How to reduce scanned PDF file size on Mac

By | August 19, 2018

Problem: Reducing PDF file size on Mac

I scanned some of my personal documents in PDF format on Mac. The files were big sized for any email attachment and so I started looking for some application or free solution to reduce these PDF documents. The first solution that was readily available on my Macbook was to use Preview.

You can open a PDF document in preview mode and then select File–>Export. In export dialog select Reduce File Size for Quartz Filter and click save. A PDF file will be created by the specified name in export dialog with a minimal file size. However the export is not good for use as it substantially reduce the resolution and hence was not a good solution.

Then I stumbled across another simple and free solution by Jerome Colas. You need to download the below given filters and copy it to the appropriate location as per your OS.

https://github.com/joshcarr/Apple-Quartz-Filters

Copy filters to below given location

  • If you are running Lion or Mountain Lion (OS X 10.7.x or 10.8.x) then you should put the downloaded filters in “Macintosh HD/Library/PDF Services”This folder should already exist and contain files.
  • If you are running an earlier version of OS X (10.6.x or earlier), then you should put the downloaded filters in “Macintosh HD/Library/Filters”.

How to use these filters

  • Open a PDF file using Apple’s Preview app,
  • Choose Export (or Save As if you have on older version of Mac OS X) in the File menu,
  • Choose PDF as a format
  • In the “Quartz Filter” drop-down menu, choose a filter “Reduce to xxx dpi yyy quality”“Reduce to 150 dpi average quality – STANDARD COMPRESSION” is a good trade-off between quality and file size

Screenshots are given below

01-pdf-mac-file-size

Actual File Size

02-pdf-mac-file-size

Enter export as name, select filter from Quartz Filter

03-pdf-mac-file-size

Selected Standard compression 150 dpi

04-pdf-mac-file-size

Actual and reduced file sizes

Here is how it works:

    • These are Quartz filters made with Apple Colorsinc Utility.
  • They do two things:
    • Down sample images contained in a PDF to a target density such as 150 dpi,
    • Enable JPEG compression for those images with a low or medium setting.
  • It works with most of the PDF files however their are exceptions. The details are given below: –
      • It will generally work very well on unoptimized files such as scans made with the OS X scanning utility or PDFs produced via OS X printing dialog.
      • It will not further compress well-optimized (compressed) files and might create bigger files than the originals,
    • For some files it will create larger files than the originals. This can happen in particular when a PDF file contains other optimizations than image compression. There also seems to be a bug (reported to Apple) where in certain circumstances images in the target PDF are not JPEG compressed.

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