It seems like a lot of folks are struggling with the size of scanned PDFs. Below are excerpts from two emails I received recently:
My [Fujitsu] ScanSnap makes PDFs that are too big . . . like around 60K per page! What can I do to make these smaller in Acrobat?
I have to eFile [with the Federal Court] and am having to split the filings into many segments to go through the [Court] gateway. The issue seems to be with documents that are scanned on our network scanner. PDFs produced directly from Word are a lot smaller. Is there some trick to reduce the size of scanned files?
Before covering how to reduce the size of scanned documents in detail, let’s discuss four factors that affect the size of scanned images:
- Scanning Resolution
A scan at 600 dpi results in a much larger file than at 300 dpi.
- Color Space
Color and grayscale files result in much larger files than black and white files.
- Physical dimensions of the scanned page
A legal-size scan will be larger than a letter-size scan, with all other factors being equal.
- Compression
Raw scan data can be compressed to make it smaller.
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Compression Types
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Lossless compression retains the exact appearance of the original.
Two common types of lossless compression are ZIP and CCITT Group 4.
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Lossy compression makes some (hopefully) non-noticeable visual trade-offs to further reduce file size.
JPEG is a common lossy compression method.
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Ideally, you would control all of the above factors yourself by scanning at 300 dpi, black and white and using an efficient compression algorithm.
Unfortunately, you many not have that option. Many desktop and network scanners offer limited or confusing options— or— the scanned PDFs arrived from outside your firm.
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Legal Scanning Recommendations
In almost all situations, scan at 300 dpi, black and white.
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For the purpose of this article we will make a couple of assumptions:
- You have a black and white scanned document of unknown dpi and compression
- You have already OCR’d the document, or don’t need OCR
Read on to learn how to reduce the file size of scanned documents using Acrobat.
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