Mobileread
Size of mobi much larger than epub?
#1  comet 06-15-2011, 04:33 AM
Hallo,

I buy books at o'reilly, and there I get the same title in different formats. I observed that for one book I bought the epub for my Sony has a size of 4.7MB, the mobi for my kindle 17.1MB! What is the reason of this large difference?
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#2  pdurrant 06-15-2011, 05:41 AM
Quote comet
Hallo,

I buy books at o'reilly, and there I get the same title in different formats. I observed that for one book I bought the epub for my Sony has a size of 4.7MB, the mobi for my kindle 17.1MB! What is the reason of this large difference?
Unpack them both and find out. It's probably due to images, although I don't really see why.

It's also just possible that the Mobi also has a copy of the ePub stuffed at the end of it.

The ePub you can unpack just by unzipping it. The Mobi you'll need the Mobipocket Unpack script from here: http://www.mobileread.com/forums/sho...36&postcount=5
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#3  HarryT 06-15-2011, 06:14 AM
There are two probable reasons:

1. Most Kindle books are created using Amazon's "Kindlegen" tool. This includes a copy of the complete HTML source into the book, which increases the size considerably.

2. ePub files use a much more efficient compression method than Mobipocket format does.

As Paul notes, if the book is illustrated it's possible that the Kindle version has higher-resolution images than the ePub version does.
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#4  dwig 06-15-2011, 07:59 AM
The other thing that can happen occurs when a ePub with inefficient CSS usage is converted to MOBI. If the CSS for, say, the <p> tag contains 40 characters the bulk of that can get moved to each and every <p> tag in the html that is integrated into the MOBI adding bulk to the MOBI.

It more efficient to put the style in a <DIV> that spans all of the matching <P>'s leaving the <P> tags unstyled. This will reduce bloat in the MOBI conversion.

When converting ePub to MOBI with calibre, which doesn't embed the source in the output MOBI, the resulting MOBI files are sometimes slightly smaller, often slightly larger (~10%) and only occasional substantially larger. The latter generally being cases of poor CSS usage.
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#5  bfollowell 06-23-2011, 05:43 AM
Assuming the epub doesn't have large embedded fonts or the like, I've noticed that a typical mobi version of an ebook tends to run anywhere from 10%-25% larger than it's epub cousin. That's just been my experience though. Your mileage may vary.

- Byron
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#6  lenz117 07-09-2011, 02:37 AM
HI there guys - I have a similar and slightly alarming issue:

I have an epub file that at 0.7mb that when converted jumps to 3mb. I have played with calibre 0.8.8 with varying results. I am using optimised gif files.
-
If I do a straight epub -> mobi conversion then the size increases 4 fold.

I just changed the mobi output settings to generic rather than Kindle and this then created a mobi at 1.5mb - but now cant replicate that on other book files (I have 5 I am trying to publish)

I beleive that when you convert to mobi - epub also gets bundled hence some increase in file size - but 4 times?

I know there was a script to remove the epub aspect from a mobi - but the script I have has no effect with these new files.

Has anyone else had any experience of optimising mobi files - naturally to try and reduce delivery charges for books
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#7  pdurrant 07-09-2011, 03:56 AM
Quote lenz117
HI there guys - I have a similar and slightly alarming issue:

I have an epub file that at 0.7mb that when converted jumps to 3mb. I have played with calibre 0.8.8 with varying results. I am using optimised gif files.
-
If I do a straight epub -> mobi conversion then the size increases 4 fold.

I just changed the mobi output settings to generic rather than Kindle and this then created a mobi at 1.5mb - but now cant replicate that on other book files (I have 5 I am trying to publish)

I beleive that when you convert to mobi - epub also gets bundled hence some increase in file size - but 4 times?

I know there was a script to remove the epub aspect from a mobi - but the script I have has no effect with these new files.

Has anyone else had any experience of optimising mobi files - naturally to try and reduce delivery charges for books
If you're converting with Calibre, the ePub does not get added to the end. That's purely if the conversion is done with Kindlegen.

If you want to know where the extra is coming from, unpack the Mobipocket and see. My guess is that Calibre is doing something to the pictures to make them larger (in bytes). But that's only a guess.
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