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APS » Journals » Frequently Asked Questions About PostScript

Frequently Asked Questions About PostScript

Table of Contents

Introduction

INTRODUCTION

The purpose of this FAQ is to describe some basics of the PostScript file format, specific properties of the APS PostScript files, and how to use the APS PostScript files.

 This FAQ makes several assumptions about the user and the type of system that's being used:

  1. You have a connection to the Internet, either by dialup or through a direct connection. If you are dialing in, you want a modem that will support speeds of at least 14,400 bits/sec or faster. Slower modems can be used but a pot of coffee will be required while waiting for documents to download.
  2. You have a web browser and are familiar with downloading and installing files on your system.
  3. You are working with a graphics capable system.
  4. If you're using a Unix System that is not directly supported by Ghostscript, you should have someone available who can help you compile and install the Ghostscript source.

What is PostScript?

PostScript is a programming language that describes the appearance of text, graphics, and images. It may be used for on-screen display or for printing hardcopy. A PostScript file is a high-level, device-independent way of representing page images.

What options are used in APS PostScript files?

Level 1 vs. Level 2

This refers to the level of implementation of the PostScript language. Level 2 is more recent than Level 1, and is more complex with greater capabilities. The decision to offer Level 2 was based on requests from subscribers to offer smaller Postscript files; Level 2 files are significantly smaller than Level 1 files.

In order to make the upgrade as seamless as possible, while Level 2 files will be the default throughout, the Level 1 Postscript files will still be available for those who may have trouble printing Level 2 files. To access the Level 1 files, you will have to edit the URL directly by changing ps to ps1. If you're using Netscape Navigator 3.0 or later, all you do is right click on the Postscript file you wish to download which will bring up a small menu. Select the item, ``Copy Link Location''. Now go to the address box at the top of the browser and highlight the text. Then open the edit menu at the top and select paste. Now go back to the address box and change ps to ps1 and then hit enter. You will now be downloading the Level 1 Postscript file.

Beginning with the current issue (May 1), going forward, all the file sizes listed will reflect the Level 2 Postscript file sizes. All Volumes will serve Level 2 Postscript by default. File sizes on prior issues will be corrected as time permits since they all represent Level 1 Postscript file sizes.

Fonts

A font is a set of characters in a certain style, such as Times Roman, Helvetica Bold, or Roma Italic, which usually includes the alphabet, numbers, and some special symbols. When a word processor or other typesetting software creates a document, certain font information is used to create the images for the characters that are called for in that document. A PostScript file may contain full font information, subsetted font information, or no font information. Full fonts means that even if only one character in a font is used, the entire set of characters is put into the PostScript file. Subsetted fonts means that only the characters needed are embedded in the PostScript file.

 After extensive research, the APS has determined that it is not legal for us to embed the full font information in our PostScript files because we use proprietary fonts and the vendors must protect against piracy. Therefore, we only embed the minimal font subsets necessary to produce an image of our printed pages. An advantage of this is that the resulting PostScript file is smaller.

Graphics

The original graphics in our PostScript files (produced at 600 dots per inch, or 1200 dots per inch) have been downsampled to 300 dots per inch. This also results in a smaller PostScript file. 

How do I view PostScript files?

Ghostscript

Aladdin Enterprises distributes a program called Ghostscript, which was created to print PostScript documents to non-PostScript printers. (The current version of Ghostscript, 5.50, will now allow you to view and print PDF files too.) You can obtain Ghostscript here. Once you have entered the site, just select the appropriate version for your system.

When you download Ghostscript, please be sure you download all the needed files, especially the fonts, even if you have an existing copy of Ghostscript. Failure to do this will result in less than optimal performance. The Ghostscript package is not very simple to install, but once it is installed and configured, you should have no problem viewing PostScript files. Important Ghostscript documentation is contained in the "use.txt" and the "make.txt" (if you're compiling your own version) files. Please read all the "*.txt" files prior to using Ghostscript.

Currently, Ghostscript (version 5.50) prints both Level 2 and Level 1 PostScript. If you are using Ghostscript version 3.53, and require Level 1 PostScript, you will have to upgrade to Ghostscript 5.50.

Ghostview

Ghostscript comes with limited viewer capabilities. If you don't mind stepping through a document one page at a time, you can use Ghostscript. If you'd like something that will allow you to navigate more efficiently, you can download Ghostview. Ghostview, a viewer that adds extra control to the Ghostscript engine, requires that you have Ghostscript installed on your system. To make Ghostscript as easy to use as possible, we recommend you install Ghostview.

If you use the modified version of Ghostview to view your PostScript files, you'll have to configure your browser to spawn Ghostview when you encounter a PostScript file. The command for Mosaic and Netscape would look something like this:
application/postscript; ghostview %s

 In the case of Netscape and Windows Mosaic, you can make these changes interactively using the options/preferences menu. In version 2.6 of XMosaic, you'll have to add the line
application/postscript; ghostview %s
to your .mailcap file which should be in your home directory. The Mosaic online manual has help on this subject.

How do I print PostScript files?

The Level 2 PostScript we offer should be able to print on any printer that supports Level 2 PostScript. Level 2 printers should also be able to print Level 1 files since they are meant to be backward-compatible, but if your printer does not support Level 2 Postscript, you'll have to download the Level 1 Postscript versions of the files. For help downloading the Level 1 files, see the instructions above. Keep in mind that if you do download the Level 1 files, they could be more than 10 times larger than the Level 2 files so transmission times may be high.

Last modified: Fri Nov 20 12:10 EST 1998