Turning big scores into small, fast PDF files with Fax Group 4 data compression

Posted: November 9, 2012 in forScore, iPad, scanning, sheet music, tablet

Credit: hp.com

This is a follow-on to my earlier post, When smaller means slower: performance of Acrobat-optimized PDF files in forScore, which is about how certain PDF data compression options can slow down the loading and page-turning of your PDF music score files, even though they shrink the file size.

My singer colleague Steve R. shared some helpful information for making PDF scores small AND fast.  He is in the process of scanning a 175-page vocal score of a large-scale choral work.  That’s a lot of pages, so he needs a way to shrink it down to a small file that will load up quickly on an iPad or other tablet and not be sluggish and unusable in rehearsal and performance.  One of his steps is to scan the score in black-and-white at 200 dpi resolution.

The other step is to use an option known as Fax Group 4 data compression, or G4.  Here are some technical details about G4:

  • G4 is a data compression method originally designed for older fax machines with limited computing power.  That’s why it works so well on today’s tablets – it requires minimal computing power to decompress the file, which keeps it from slowing down the tablet.
  • G4 is optimized for black-and-white images.
  • G4 is lossless, meaning that it will shrink the file without degrading the image quality.
  • Steve tried all of the data compression options available with his scanning tools, and G4 yielded the smallest file.

I’m not sure what hardware or software Steve used to access the G4 option (Steve, maybe you can fill us in?). [UPDATE 11/9/12: @Lorskyfink reports: “I noticed that Acrobat Pro’s “Save As…Optimized PDF” has the option of using CCITT 4 for the monochrome images.”  (CCITT 4 is a type of G4 encoding.)]

And thanks, Steve, for sharing your findings with us!

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  1. Steve Roth says:

    The short version is that I use ImageMagick to do the image manipulation (including compression) and PDF conversion. I’ve sent Tech4Singers full details to post.

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