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I have a PDF created from JPEG images colour scanned from a few pages.

The file size is very large (> 325 MB) and I don't have access to the original scans (I only have the PDF file).

Is there any way I can compress this to say 25~50 MB (or at least below 100 MB) without significant loss of quality?

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marked as duplicate by techie007, Scott, Dennis, Windos, Sathya Mar 13 '13 at 3:24

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You can try using Adobe Acrobat tools to attempt to compress it, but based on the current size, you do understand you won't get much better then what you already have right? Any decrease in the size WILL effect the clarify of the images. –  Ramhound Nov 13 '12 at 3:38
    
Use winzip or other compression utility, see how small it can compress it, this will indicate if there is any more room for compression, unlikely without the original content to re-draft the pdf. –  Moab Nov 13 '12 at 4:19
    
Related: Is there a free way to compress a PDF? –  techie007 Mar 12 '13 at 23:38
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2 Answers

If you can use OCR software on the images to turns them into text then you can shrink the document considerably.

If that fails or if the pages are mostly drawings then all you can do is to reduce the quality of the images. Either with specific tools, or just by taking a screenshot of these few pages, editing them and then printing them to a 'PDF printer').

Since the document is only a few pages this could be done quite quickly. For larger documents this would quickly become a burden.

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it's a scanned book I don't have any other option but to look for a software that will compress it for me :( –  user13267 Nov 13 '12 at 11:24
    
the original scans might still be available on some CD but I will have to look for it. If I can find the original scans would it be possible to make a new pdf file but within 50~100 MB? –  user13267 Nov 13 '12 at 11:25
    
Not without reducing quality or turning the pictures into another smaller format. (e.g. into text). Books often contain a large number of words in the same nice and regular font. That makes it easier for OCR, though you might end up with problems in words where a rn gets replaced by a m. Thus you will need to proofread it. –  Hennes Nov 13 '12 at 17:27
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Try using 7-zip to compress the PDF. The 7z compression method normally produces good results.

To really compress a group of images down you need to have the images stored in BMP format and compress them as a whole group rather than have each one compressed individually. That way they can share the 'dictionary' used for compression. However, this would be quite a lot of effort for a one-off file.

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JPEG images already have lossless compression applied. I'd be surprised if there was a significant gain in compression from 7zipping a PDF file. You'd need to throw away information to get a better compression, which means recompressing (re-quantizing) the JPEG images. –  slhck Nov 13 '12 at 9:27
    
@slhck You're right. I don't think you'll get from 300MB to 30MB compression but you might get something if the compression can use common information over all the images. –  snowdude Nov 13 '12 at 9:34
    
@slhck: "JPEG images already have lossless compression applied." - I thought JPEG was a lossy format! –  Karan Nov 14 '12 at 0:25
    
@Karan Run length entropy coding, to cancel out similar values after the quantization stage. –  slhck Nov 14 '12 at 5:23
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