Category: Techwriter
Most of today's applications and plenty of freeware for Windows can work very well with PDF. Even Microsoft caved in and now supports exporting to PDF from their Office products. Linux applications, from browsers to utilities, has long had the ability to export to PDF without any further plugins or external PDF engines. Not surprisingly, however, most publishers still adhere to the use of Adobe's publishing family of products simply because of its native support for PDF.
InDesign, like most Adobe products, has a few preset PDF settings configured for print and web. However, users shouldn't limit themselves to these presets and should freely modify or create their own. If the output PDF is intended for digital distribution but the images (high-resolution or otherwise) don't look right when compressed to PDF, then all it takes is a quick tweak of the downsampling settings.
Example 1: PDF Smallest File settings
This InDesign PDF consists of a photograph of an optical cable, an EPS image of an optical cable, and a screen capture of Windows 7's hardware settings.
At 100% Zoom, the vector EPS image looks perfect and so does the screenshot, which was taken using Lightscreen. The JPEG optical cable placed on the InDesign, however, appears pixelated. This document would be fine for the web but would fair poorly when printed commercially.
Example 2: Smallest file size settings with Downsampling switched off
1. To switch off downsampling, click Compression on the Export to PDF settings.
2. Under the Color images section, select Do Not Downsample (Bicubic downsampling is the default setting).
3. The resulting image of the JPEG optical cable in the PDF is somewhat smoother than the result seen from the PDF preset with downsampling.
Although the example above didn't produce a huge difference in terms of the JPEG quality, the results are more obvious with images that already has a resolution meant for the web (96 or 72 dpi). Switching off color image downsampling tells InDesign not to compress the color JPEG, GIF, TIFF, or PNG any further. Surprisingly, the use of low-resolution screenshots in InDesign documents happens pretty often for technical writers. Switching off downsampling won't solve a poorly selected image, but can at least help remove compression artifacts.
Users can experiment with changing the downsampling settings by switching JPEG to ZIP or JPEG 2000, or using subsamping/average downsampling to find the best image results. The Image quality setting doesn't have an immediate effect on the PDF image though it does greatly affect file size. Example 1 above was a paltry 93 KB while example 2 was a "huge" 931 KB. Thankfully, with broadband speeds and hardware reaching unprecedented speeds, somewhat larger PDFs are more acceptable today. Even tablets such as the Kindle Fire and Barnes N'Noble Nook, which aren't as powerful as the iPad and Asus Transformers Prime, can easily handle large PDFs.
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