Prepress is the term used in the printing and publishng industries for the processes and procedures that occur between the procurement of a written manuscript and original artwork, and the manufacture of a printing plate, image carrier, or (traditionally) forme, ready for mounting on a printing press.Prepress
The printing process has three stages—prepress, press, and binding or postpress. In small print shops, job printers are usually responsible for all three stages. They check proofs for errors and print clarity and correct mistakes, print the job, and attach each copy pages together. In most printing firms, however, each of the stages is the responsibility of a specialized group of workers. Prepress technicians and workers are responsible for the first stage, preparing the material for printing presses. They perform a variety of tasks involved with transforming text and pictures into finished pages and making printing plates of the pages.

How Prepress works
Prepress comments describe the placement and size of scanned images, as well as cropping information and any adjustments to the size, brightness, or contrast. for example, when you lay out a publication in InDesign, you use the standard tools to place, re-size, and crop scanned images (usually, TIFF files that are lower resolution versions of a high resolution scan). When the layout is complete and you are ready to print separations, you print a composite PostScript file to disk using either the InDesign "Prepress File" or "EPS" export options or by printing PostScript to a file. InDesign embeds the Prepress comments (the name and position of each scanned image, cropping information, and any adjustments to the size, brightness, or contrast) in the PostScript file. This file is comparatively small since it does not normally include any scanned image data.

You can then send the PostScript file to a prepress system or layout information is extracted and used to find a high resolution image and insert the image data into the PostScript print stream to the imagesetter.

How to works Platemakers
Platemakers for a long time used a photographic process to make printing plates. The flat, a layout sheet onto which a negative has been attached, was placed on top of a thin metal plate coated with a light-sensitive resin. Exposure to ultraviolet light activated the chemical in parts of the plate not protected by the film dark areas. The plate was then developed in a solution that removes the unexposed nonimage area, exposing bare metal. The chemical on areas of the plate exposed to the light hardened and became water repellent. The hardened parts of the plate form the text and images to be printed. Now, the printing industry has largely moved to technology known as direct-to-plate by which the prepress technicians send the data directly to a plating system, by-passing the need for stripping film onto a flat.

Color Separations
Prepress does not require that the image be preseparated. If the Prepress server is able to perform RGB to CYMK conversions, then those conversions can take place on-the-fly during the final printing process. This approach has two advantages: it requires much less disk space, since a high-resolution CMYK version of the image is never stored on disk; and it gives greater separation flexibility, since it allows the image to be stored in the more device-independent RGB form during the entire prepress cycle.

In most modern publishing environments, the tasks related to content generation and refinement are carried out separately from other prepress tasks, and are commonly characterized as part of graphic design. Some companies combine the roles of graphic design and prepress production into desktop publishing.

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