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ETHIOPIAN SCIENCE & TECHNOLOGY

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Vol. 2, No. 4 ------------ < for cleo community> -------------- May 7, 1993


CONTENTS

What is PostScript? ....................................Section 1/6

How does PostScript work? ..............................Section 2/6

Designing Fonts ........................................Section 3/6

Doing Graphics .........................................Section 4/6

Application Software....................................Section 5/6

Your Assignment .......................................Section 6/6

Notes from the Editor

###Ethio Science & Technology### is a "weekly column" presented to the Cleo community. It covers various issues in the science; in particular, those of more related to Ethiopia.

Today's column is on PostScript, a language that is very popular around the world. PostScript may not be the bread and butter of hot technology for Ethiopia, but it's powerful and versatile nature is very tempting. We might as well face it and see where we can go with it.

This column, by no means can be taken as a sufficient materials to understand or for that matter to be well informed about PostScript. At most, it introduces what is out there!

Some important terms:-

dpi: dpi is an acronym for "Dot Per Inch." Among other factors a printer quality is measured by how much dpi it prints papers. If a printer is said that it can print 300dpi, that means it has a capability to put 300 dots with in 1 inch square.

Resolution: If a printer produces 1200dpi or above, it is said to be a high resolution printer. Resolution also apply to computers' screens. If your computer has an EGA adopter with 320 by 200 pixels, it is a low resolution screen. Mostly, today's monitors come with an adopter called Super VGA with a resolution of 1024 by 768 pixels.

Fonts: A sets of related characters including letters, numerals, and symbols that are designed and used for printing.

ASCII : American Standard Code for Information Interchange.

Section 1/5

What is PostScript?

Instead of giving a simple description of what PostScript is, I prefer to introduce it in terms of an example.

Let's say, you are a perfect artist who can write letters, draw graphics and images on pages-- page is being a printer or display monitor. Let's also assume that whenever you are describing letters, graphics, or images on pages, you have a strict and disciplined rules to communicate with your customers (users.) The customers or users are not allowed to communicate with you with out following the given rules. If they respect the rules, their request is fulfilled by you--whether drawing graphics or images. Remember also that you can rotate, scale, outline, and shadow letters. Your graphics drawing capability is so powerful, you are appreciated by many enthusiasts. Well, your are a PostScript!

A Postscript is a page description language. It is also device independent; in other words, a particular machine can adopt it as it is. Mostly, it comes with laser printers. If you compare the price of such printers with the one with out a PostScript, it is not hard to see the difference. If you don't have a PostScript printer, you are may be bound to see it's products somewhere in word processor, desktop publisher, spread sheet, and alike. That is you don't have the capability of full PostScript.

Section 2/5

How Does PostScript work?

PostScript is equipped with mathematical formulas to help draw omplex graphics. Simple statements such as the following tells PostScript to draw a line from point (0,0) to (200,200):

0 0 moveto

200 200 ruleto

stroke

showpage

PostScript is said to be an interpreter language, that is, unless you have a PostScript printer or compiler at your disposal, you just cannot write a program and generate a stand alone version of that program which you may take some places where there is no PostScript. Your instructions are interpreted and implemented immediately when you give them.

Most PostScript printers come with resident Postscript fonts. These fonts can be used either manually, or through application programs such as word processors. There are also loadable fonts which sometimes called soft fonts. One can load them to the printer and use them regularly. PostScript is good at scaling fonts to the desired points if the hardware permits. It doesn't maintain scaled fonts in its storage; instead, it keeps the minimum description (as mathematical formula) of that font. When asked to scale any font, it does so during the printing or displaying process-- consuming a minimum a storage space. Not only that, the quality (resolution) of the font is not reduced as a result of scaling.

More importantly, for gray scaling, similar to black and white photograph and newspapers, PostScript is a gun. If the hardware permits, one can produce from 0-255 variety with in a gray color.

(Section 3/5)

Designing Fonts

In PostScript, there are three forms of fonts--namely type-0, type-1, and type-3, and here I only cover two of them leaving the first one. Two of them are essential to us.

Type-1 fonts are more compact and constructed with strict procedures. Because of that to use these fonts, a full fledged PostScript is not required. That is way application programs are using them with non-PostScript printers or displaying devices.

Type-3 are user-defined fonts that require an interpreter. These fonts are clumsy and take more storage space. They can use any available drawing procedures.

If you would like to design your own fonts, you may pick one of these types that suits your purpose. The question is how one go about and design a font? Before trying to answer this question, let me give one advice. If you are really interested in designing a font, please expect to spend a considerable time on it and make sure that before you go to drawing board, you know what you want precisely. There are three approaches:

1. Using only a PostScript Printer: You can write a program or a description of your font with your favorite editor following PostScript rules. You don't see the result unless you send your program to the printer and view what it looks like. This is a crude and difficult way of producing font.

2. Using FontGrapher: This is an application program that enables you to design only Type-1 font with MS-Windows. It might cost about $270.00. You do your design work, while you view your work. You don't have to know PostScript language as much as you are required in approach (1).

3. Using GhostScript: Well, what is GhostScript? Are you familiar with GNU concept. If you are not, do not worry. I will have a column in the future.

GhostScript is a PostScript interpreter written by L. Peter Deutsch. You can preview your fonts with this system on your monitor if you have DOS, OS/2, or some other operating systems. Still, writing the program (description of a font) is your responsibility. You can enter your program in an interactive manner and view it right there.

What is wonderful about this system: it is distributed freely under the terms of the GNU Library General Public License. Note: if you would like to obtain this system, just do ftp at

prep.ai.mit.edu:/pub/gnu

If you don't have access to ftp, I can provide a copy for a volunteer who can then distribute it to all interested people (fair deal!)

----to be continued

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abassa@neosoft.com/
Abass Belay Alamnehe /
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