PDF Compression

Posted on February 1, 2014January 31, 2014 by Evan Chen (陳誼廷)

I always scan copies of letters into my computer before I send them out. So I had a bunch of large PDF’s sitting around hogging my Dropbox space.

One day I found this blog post which claimed that simply running (in Bash) the commands
$ pdf2ps original.pdf temp.ps $ ps2pdf temp.ps new.pdf
would decrease the file size. (The two commands are part of GhostScript, which I had installed on my Linux boxes anyways.) I couldn’t resist trying it — and miraculously, it worked. It generally decreases my scans by a factor of 10 (from 20MB to 2MB or so).

I have no clue why this works, although it probably has something to do with the fact that the PDF’s are scanned pages . Anyone care to enlighten me?

Published by Evan Chen (陳誼廷)

I am a math olympiad coach and a PhD student at MIT. View all posts by Evan Chen (陳誼廷)

4 thoughts on “PDF Compression”

Tanishq Aggarwal July 24, 20146:44 PM Reply

Perhaps some sort of unnoticeable quality loss occurred?

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1. Evan Chen (陳誼廷) July 27, 20143:04 PM Reply
  
  Probably. But it’s hard to care if it’s unnoticeable :)
  
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  1. Tanishq Aggarwal July 30, 20146:48 AM
    
    Oh there’s also the issue of layering. PDF’s generated by TeX have many layers to them; using these conversions flattened the PDF’s layers, maybe?
    
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  2. Evan Chen (陳誼廷) July 30, 20149:06 AM
    
    Up to now I’ve been doing this with scans from my scanner, not TeX-generated PDF’s.
    
    Though I just tried it with a randomly selected LaTeX PDF (actually my write-up to IMO6) and got a factor of 2 as well. Not that compression is something I’d usually need with a text PDF.
    
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