Taking Advantage of PostScript

323 Pages·2001·1.99 MB·English

Taking Advantage of PostScript
John F. Sherman

Taking Advantage of PostScript
John F. Sherman
University of Notre Dame
Art, Art History & Design
University of Notre Dame
Notre Dame, IN 46556 5639
[email protected]

Chapter 1
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intro
Designers face a new requirement: to acquire and master a digital craft. The
traditional crafts of color theory, design, typography and drawing have always
been required for the designer. All of these are important and I do not advocate
their dismissal. But the need for a digital craft is becoming more apparent as the
innovations of technology arrive faster and faster.
Designers, however, cannot focus on simply being well-trained users of expensive
pieces of hardware and software. By mastering the technology, they can reach a
point where innovative new solutions to visual communication problems can be
discovered.
The process by which an image can be made has changed dramatically. An image
can be constructed by a combination of hand drawings, video capture, and
computer programming. The finished image provides a solution by means of
faster investigation, greater choices, and new creative possibilities.
Digital craft entails learning a new language — a visual language. The greater the
depth of understanding and experience in a language, the greater the vision of
what can exist in the mind of the creator. Different languages allow different
realities to exist. Many of the images created for this book are visual ideas that have
been made into images by writing them down. They can only be achieved by an
intimate knowledge of the PostScript language. I find it exciting that there are
images that can only be created by writing a PostScript program. Understanding
PostScript is one major avenue to mastering the technology of producing graphics.
1.1 why learn PostScript ?
Why learn PostScript when there are so many good graphics programs available
that are much easier to use than programming? There are two answers.
First, knowing the PostScript Page Description Language (PDL) gives the designer
an insight into graphics software based on the PostScript image mode. The
PostScript PDL has strengths and weaknesses. Having this knowledge base builds
confidence because it permits you to work with the strengths of software and not
with false expectations. When something does not work as expected, you may be
able to devise a way to work around or attack the problem from another direction.
Second, the PostScript language is a richer graphics language than what is made
available by menu selections and dialog boxes in all the graphics software
packages available. There are visual opportunities available to you that are only
available by programming. A design you write in PostScript might supplement a
packaged technique in a software program or be written totally in PostScript code.
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Taking Advantage of PostScript
Either way, you are in control of the design process.
1.2 PostScript’s background
PostScript is a page description language developed by Adobe Systems
Incorporated. PostScript resides within a printer and acts as an interpreter for the
data sent to it by either a software program or an original program written by a
programmer. A page description language is the means through which a printer
prepares a page containing text, line art, and digitized images. The page is
constructed pixel by pixel (dot by dot). The size of dot will depend on the printer,
and ranges from 300 to 2540 dots per inch (dpi). A 300 dpi printer will draw a 1
inch square 300 dots to a side, while a 2540 dpi printer will draw the square 2540
dots per side. Figures 1–1 and 1–2 are the same shape; they have the same
description. The dotted line is the true shape. What will be different is the quality
of its presentation through either printing or a monitor’s display. The greater the
resolution provided, the closer to the true description the shape will appear.
figure 1–1
Figure 1–2 is the same shape with double the resolution.
figure 1–2
The most widely known example of a 300 dpi printer is the Apple LaserWriter. The
Linotron L100 has a maximum resolution of 1270 dpi and can be set to print at 600
and 300 dpi. The Linotron L300 is also available with a maximum printing
resolution of 2540 dpi. The advantage of using the increased resolutions of these
printers is that a greater number of visually distinct grays can be produced. The
Linotron L100 can produce about one hundred visually separate gray levels
because of its fine dot pattern.
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Chapter 1
The PostScript language is printer independent, enabling you to alternate from one
brand of printer to another without making any changes to the original document.
All the major original equipment manufacturers of high resolution printers have
licensed PostScript for their printers making it the de facto industry standard. The
designer can use a low cost laser printer for sketching and then later use the more
costly high resolution imagesetters when the design is completed. The difference
in the resolution changes the rendering quality and the number of distinct grays
that can be depicted.
Until recently, a laser printer equipped with a PostScript interpreter was the only
means to see the designs created by writing PostScript programs. Display
PostScript is an adaptation of the PostScript PDL from Adobe Systems Inc. for use
on computer monitors, and the NeXT computer is the only computer that uses it.
Display PostScript is to the graphic display of computer monitors as the PostScript
PDL is to different laser printers. It provides a common imaging model for the
graphic display (screen description language) and the laser printer. The Macintosh
uses the QuickDraw language for its screen display and a file’s data is converted
from QuickDraw to PostScript for printing. Because of this, the full richness of the
PostScript language cannot be used and then viewed on the Macintosh screen.
Display PostScript is monitor independent and automatically takes advantage of
the full capabilities (gray levels or color) of the computer’s monitor without having
to rewrite the part of the software responsible for the graphic display. Display
PostScript has several advantages. Most importantly, what is seen on the screen
very closely matches what is printed. The only difference is the resolution of the
image on the monitor compared to the resolution of the image ultimately printed
on the laser printer. For example, in drawing a 1 inch square, the square would be
drawn with ninety-two pixels per side (resolution of the NeXT monitor) and the
same information would be used again and sent to the laser printer to create the
square at 300 dpi or more.
1.3 organization of this book
Taking Advantage of PostScript is divided into four major parts.
Chapters 2–7 of this book will introduce some basic PostScript concepts and
drawing techniques. Chapter 4 will show how these simple programs can be saved
as EPS files to be used within other programs. Most of the simple beginning
programs are more easily drawn in a variety of graphics software programs, but
they are the building blocks to the more complicated programming techniques that
come in later chapters.
Chapters 8–17 will cover advanced PostScript techniques that unleash the power
of the PostScript Page Description Language. Much of what is covered here cannot
be accomplished in available graphics software. Chapter 17 covers some advanced
programming techniques and takes several designs step by step and explains how
and why they were written as they are. Chapter 18 will touch on some of the new
features of PostScript Level 2.
Chapters 19 and 20 of this book are libraries of numerous examples of PostScript
programs that can be the starting point for new designs. They generally
concentrate on one visual idea or programming technique. Chapter 21 is a gallery
of images.
The final section of the book contains several reference appendixes.
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Taking Advantage of PostScript
1.4 formats used in this book
The main narrative of this book is in the font you are now reading.
All PostScript program listings or the mention of a PostScript operator will be set
in Courier Bold and look like this:
PostScript code % comment
Notes or comments (explained in more detail in section 2.5) will be set in regular
Courier to help set them off from the program. At times, when more lengthy
annotation is required, I’ll bracket the explanation like this for better legibility and
to save space:
% --------------------------------------------------------
Extended comments; not part of the program.
% --------------------------------------------------------
learPnS When you see this symbol in the margin, it means that the PostScript program is
available on disk for experimentation within the companion LearnPS tutorial.
There will be a version for both Macintosh and NeXT computers. The LearnPS
1–1
animation symbol may also indicate that the PostScript program for an illustration is
available or that an animation demonstrating a particular point is available. Use
the number or title below the symbol to help you locate the file in LearnPS. Most of
the PostScript examples in this book are written to appear on a grid representing
the bottom left corner of a page.
A PostScript program will be listed below the graphic it produces. In this way, it
will serve as a title for the graphic. Otherwise, a graphic title will be found in the
left margin.
Each chapter is divided into sections. We are now in section 1.4, meaning chapter
1 section 4. Often in this book I’ll refer to other sections using this system.
1.5 getting started
Writing a simple original PostScript program is a fairly easy task to accomplish.
You most likely already have the tools needed if you have a Macintosh computer
and PostScript equipped printer. The program file can be written with any word
processing program that can save standard ASCII text files. An ASCII text file is a
standard form of saving text that all computers understand. It cannot, however,
contain specialized formatting that most applications provide, such as variable
point sizes, font styles, or graphics.
On the Macintosh you will need:
Software to write the program. Microsoft Word, MacWrite, WriteNow and
others will work fine. You may find it convenient to use a text editor designed
for working only with text files.
A utility to send the file to the PostScript printer. The most common is SendPS
from Adobe.
A PostScript equipped printer, to interpret your files.
On the NeXT:
The NeXT computer comes with all the software you’ll need to send the file to
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Chapter 1
the printer or monitor.
Chapter 2 covers getting started in more detail.
1.6 options for downloading files
There are quite a few utilities to send or download a PostScript file to a printer. On
the Macintosh I have used these, but there are many others:
LaserStatus DA from CE Software
SendPS from Adobe Systems
Downloader from Adobe Systems
I have two favorite ways of working on the Macintosh. One option is to write the
file using QUED (QUality EDitor) from Paracomp. QUED is a text editor; it only
opens and saves files as text. I then send the PostScript file to the printer with
LaserStatus. Since LaserStatus is a Desk Accessory, I can easily switch back and forth
between editor and downloader while developing a design. It looks like this
below:
The second method is again to use QUED to write the program, but send the file to
the printer using either Adobe’s SendPS or Downloader. The primary difference
between the two utilities is where the standard output file is directed. This file may
be an error message or feedback from the printer. With SendPS, the error messages
and feedback are sent to a file on your computer’s disk. This is handy since at times
the message can flash by quickly or you may need the information that is sent back.
The advantage of Downloader is that those messages are sent to a window on the
Macintosh screen. The standard output file will come up a number times later in
section 16.1 and the utilities appendix.
You will be able to send PostScript files to your printer from within LearnPS.
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intro
Taking Advantage of PostScript
6 overview of the basics