When smaller means slower: performance of Acrobat-optimized PDF files in forScore

Posted: October 31, 2012 in apps, forScore, iPad, scanning, sheet music

When using PDF files in forScore for iPad (or most other iPad PDF reader apps, for that matter), the conventional wisdom is that the larger the PDF file, the slower the performance of the reader app.  Hence, when scanning a score, we choose the lowest possible resolution with acceptable image quality (for me, that’s 300 dpi), opt for black-and-white instead of grayscale or color, and use various PDF processing tools to reduce the file size further.  (In addition to speeding up the PDF performance, the smaller PDF file size also lets us fit more scores in our iPad, Dropbox account, etc.)

However, one nagging question for me has been whether some (not all) of the options in the Adobe Acrobat optimizer tool for shrinking the file actually make the performance worse – specifically, the options for compressing the data contained in the file.  My theory is that while data compression reduces the PDF file size, it also results in the PDF reader app having to do extra work to decompress the data when displaying the file.  (I haven’t gathered data to test this theory.)

Apparently I’m not alone in my concern, as this Twitter conversation started by @Lorskyfink attests:

Here is the link on Acrobat optimization setting tips that I referenced above.

I contacted the forScore support team to see if they could shed light on this issue, and they graciously provided the following response.  While it’s not a definitive answer, it does provide some useful information and guidance.

[Optimization] really depends on a number of things. iOS tends to be happiest with PDFs produced by the built-in Save as PDF function in the print dialog of Mac OS X, but ultimately that’s because that process will strip out all the extraneous data and flatten down any layers into a single, simple PDF.  (Editor’s note: I wonder if Acrobat’s “Save As…” command, which can help reduce file size, does the same processing as this “Save as PDF” function in Mac OS X?)

That said, not everyone has a Mac and there are other ways to squish files and remove extraneous information from PDFs, but it’s hardly an exact science because PDFs can be created, manipulated, and appended to in so many different ways. Ultimately, most issues in forScore have to do with file size per page and the amount of processing it takes to render an image. Compression could play a part in slowing things down, but so can larger uncompressed files, especially if they originated from 600 dpi scans or contain a lot of vector layers that need to be down-sampled [to fit] the screen.

All this to say that I don’t have an exact answer for you, but my recommendation would be to keep file size low while still minimizing compression. (emphasis mine)

[UPDATE #1 11/9/12: My colleague reports that Fax Group 4 is one data compression option that will shrink a PDF file while still allowing for fast loading and display.]

[UPDATE #2 11/9/12: The maker of Fast PDF Scores reports that part of their tool’s optimization process is to decompress the PDF file, in order to address this issue.]

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