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PDF: The Cure for Dawdling Digital Files

(December 1999) posted on Tue Dec 14, 1999

Learn the basics of creating PDF files.

click an image below to view slideshow

By Mark A. Coudray

LZW This format is based on the Lempel-Ziv-Welch (LZW) data-compression algorithm, licensed from Unisys. It is lossless and works best when there are large areas of flat color. It is ideal for images created with vector-based drawing programs. It is not designed for use with continuous-tone images and can actually increase file size if applied to them.


ZIP Another lossless compression method, ZIP works in much the same way as the LZW method, but it can result in file sizes up to 20% smaller than comparable LZW files. It also does not work well on continuous-tone images.


Run Length Encoding This method is used for compressing monotone information. The most common example is compression of black-and-white text. Run length encoding is lossless and can result in very small file sizes.


Acrobat allows us to select compression information for each of the three types of PostScript images--color bitmap, grayscale bitmap, or monochrome bitmap. We can select downsampling resolution levels, as well as the specific compression formats for either automatic or manual compression. Be aware that different image types may require different compression levels to minimize file size. <B>Figure 1</B> shows typical settings for a PDF graphic file that will be used for screen printing


PDF tools

To create PDF files, we need the Adobe Acrobat 3.0 Suite of products, which includes PDF Writer, Distiller, Exchange, and Reader. The products are available from most computer software dealers.


Acrobat PDF Writer Acrobat provides two methods of making PDF files. The first utilizes the Acrobat PDF Writer, which can generate a PDF file from images created on just about any desktop illustration program. PDF Writer is not intended for high-resolution prepress work, but rather for publishing documents in PDF format for easy transport over the Internet, intranet, LAN, or between different platforms. It provides an excellent format for sending spreadsheets, word processing documents with simple graphics, and simple color proofs, especially if they are designed for viewing on a computer screen.


To use PDF Writer, we simply choose it as the printer when we're ready to output the graphic from our design application<B> (Figure 2)</B>. The graphic will be converted into a file with a .pdf extension. It then can be viewed and printed from any computer using Acrobat Reader.



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