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https://issues.apache.org/jira/browse/PDFBOX-4952?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17191158#comment-17191158
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Christian Appl commented on PDFBOX-4952:
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*COSWriter subtyping:*
Hmm - I could introduce a common AbstractCOSWriter which would both separate
the implementations and evade code duplication. Will have a look into that on
monday.
*XRefStream:*
Ah yes... That is one of the things I would require feedback on. I had some
issues adapting the preexisting XRefStream to create required Objectstream
entries and introduced some subclasses and abstractions for the different entry
types. It does work, but maybe I overstepped when implementing this. I like the
new version better, but would understand if such changes are not welcome.
*"Why is the document larger than before?"*
Same here, the motivation to implement this, is of course, that we would
require something like this on our end.
> PDF compression - object stream creation
> ----------------------------------------
>
> Key: PDFBOX-4952
> URL: https://issues.apache.org/jira/browse/PDFBOX-4952
> Project: PDFBox
> Issue Type: New Feature
> Components: PDModel
> Affects Versions: 2.0.21
> Reporter: Christian Appl
> Priority: Major
>
> I implemented a basic starting point to realize a PDF compression based on
> PDFBox 2.0.22-SNAPSHOT
> I want to use this ticket, to ask if you would be interested in such a
> feature and whether you would be interested to merge it into PDFBox.
> This is sort of a POC, only implementing some very basic functionality, that
> surely must and could be extended further and it does only implement some
> very basic and simplistic Unit Tests.
> However it is able to reduce the size of resulting documents, and creates
> objectstreams as defined in the PDF reference manual.
> *What it currently does:*
> It provides the bundling and compression of objects to objectstreams and
> further applies simple content compression to a small selection of contents.
> To realize content compression, it provides a simple interface and abstract
> class for "ContentCompressor"s which search a document for specific content,
> that could be compressed and do compress that contents.
> Currently two content compressors exist:
> _ImageCompressor_
> Searches for simple images, that could be compressed using DCT.
> _UnencodedStreamCompressor_
> Searches the document for yet unencoded streams and applies a Flate
> compression where necessary.
> Both compressors can be parameterized using a centralized
> "CompressParameters" instance which is passed to a new "saveCompressed"
> method of PDDocument.
> The compression is based on, modifies and is realized by a set of extensions
> for the "COSWriter" class. Basically it organizes objects, that are passed to
> the COSWriter in objectStreams and applies content optimization where
> necessary and possible.
> Currently this does support encryption, but does not support linearization of
> the compressed documents.
> *Caveat:*
> If this feature is interesting to you, then I would not expect you to simply
> merge this fork into 2.0.22. I am expecting that you would like to have some
> details and concepts changed and am ready to implement changes that would be
> required for this to work to your liking.
> *POC:*
> 4 resulting documents can be found in "target/test-output/compression" when
> "COSDocumentCompressionTest" is run.
> *The Pull request can be found on Github at:*
> [https://github.com/apache/pdfbox/pull/86]
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