 The magazine of the Melbourne PC User Group Desktop Publishing Introduced Ash Nallawalla ash@melbpc.org.au |
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Desktop Publishing (DTP) is a term coined by Jonathan Seybold, editor-in-chief of The Seybold Report on Publishing Systems, president of Seybold Seminars, sponsor of The Desktop Publishing Conference. (This term is also attributed to Paul Brainerd of Aldus Corporation.) DTP has no precise definition, and is comparable to the way Word Processing has no precise definition either. This allowed distributors and retailers in the early days to pass off almost anything as DTP. The 'Desktop' part of the term DTP merely refers to the fact that the machines used for DTP can be placed on top of an office desk. In this regard DTP hardware is distinguished from printing machinery.
Word Processing
Whereas word processing (WP) is almost exclusively confined to text, DTP involves the manipulation of text and graphics on screen. This distinction will blur over the next few years. A typical DTP setup includes a computer, text and graphics scanner, laser printer (or photo typesetter), and page composition software. Although most modern WP programs can talk to laser printers in order to produce typeset-like output, this is not DTP per se. The WP program may right-justify a page on the screen, and that is exactly the layout the laser printer will produce. This is fine for normal mono-spaced dot matrix or daisy wheel printers, where each letter occupies exactly the same space as another. A laser printer usually has available a proportional typeface such as the `Roman' fonts used on this page, where narrow letters such as '1' or 'i' take up less space than wider letters such as 'M' or 'W'. When a laser printer is used with a WP program, two things may happen - either the right margin will be preserved at the expense of big gaps between words or characters, or the right justification will be lost but with the characters correctly inter-spaced. The first likelihood is more common, but is a visual disaster. The very latest word processors now handle proportional fonts correctly.
Page Composition
A page composition (i.e. DTP) program takes text prepared by a WP program or that has been acquired by other means e.g. over the telephone via modem, or through a text scanner. It also takes graphic images drawn by drawing programs or scanned by a graphics scanner. The DTP program when handling text, for instance, can be told what typeface to use and what point size it will be. Taking this into account, it 'measures' each letter and keeps a running total against the pre-defined width of the page, allowing some spaces between letters and words. At a certain point along the text it will decide what is the last word to be placed on a given line, and will adjust the inter-character and inter-word spaces to give a clean appearance. Some better DTP programs will even hyphenate a word so as to reduce the white space on a line. The DTP program will even adjust the spacing between successive lines if you desire, and this is handy for squeezing in an extra line which may otherwise have spilled over to the next page. This is why a typeset page contains many more (almost three times) words than a word processed page. A DTP program should provide a WYSIWYG (What you see is what you get) image of the printed page on the screen in several 'zoom' sizes, up to 16 pages at a time! Naturally, the text is unreadable when viewing 16 pages, but it allows you to look at the document for aesthetics, particularly when viewing only two opposite pages.
DTP Programs
There are many so-called DTP programs that will handle text just like a printer's typesetting machine does, but fail in the graphics department. Some can accept only 'business graphics' i.e. pie charts, bar graphs and the like, but not drawings or scanned photographs. Some have all the above features, but do not have software support by way of other useful programs. For instance, the Apple Macintosh computer used to be the clear leader when teamed with the PageMaker DTP program. Today the Mac has other good programs available for it and the IBM is catching up. There is also a functionally-identical PageMaker version (and at least two other comparable DTP programs) for the IBM-PC, but the IBM user of the program is at a slight disadvantage. Reason: there are hundreds of ancillary graphics programs available for the Macintosh, such as borders, canned images, etc but there are not many for the IBM. The reason has been that the Macintosh has been until now a 'closed architecture' machine, where many custom-made chips have been made for Apple, which forces programmers and software programmers to conform 100% with the design. The customised chips used in the Mac also force all programs to use its input/output features in a certain way. This makes it very easy for a Mac user to learn a new program, as the same type of menu is used to achieve similar functions. The IBM-PC on the other hand has an 'open architecture', using off-the-shelf chips (except for a couple).
This helped make it the leading business PC, but also created a vast 'clone'
market for Taiwan and Japan. These clones were initially illegal, as they had to copy some IBM chips, but
eventually they were able to create a legal, near-copy that placed the BASIC language on a floppy disk
instead of a chip and a functionally identical Basic Input-Output System (BIOS) on a chip. Today, a clone
will run all major programs written for the IBM-PC - the software companies see to that. On the hardware
side, the IBM owner has a tremendous choice over what optional circuit boards he/she wants inside the
machine. Some software authors try to speed up their programs by making them 'talk' directly to the relevant
circuits, and not through the longer, conventional routes recommended by IBM. This is the type of situation
where hardware incompatibilities arise. These are determined by the choice of printer, VDU etc, but this fact
has made it difficult for the manufacturer of graphics hardware to produce a device that will sell in
quantity. Drawing programs from two suppliers will have different (and usually incompatible) graphics storage
formats, and this makes it difficult for someone else to produce a suite of fonts, borders etc to work with
every known graphics program. This is not the case with Macintosh software, which is written to meet the
machine's strict parameters.
Page Description Languages
A good DTP program also supports a Page Description Language (PDL). A PDL obviates the need for a laser
printer or photo-typesetter to store the details of every font (each size of a given typeface is a new font).
Each typeface is defined once mathematically, so that a larger or smaller point size is achieved merely by a
scaling formula. The leading PDL is PostScript by Adobe Inc, with Xerox's InterPress a distant second. IBM
Corporation has adopted PostScript as its PDL standard. Hewlett Packard was going to support one called DDL,
but at present its laser printers require their fonts to be loaded via a cartridge or disk. They now endorse
a PostScript add-in board for the PC. A PDL not only supports text but also drawings. An `object oriented'
drawing is also a mathematical description, as opposed to a bit map of little dots line by line. This allows
the PDL to store drawings and scanned images economically, and create special effects such as 'shadows' of
text, grid patterns, frames and hatching. PostScript is very slow when it is printing graphics, but it is
nevertheless the most popular.
Reprinted from the September 1988 issue of PC Update, the
magazine of Melbourne PC User Group, Australia
