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I have many old scanned PDFs which take up too much space on disk.

I have tried many PDF compressors available on the web. All of them ask me what compression to use for color images, and what to use for monochromatic images; but I could not find anything to convert EVERYTHING to a binary image.

By binary, I mean that each pixel can only have one of 2 color values: full black or full white. I know that all my PDFs have black/white text (not even grayscale). Can some tool (windows or linux or android) use this knowledge to achieve better compression?

I'm not sure, but "Optimize PDF" tool in Adobe Acrobat Pro may do what I want. However, even if it does, I would prefer to know about a less expensive and a more compact application.

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You can try to compress them with djvu algorythms and collect into one DJVU-file instead of PDF. –  Eddy_Em Apr 6 at 5:34

1 Answer 1

jbig2 compression is the best way to reducing filesize

Adam Langley wrote jbig2enc encoder originally for googlebooks

and then released the source code so anyone can build

you can off course also use a precompiled binary from:

Jbig2enc+ akrykukov patch

the common syntax for jbig2enc is (assuming your files are tiff)

jbig2 -s -p -v *.tiff && pdf.py output >out.pdf

but, for Jbig2enc+ akrykukov patch

jbig2 -s -p -v -P (number of pages for dictionary) *.tiff && thessalonica-pdf.py *.jbig2 >out.pdf

IMPORTANT:

you need python libs to be able to collect and put together all jbig2 resulting files in a pdf

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