On a recent visit to my alma mater for some Acrobat workshops I was giving, a member of the campus’ own training team asked me how to get smaller file sizes for their scanned documents when using Acrobat to convert them to image-only PDF’s. They found that the resulting PDF files weren’t that much smaller than the original monochrome (black-and-white) TIFF files. They have a lot of older how-to’s, tutorials and other learning materials that exist as paper. They now need to make them available electronically for anytime access and posterity, and to just get rid of all that paper! When Acrobat 8 was used, the results were the same.
By default, Acrobat uses a compression method called CCITT Group 4 for monochrome images in PDF. This is an old protocol developed for faxing, but works in Acrobat and Acrobat Reader 3.0 and higher. However, a newer compression method has been available since Acrobat 5.0 for monochrome images such as blank-and-white scans. It’s called JBIG2 (Joint Bi-level Image Experts Group) and offers compression orders-of-magnitude greater than can be achieved with CCITT G4. It supports both lossless compression (a la ZIP) and lossy compression (a la JPEG), the latter resulting in even smaller file sizes but at a cost of possible reduction in the quality of image.
However, it’s not enabled in the default Acrobat preferences for conversion to PDF. Here’s how you can change that.
- Choose Edit > Preferences… (Windows) or Acrobat > Preferences… (Mac).
- Select the "Convert to PDF" category on the left to open the conversion preferences.
- From the list of file formats that your version of Acrobat can convert to PDF "directly", choose TIFF. The current settings for conversion from TIFF to PDF are listed to the right. If your list shows "Monochrome Compression: CCITT G4" then click the "Edit Settings…" button.
- In the Adobe PDF Settings dialog box that opens, change the Monochrome Compression setting from "CCITT G4" to "JBIG2 (Lossless)" or "JBIG2 (Lossy)". Again, the latter will give the smallest file sizes but slightly reduce the quality of the scanned image. Click OK.
- Click OK to close the Preferences dialog box.
Now when you open a TIFF file in Acrobat (for example, choose File > Create PDF > From File…) the resulting PDF will be using JBIG2 compression. Save the PDF file, compare it to the original TIFF files, and you should see that they are taking up significantly less space. When we tried this with the training team’s scans and JBIG2 (Lossy) compression, we saw PDF file sizes a quarter of what they originally were as TIFF. If only ROI was measured in bits and bytes!
Note that when you create a PDF file from a scanner, JBIG2 is now used as the default compression method.
There are other ways you can optimize your scanned documents, whether you scan them ahead of time, directly in to PDF with Acrobat and when running Acrobat’s built-in OCR (Optical Character Recognition). I’ll follow up with those tips for optimization another time.