I have an application written in Python, which uses the ReportLab package for exporting PDF files.
Of course, the application needs to be tested. Among other tests, the PDF export function needs to be tested to ensure that the visual rendering of PDF files did not unexpectedly change.
Since it is possible to create and save an expected-results PDF file using fabricated test data, the above implies the need to compare two PDF files. It turns out that two PDF files created from the same data at two different dates – are different, due to embedded timestamps.
Hence, the need to compare visual renderings of the PDF files. ImageMagick’s convert knows how to convert PDF files into PNG. However, one needs to set the background and remove the alpha channel.
convert knows also to perform bitwise XOR on two image files, but it must be told how to compute the bitwise XOR. This is documented in StackOverflow: Searching for a way to do Bitwise XOR on images.
The script in https://gitlab.com/TDDPirate/compare_pdfs implements all the above.
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