Someone asked me the other day about how laser printers work and it started me thinking about just how far we've come from the days of traditional printing and typography. It's interesting to think about how it all evolved and where the terminology came from and I took some time to write up a piece on the fundamental ideas (in a more article-type style then my usual posts).
Of Traditional Type, Typefaces, and Fonts
A piece of type is a rectangular block of metal with a raised character - a letter, numeral, or other symbol - in reverse on its upper end. The raised character constitutes the type piece's face, which when inked and pressed against a piece of paper or other material leaves an ink impression - a printed character. The printed characters produced from type are also called "type".
Most people would agree that a document is easiest to read when its characters all have the same style. That completely different characters - say, an "A" and an "o" - can in fact have the same style is a subtle point, similar to the notion that completely different pieces of furniture - say, a table and a chair - can have the same style. For printed characters to have the same style they must be produced from type whose faces all have the same style. Thus, such characters are said to have the same typeface. Typeface, then, is a property of a printed character.
In addition to the consistency of a document's style, most people would also agree that the style itself greatly helps determine the effectiveness of a document. Typeface design is thus an important art, and many thousands of typefaces exist. And just like furniture styles have names, like "Shaker" and "Country French", typefaces have names, too, like "Times Roman" and "Helvetica". Variations in a basic typeface lead to typeface families. For example, within the Univers typeface family are the typefaces Univers Italic, Univers Bold, etc. The characters in this piece all have the basic typeface Times New Roman.
A font is a complete assortment of type in a particular typeface and size. If a piece of type is viewed face-on, its size can be measured as the vertical distance from the top of its face to the bottom. This indicates that type size is a reference to height, not of the raised character itself, but of the rectangular spatial cell within which the character exists. Type size is defined this way so that characters which we perceive to be "the same size" (another subtle point) really are. Notice that type width varies with each character, and so would not serve as the basis of size in the same way as height. It should also be noted that a character's height and width must stay in constant proportion to one another to maintain the integrity of the character's typeface, which means that height alone is in fact sufficient to describe a character's size. The unit used to measure type size is the point (pt; approximately 1/72 of an inch). A font is referred to by its typeface and point size, such as "Times New Roman - 12 point". The characters of this piece are 12 points in size.
In traditional typography, a piece to be printed begins as a customer's hand-written or typewritten document. Fonts are chosen, and the typesetter either manually or mechanically sets the necessary type for printing. In the simplest type of printing, the type are then inked and pressed onto paper. In offset printing, the type are instead greased and pressed onto a roller, forming an image; the roller is then inked and washed, leaving an inked image behind (the ink remains dissolved in the grease), which is then rolled onto paper.
In digital typography, a piece to be printed begins as a text file on a storage device (either created by the typesetter from a customer's hand-written or typewritten document, or copied from a customer's storage device). The typesetter uses typesetting software to load the file into memory and perform the typesetting operations on the text. During typesetting, each character is held in memory as a numeric code, and formed on a display as a pattern of tiny dots. The display forms a character's dot pattern from a bit pattern, or bit map, of the character sent to the display by the typesetting software.
Once a piece is typeset on the display, it can be saved as a file containing both the text and the embedded typesetting operations. This allows the piece to be typeset over many sessions. Ultimately, of course, the piece is printed using some form of electronic printing, the dominant form of which is laser printing.
Laser printing is an electronic form of offset printing, in that a laser printer prints by pressing an inked image, rather than inked type, against paper. Each character in the image is formed by a laser beam on a photoconductive drum as a pattern of tiny electrically charged dots to which ink electrostatically adheres. At sufficient dot density (measured in dots per inch, or dpi), print produced in this manner is identical to print produced with type (laser printers used for professional typesetting print at 1200 dpi or better, compared to the 300-600 dpi produced by typical office laser printers). Type size in the digital realm, by the way, is often measured in terms of dots on the display, or pixels (px), instead of points. The standard display dot density is 96 dpi. thus 12 pt equates to 16 px (12 points / 72 points/inch x 96 pixels/inch).
Like a display, a laser printer creates a character's dot pattern from a bit map of the character sent to the printer by the typesetting software. However, a character's display bit map will typically differ from its printer bit map, due to differences in the dot density capabilities of the display and printer.
Of Electronic Type, Typefaces, and Fonts
Where does typesetting software get a character's bit map? In the simplest case, electronic renditions of type are stored in a file directly in bit-mapped (or raster) format, and the typesetting software simply retrieves a character's bit map from the file. Bit-mapped type in a particular typeface and size form a bit-mapped font.
In the more complex but more flexible case, type are stored in a file in outline (or vector) format, and the typesetting software generates (or renders, or rasterizes) the character's bit map. Outline type in a particular typeface can be scaled to any point size dynamically and constitute a scalable typeface.
Scalable typeface technology requires less disk space and maintenance than bit-mapped font technology, because, thanks to scalability, it requires only one file per typeface, and uses the same file for both display and printer. In contrast, bit-mapped font files contain "hard-coded" renditions of characters in a specific typeface and size, for a specific device. Hence, a file per typeface/size/device combination is required, which can quickly lead to disk space and maintenance problems.
In all of this, software running on the typesetting computer is responsible for producing bit maps for the display and printer - i.e. the fonts and typefaces are "host-based". Host-based typeface technology works with any dot-addressable display or printer, which is it's principal advantage.
Another approach is to use "device-based" fonts and typefaces. In this approach, the device - not the computer - is responsible for producing bit maps. While not used with displays, this approach is common with printers. In fact, laser printers typically have a number of bit-mapped fonts and scalable typefaces stored in ROM, and allow a user to download additional ones (called "soft" fonts or typefaces) into the printer's RAM.
In the case of device-based printer fonts and typefaces, the printer itself - not the typesetting software - does the work of producing character bit maps. Here, the typesetting software sends characters to the printer in their original form: as numeric codes rather than bit maps. Desired fonts or typefaces are indicated by sending control statements to the printer along with the characters to be printed. The printer may either retrieve a character's bit map from a bit-mapped font, or the printer's raster image processor (RIP) may render it from a scalable typeface. In either case, the bit map is then sent to the printer's image-forming laser for printing.
The principle advantage to using device-based printer fonts and typefaces is efficiency - since the computer does not have to produce bit maps, it's CPU is available again to the user more quickly. Furthermore, with scalable typefaces, a printer's special-purpose RIP may render faster than the computer's general-purpose CPU.
Host-based and device-based printer fonts and typefaces may be used together. In those cases where the printer is not equipped with the desired font or typeface but the typesetting software is, the typesetting software generates the character bit maps as before.
Scalable Typeface Technologies
These days, of course, anyone equipped with a graphical word processing program and laser/inkjet printer can do their own typesetting (as they type!) and high-quality printing. In today's software and printers, scalable typeface technology - due to its flexibility - has largely supplanted bit‑mapped font technology. A number of competing technologies exist.
The first scalable typeface technology available for personal computers was Adobe Systems' PostScript technology, adopted by Apple in 1984 for use with the Macintosh.
PostScript is actually more than just a scalable typeface technology. While the scalable typeface specification known as the "Type 1" specification is at the heart of the technology, PostScript also consists of Adobe's PostScript page description language specification and an interpreter that processes PostScript language statements and renders Type 1 typefaces.
Originally, PostScript was available only as a bundled, printer-based technology (Apple LaserWriters, for example, had the PostScript interpreter and a number of Type 1 typefaces stored in ROM). Furthermore, the Type 1 specification was secret, which meant that only Adobe could create PostScript-compatible typefaces.
However, Adobe published the Type 1 specification in 1990, allowing other type foundries to create PostScript-compatible typefaces. Originally these typefaces were used in Windows by installing the Windows version of Adobe Type Manager (ATM) .
Apple's TrueType scalable typeface technology first appeared in 1991 as part of the Macintosh's System 7 operating system. Microsoft licensed the technology for use in Windows starting with version 3.1. Originally TrueType in Windows was completely host-based, but printers quickly appeared that featureed built-in TrueType typefaces.
The Adobe and Microsoft OpenType scalable typeface technology uses Type 1 and TrueType outlines.Share on Twitter Share on Facebook