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Offset Book Printing
Offset (also known as photo-offset) is the most common process for printing books, and will be for the foreseeable future. Whereas digital printing entails a fixed cost per unit, offset printing provides for economies of scale: the more units printed in one run, the lower the unit cost (to a point). Presently offset is generally cheaper than digital printing for runs of over 1,000.
Types of Offset Presses
There are three main types of press:
- Sheetfeed press. Because it prints one sheet at a time, this is the slowest process, and also the most expensive. On the other hand, it yields the highest quality. Best for small print runs (2,000-3,000), two or more colors, or illustration work.
- Web press. In this process, paper issues continuously from a large roll, feeds through at high speeds, and is chopped and folded as it emerges into 32-page sections, or "signatures." Web press printing is relatively inexpensive, used mostly for one color jobs (black ink), and best for runs above 5,000.
- Belt press. Used for trade books and magazines, this is a direct impression method that uses a web press, and combines printing and binding. Paperbacks emerge completely finished at the end and hardcovers need only jackets to complete them. However, you can print only one color, and elegant typeface and halftones do not print well.
Other Traditional Printing Methods
- Letter press. This is a traditional, rarely used method in which books are set in hot metal.
- Gravure. Gravure uses millions of tiny dots to form images. Also used by magazines and Sunday newspaper supplements, gravure is a preferred method for large-format books with high-quality photos or reproductions of artworks. It is economical for print-runs of 200,000 or more.
The Offset Process
- Offset printing begins with the publisher providing a typeset manuscript, complete with line art illustrations and halftones (if any) and cover art. Typesetting is frequently done in-house using software such as QuarkXpress or Pagemaker, or it may be outsourced to a prepress firm.
- If the manuscript is provided to the printer as hard copy ("camera-ready copy"), it is then pasted onto "boards" and photographed. At this point the printer may be asked to reduce and insert original art (photos) as half-tones. The image then is burned through the negatives onto a thin printing plate using a bright light. It is generally preferred and increasingly common for publishers to provide digital files. These can be imaged directly onto printing plates using lasers, eliminating a step and thereby improving quality and reducing costs.
- Once negatives have been made, they are exposed to photosensitive paper to create "blue lines." These are carefully examined by the publisher for imperfections, stray marks, etc.
- Separately, but well before printing, a copy of the cover is generated and sent to the publisher for approval.
- The actual printing begins. Ink is applied to the plates, which are in turn applied to long sheets of paper, which are gathered and folded into 16- or 32-page "signatures." The assembled signatures are then gathered and bound in one of the ways described in Book Binding.
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