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Newly Bloated Sizes of ePub files

Today I received an O'Reilly e-mail saying "As part of our continued efforts to improve the quality of our ebooks, we have recently released updates of the EPUB and Mobi files for the majority of our titles.". I just downloaded new versions of the four ePub titles which I own. I am a little surprised to see that the file sizes have more than doubled. One ePub file even tripled in size. (What was a 853KB file for the bash pocket reference is now a 2556KB file.) Embedding some new fonts in the files should not make that big a difference.

Maybe someone made a mistake when configuring the software to generate ePub files?
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  • Hi Nigel,

    Thanks very much for your feedback. The file size increase in the Bash Pocket Reference EPUB is indeed due to the embedding of additional fonts. To improve rendering on ereaders that support font embedding (such as iBooks and the Sony Reader), we now embed 8 OTF variants of the DejaVu family in our EPUB files:

    DejaVuSansMono-Bold.otf
    DejaVuSansMono-BoldOblique.otf
    DejaVuSansMono-Oblique.otf
    DejaVuSansMono.otf
    DejaVuSerif-Bold.otf
    DejaVuSerif-BoldItalic.otf
    DejaVuSerif-Italic.otf
    DejaVuSerif.otf

    When zipped into an .epub file, these fonts are about 2.2 MB in size, so that's where the extra 1700 KB is coming from.

    As part of our EPUB/MOBI updates, we also increased the quality of the JPEG images that we embed in our ebook files. This also has an effect on the file size, which is why you may have seen file-size increases in books that have many images.

    We're certainly aware that one customer's "improvements" may be another's "bloat". However, the vast majority of the feedback we've received over the past year has been requests to increase image quality and font support. So we made a calculated decision to enhance quality at some cost to file size.

    If we get lots of feedback from customers that they prefer the smaller EPUBs/Mobis, rather than the higher-quality large EPUBs/Mobis, we're more than willing to reevaluate this decision and revise our ebook files accordingly.

    Thanks again for your comments. Please let me know if you have any further questions or concerns.

    Thanks,
    Sanders
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