 1998, there's no news about the adoption of Display Postscript on Macintosh
(one of the futuristic features of Steve Jobs' NeXT OS was the inclusion of Postscript Technology
in the System). MacOS X with its dFont format doesn't seem to have gone further in that direction...
So Bitmaps are doomed at short or middle range terms, but still alive!
|
|
|
|
|
|
|
|
|
