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Taking Advantage of Postscript 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 cchapterha1pter 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. intro 1 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. 2 intro 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. intro 3 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. % -------------------------------------------------------- When you see this symbol in the margin, it means that the PostScript program is learnPS available on disk for experimentation within the companion LearnPS tutorial. 1–1 There will be a version for both Macintosh and NeXT computers. The LearnPS 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.
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