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Old 08-17-2011, 05:00 PM   #1
perdman
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18MB EPUB converts to 40MB Mobi! What can I do to reduce Mobi file size?

Hi everybody, I'm new here on this forum. I design books in Adobe InDesign for print and ebook publishing and have been using Calibre to convert EPUBs to the Mobi format. Usually this goes quite well, but today I converted a very large EPUB, weighing in at 18MB, to MOBI, and the resulting MOBI was 40MB! I even did the conversion several times hoping it would make some difference, but to no avail.

My standard workflow involves exporting the EPUB from InDesign CS5.5 with export tagging enabled for all styles, using a TOC Style to generate the navigation, with no embedded fonts, and no generated CSS. I unzip the EPUB contents and insert my own handwritten CSS file and go through the HTML to double check it. When I'm all done I zip it all back up and run it through a validator, then I use calibre to make a mobi of it. Both the EPUB and Mobi are submitted for final publication (usually along with the final print PDF and sometimes online/interactive PDF as well).

This particular file has 184 JPG/PNG images totaling 19.2 MB uncompressed; the entire uncompressed EPUB folder is 21.7 MB. Whatever is happening during the mobi conversion is adding artificial bulk to the file; I've often seen file size increases when converting to mobi, but never more than doubling of file size. Jumping from 18MB EPUB to 40MB MOBI is a bit ridiculous. Anybody have any idea what I might be able to do to reduce the file size?
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