How to compress a scanned PDF?

[huck999]

I am using Acrobat 9 Standard.

I have a 22 page printed text document (no pictures) on letter sized paper.  I had it scanned to PDF.  It is 24 MB.  I have a scan of a similar document that someone else did.  It is 332 KB (roughly 100 times smaller).  Both are perfectly legible.

I have 2 questions:

1. How can I compress the 24 MB document to make it smaller?
2. Why did I get such huge differences in file size?  And how can I get smaller file sizes from scans.

In my office I have an HP Officejet Pro.  The HP software scans directly to PDF but the file size is large.

[MichaelKazlow]

I do not have Acrobat 9 Standard, but I believe you can use the PDF optimizer to shrink the size of the file. The best way to control the size of the file is at scanning time. You can usually control the dpi (dots per inch). Most scanners try to scan at the highest resolution, usually 200 to 300 dpi is sufficient. If there are no pictures scanning greyscale or B & W will also shrink the size of the file immensely. B&W scanning willl always give you the smallest sized file. Lastly, the most efficient scanning is usually done by scanning to TIFF and importing the TIFF into Acrobat. This will give you the best results for text. Some scanner software will scan to jpg and even if scanning to pdf it will use jpg settings which will give the nice results when there are images, but do a poorer job of keeping the text crisp.

[huck999]

Thanks for the reply.

I could not find PDF optimizer.  How do you find it?  I didn't find any reference to it in the help file either.

[Rakesh_S]

The steps provided as below has been tested on Acrobat X Pro. However as I do not have Acrobat 9 please look for the Optimized PDF option at your end. (NOTE: In Acrobat 9 it might be "Advanced > PDF Optimizer")

1. Go to "File" > "Save as" > "Optimized PDF"

NOTE:

- Now you will be on the PDF Optimizer window as above.

- You can change "Make compatible with" option per your requiremt)

2. Select Settings as "Custom"

NOTE: You will be prompted to "Save current settings as" that you can use to downsample future documents

3. Check mark "Images"

    a. Quality as "Minimum"

NOTE:

- The above settings optimized the 837 KB file size to 410 KB

- You can try to experiment by changind other options as well at your end.

[huck999]

Thanks.  It took quite a while to find Optimize.  Not in File>Save As,  Not in Advanced

Not mentioned in Help

Finally found it in Document>Optimize scanned PDF.

It reduced a 24MB file to about 1.5 MB (depends on what quality I specify).

[Bill12]

The location was changed for AA X and that was your problem. A lot of the problems stem from the default use of 24-bit color by many scanners as well as a high resolution. You can reduce the color depth as well as the resolution to reduce the size. Be sure to use Save As or it will save the old stuff too.

Another option that may require some editing would be to OCR the document. If you do it as a clearscan, it will replace graphic text by an estimate of the text in a font. The editing comes in with the corrections that are generally needed with OCR. The other two forms of OCR do not replace the graphic image, but put the OCR text behind the image -- making the file even larger.

[huck999]

Thanks.  Interesting.

How would you reduce the color depth and/or the resolution?

I didn't see any option for that.

Incidentally, I loaded the images into CorelPhotoPaint (where it would be possible to reduce color depth & resolution) and saved the file with very high compression.  That only brought the size down to 6 MB (vs 1.5 MB with Optimize scanned document).  However, that is an excessive amount of work.

[antonyhill]

I notice the same. If I scan directly through the device to USB (it has such option), then document is for some 7 pages of text in 600dpi around 800kb. Scanning from computer results in bigger and uglier images. I guess reason is twofold. First scanning settings.

Documents from scanner device are much cleaner, I guess there is higher contrast set and perhaps tresholds applied so that text is black and white space on paper is white. Scanning from computer through the same scanner results in subtones in the supposed to be white areas. This makes a big difference IMO for quality of compression later the document is created.

Another thing is the features of the resulting PDF. See more info here:

http://blogs.adobe.com/acrolaw/2009/08/reducing-the-file-size-of-scanned-pdfs/

I guess the scanner (it is actually a MFC device) is using high lossless compression which IMO is perfectly fine for the job. No need for lossless compression for scanned documents.