Broadly, there are three categories of problem that occur when files are imaged:
If your files chew up excessive amounts of time during imagesetting, you will pay in cash, lost time or lost quality. Overtime charges or late film deliveries are obvious hazards, but reduced quality can be harder to spot. Film may change size during marathon sessions. A minor change may subtly shift color, while major changes may noticeably affect register.A graphic or font is missing, so there is a hole where a picture should be or the type has reflowed.
The file takes an excessive time to process.
The file produces fatal error messages or causes the RIP to crash.
On the other hand, if your files run smoothly, you can expect to be treated as a valued customer. Find out from your service bureau which functions cause problems with their equipment. Whenever aesthetically possible, you can then substitute simpler design elements for machine-intensive techniques.
Alternatives to complex techniques
Few of the techniques listed in this topic are outright show-stoppers by themselves. Combined with other complex techniques in a big file, they may slow imaging to a crawl. Therefore, artists and designers should think twice before using them. It's not possible to give absolute guidance about what combinations are lethal, because RIPs and imagesetters are always improving. On the other hand, artists and designers are always dreaming up new ways to complexify a file. Good preflight technicians develop a sixth sense of what will fly and what will die.
For example, the "Pattern" or "Tile" commands can save you work in making a repeating pattern of PostScript graphics, but it does make the RIP work hard. If your outline is complex, or the rest of the page is complex, it's better to take a few minutes to copy and paste your outline instead of patterning or tiling. These few additional minutes may save you a long delay at the output stage.
Alternatively, picture rotation must be done in the creator app, not the page design program. Page design applications rotate only the preview image; rotation of the high-resolution image is left to the RIP. A new location must be calculated for each pixel in the image, a task which is slow at best and which may defeat a RIP.
Processing time grows with the amount of information that the imagesetter must process and the complexity of the operations that have to be performed. There are legitimate reasons for size and complexity. However, a number of common practices cause unnecessary problems.
Missing elements
Missing elements are largely a matter of file housekeeping. The major page design applications now include or offer additions and extensions that help ensure that all images and fonts are present when the file is sent. Note that graphics may be collected automatically, but fonts are not.
As a final check, you should print separations on your laser printer. These are also an invaluable reference for the service bureau.
Excessive complexity
Illustration and page design programs can easily create files that are impossibly time-consuming or simply impossible to run through an imagesetter. The difference between overly long processing times and RIP crashes is often merely the degree of complexity that has been built into the file.
Generally, complexity in vector illustration files grows with the number of control points. By reducing control points, you reduce the file complexity and potential imagesetting problems.
Imaging problems in halftones are usually traced to a combination of size with the demand for a processor-intensive change, such as picture rotation or extreme scaling.
Nesting is a major source of problems in page files. The page will only output correctly when links are set up correctly. Simplicity helps. When files are deeply nested, as when an EPS graphic with a separate font is nested inside another EPS halftone inside a page file, the possibilities for trouble are excellent. Such a combination offers a multitude of complex links plus the host of unnecessary information contained in the structure of each EPS file.
Your own laser printer is a good guide to a file's complexity. If a page takes an unusual length of time to emerge from a 300 dpi laser printer, it may crash a high-resolution imagesetter. In addition, neither film nor the imagesetter are perfectly stable during an overnight marathon, even in a controlled atmosphere. During an overly long session, the film dimensions can change sufficiently to affect register and create ugly moirČ.
About ColorExpert
ColorExpert 1.1 is a comprehensive guide to digital color. We also publish ColorCourse/Photography, ColorCourse/Illustration and ColorCourse/Imagesetting.
The ColorCourses are co-published by Peachpit Press of Berkeley, CA (800/283-9444 or 510/548-4393,
ColorExpert products are endorsed by the International Prepress Association and the Association for Graphic Arts Training. If you belong to IPA, call Member Services to order.
Save only visible images
To render the lower drawing, the imagesetter must process all the shapes beyond the first row of columns. Yet they are invisible in the finished image. By deleting these unseen layers, you can save much imaging time.
Comments or suggestion to WebMaster david@TreeO.com (David E. Le Vine) © copyright 1995-96 TreeO Enterprises Inc. All rights reserved.
This excerpt from ColorExpert 1.1 ©Copyright 1996 ColorExpert Inc. All rights reserved.
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