Minor improvements to ImageMagick thumbnail filters #8850
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Minor improvements to logging and generation of PDF thumbnails by using a MIFF intermediate instead of a JPEG. Backported from DSpace 7.6. See: DSpace#8850
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Instead of logging the name of the source bitstream, we should be logging the name of the actual thumbnail bitstream that is being considered for replacement. For example, instead of this: IM Thumbnail manual.pdf matches pattern and is replaceable. ... the message should read: IM Thumbnail manual.pdf.jpg matches pattern and is replaceable. This message is already confusing enough, but this will help.
Minor standardization to logging (unneccessary capitalization and excessive spaces).
There is no point passing a page parameter here, with a default of 0 no less, because we will *always* use the first page of the PDF to generate the thumbnail. No other filters use this function and the page parameter is not configurable so we should just hard code it.
Add some comments to document the functionality of the ImageMagick thumbnail filters. This will help others understand it later when we need to re-factor them.
When filtering PDF bitstreams, the ImageMagickThumbnailFilter first creates an intermediate JPEG and then a "thumbnail" JPEG. These two operations are both lossy. The ImageMagick usage guide warns against doing that: > JPEG losses (sic) information, degrading images when saved. > Use some other format for intermediate images during processing. > Only use JPEG format, for the final image, not for further processing. As our current filter architecture requires writing a temporary file we must choose one of the following lossless formats to use for the intermediate: PNG, TIFF, or MIFF. MIFF is ImageMagick's own internal format and is much faster to write than PNG. By eliminating the first lossy conversion we gain 1.1% points on the ssimulacra2 (v2.1) scoring scale of visual quality. See: https://imagemagick.org/Usage/formats/#jpg
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Description
Minor documentation and logging fixes to the ImageMagick thumbnail filters—these are not documented very well and have some logical errors. Also includes a minor optimization for PDF thumbnail generation, which changes the intermediate temp file format to MIFF instead of JPEG so we don't lose quality.
In the long term we will have to re-factor these filters, but for now I want to address some minor issues.
Instructions for Reviewers
Test running the filter-media script on an item with PDF bitstreams. Use verbose and force to make sure the process works as expected:
$ dspace filter-media -i 10568/130406 -v -fList of changes in this PR:
getImageFile()by removing thepageparameter (we always use page 0 and this is not configurable so there is no need to use this parameter)See the commit messages for more information.
Checklist
pom.xml), I've made sure their licenses align with the DSpace BSD License based on the Licensing of Contributions documentation.