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copied!<p>I've used a home-baked script which</p> <ul> <li>converts all pages on two PDFs to bitmaps</li> <li>colors pages of PDF 1 to red-on-white</li> <li>changes white to transparent on pages of PDF 2</li> <li>overlays each page from PDF 2 on top of the corresponding page from PDF 1</li> <li>runs conversion/coloring and overlaying in parallel on multiple cores</li> </ul> <p>Software used:</p> <ul> <li>GhostScript for PDF-to-bitmap conversion</li> <li>ImageMagick for coloring, transparency and overlay</li> <li>inotify for synchronizing parallel processes</li> <li>any PNG-capable image viewer for reviewing the result</li> </ul> <p>Pros:</p> <ul> <li>simple implementation</li> <li>all tools used are open source</li> <li>great for finding small differences in layout</li> </ul> <p>Cons:</p> <ul> <li>the conversion is slow</li> <li>major differences between PDFs (e.g. pagination) result in a mess</li> <li>bitmaps are not zoomable</li> <li>only works well for black-and-white text and diagrams</li> <li>no easy-to-use GUI</li> </ul> <p>I've been looking for a tool which would do the same on PDF/PostScript level.</p> <p>Here's how our script invokes the utilities (note that ImageMagick uses GhostScript behind the scenes to do the PDF->PNG conversion):</p> <pre><code>$ convert -density 150x150 -fill red -opaque black +antialias 1.pdf back%02d.png $ convert -density 150x150 -transparent white +antialias 2.pdf front%02d.png $ composite front01.png back01.png result01.png # do this for all pairs of images </code></pre>

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