Offset Printing (The Prepress)

Printing is still a very important industry, even though electronic media has taken some of it’s role in spreading knowledge through Internet and e-documents in today modern world. Printing items such as books, brochures, fliers, calendars and much more, however are still needed in their old fashion way.When we talk about off-set printing most people will think that it only involves the process of transferring images from printing plates to paper (press) using the printing machine, however, the actual printing processes that we have to consider start from receiving manuscript or draft making until the final finish products. It can be divided into three parts, that are, prepress, press and post press. In this article as an introduction, I will try to elaborate the first part of the printing processes.

The Prepress

Prepress processes include the work of draft layout, typesetting, graphic designing, proofreading, copy editing, page assembly, color separating, film producing and plate making. In modern printing technology this process is also known as Desktop Publishing (DTP). Typesetter or graphic designers who are responsible in carrying out this job usually have good skills, knowledge and talent in manipulating some of the commercial graphic or image editing software for instance Illustrator, Photoshop and InDesign (of the Adobe Creative Suite), Adobe Pagemaker, QuarkXPress, CorelDraw, Microsoft Publisher or the free open source software such as Inkscape, (with capabilities similar to Illustrator, Freehand and CorelDraw) and Scribus, program that brings professional page layout to Linux/Unix, MacOS X, and Windows desktops with a combination of press-ready output and new approaches to page layout and also supports professional publishing features, such as CMYK color, separations, ICC color management and versatile PDF creation.

Nowadays, the images created in the Desktop Publishing (DTP) application can be output directly to printing plates and are called Computer To Plate (CTP) output - such as Suprasetter thermal CTP system from Heidelberg, Elantrix H CTP system from Agfa etc. Whereas in older technology, images are firstly produced to films - Computer To Film (CTF) using the imagesetter, and then it will be contacted and exposed to plates in an exposing machine. The resolution on a typical image setter is 1270 or 2540 dpi with a maximum dpi of 4000.

In a single color printing items such as a text book content, only one plate will be produced using one of the above plate making process, where as in full color items such as colorful brochures, color images will be separated into 4 colors that are Cyan, Magenta, Yellow and Black and abbreviated as CMYK to produce 4 printing plates. Even in some printing items, additional plates (for spot colors – such as gold, silver or customized colors) are needed.

Plate making processes have a very important role in determining the quality of the item to be produced. The machine has to be professionally calibrated, because a slightest different in images screen or density of one of the plates, may result in bad printing outputs.

The good produced plates will be used in the second part of the printing processes, that is the Press.