PDF compression tools

Introduction

You'd be forgiven for thinking that the lack of a Mac OS X-native version of Adobe Distiller is a serious drawback for PDF creation. Not true. By using PDF as a standard within OS X, and supporting it through the Quartz rendering system and the continued development of Jaguar, Apple has made it possible for almost any application to create a PDF easily. Some applications, such as Adobe InDesign, offer an export option with control over all the usual parameters including image compression, font embedding and subsetting, and colour space. Others make use of the Save as PDF option in Mac OS X's print dialog. Either way, creating a PDF has never been easier. So why do we need tools to enhance, repurpose and reduce the size of PDFs? Try the following simple experiment: create a Word file with four RGB photos from a digital camera and half a dozen lines of text. Use Save as PDF from the print dialog, and then check the size of the resulting file. It's likely to be huge - certainly in the tens of megabytes. This is because Save as PDF uses Flate/ZIP compression - a lossless variety - and no optimization. The resulting file is not a lot of use for a Web site. Enter the set of tools on review here. Easy option
Often all you need to do is crunch a PDF down for Web viewing or on-screen reading. PDFshrink Lite will handle this. Its user interface is drag-&-drop, and only three size reduction preferences are offered: five levels of JPEG quality, the downsampling of images to 72dpi, and removal of the Base 14 fonts. Black-&-white images are always output at 200dpi using CCITT Group 4 lossless compression. Our 32MB Word-generated PDF came down to between 76K and 216K. PdfCompress is a similar animal. It offers 11 levels of JPEG quality, optional downsampling to 72dpi, and the removal of the Base 14 fonts. Black-&-white images are handled the same way as in PDFshrink Lite. The one difference is its Allow JPEG recompression feature, although reJPEGing a file seriously reduces the quality. Again, the same Word-generated PDF reduced to between 92K and 336K. However, removing fonts from certain files led to font corruption in Acrobat. The full version of PDFshrink goes a lot further by allowing the use of configurations in a similar way to Distiller presets. Four are pre-created: eBook, Press, Print and Screen. The dialog box for image downsampling is also reminiscent of Distiller with individual settings for colour, greyscale and mono images. The method of downsampling can be selected from average, bicubic and subsample with a dedicated resolution and threshold. Compression types are JPEG or Flate with a quality setting for colour or greyscale, and Flate, Packbits and CCITT Group 3 and 4 lossless compression types for mono. There are also a number of optimization options. Recompressing data using Flate tends to provide a small saving while the removal of duplicate objects makes up for a shortcoming in OS X's Save as PDF facility. This alone can result in a serious file size reduction. Extraneous data such as Adobe Photoshop and Illustrator-specific information, metadata and verbose tagging can be removed, as can PDF thumbnails. A series of hot folders can be set up to handle a PDF workflow scenario too. Shrink-wrapped
As PDF Enhancer shares the same publisher as PDFshrink, it isn't surprising to find a very similar user interface but with a number of additional features. The five pre-created configurations immediately show this with two that are print-related (High Quality Printing and Office Printing), two that are screen related (Screen and Screen with Metadata), and Web. One main feature is Targeted Optimization, which calculates the most efficient way of reducing file sizes. It includes the ability to remove OPI elements, job tickets and edit data, and to clean up form fields and annotations. Even the opening characteristics of a file can be set. What it lacks is the ability to change colour space from RGB to CMYK - quite a serious failing for an ?enhancer'. PDF Enhancer Pro has a few extra features. Fast Web View, where pages can be viewed as they are being downloaded, can be enabled, security and encryption level set, PDFs merged, and the hot folder system set up for PDF workflow.
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