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Preparing Digital Files for Screen Printing

(October 2002) posted on Wed Oct 09, 2002

Learn how to make other types of artwork fit the screen-printing mold.

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By Mark A. Coudray

Screen printing's ability to produce high-quality graphics is also influenced by a long list of variables faced by no other printing process, such as mesh selection, screen tension, squeegee parameters, and a wide range of ink chemistries and characteristics. As a result, the graphic elements within a screen-printed design often require heavier trapping than images prepared for lithography or flexography.


If these corrections aren't made by the customer before you receive the file, it will be up to your own artists and prepress technicians to make the image ready for screen printing. Of course, it also will be up to your staff to determine the actual trapping parameters required based on the type of work you print and the capabilities of your shop. <P><B>Incorrect resolution</B>


The resolution issues with screen-printed graphics start as resolution issues with our digital artwork. As noted already, when outside designers create digital graphics for our customers, these files are produced for a variety of uses, but rarely for screen printing. And one of the biggest issues we face is that the graphic files are generally not created with the final size of the screen-printed image in mind.


For example, image files prepared for brochures do not work well when enlarged to produce bus graphics or other large-format displays. This is especially true when the graphic is a bitmap (e.g., TIFF, JPEG, EPS, or similar file format) designed for process-color reproduction. A bitmap may have been scanned at an appropriate resolution to support brochure-size reproduction, but as the size of the graphic increases, the resolution of the bitmap decreases.


To illustrate this concept, imagine a digital image created for use in a brochure. Say this image measures 4 x 6 in. and has a resolution of 300 dpi. Conventional wisdom holds that the resolution of a digital image needs to be roughly double the value of the line count you wish to print. So at its original size, this image could easily be reproduced as a 150-line halftone--an ideal line count for offset printing on a brochure.



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