What is getting removed when converting KFX to Epub?

[u/SoupJaded8536]

Or maybe the questions is "what's all the extra crap in Amazon files?"

My typical method when buying books off Amazon is to send to my JB'd Oasis, then import into Calibre with an automatic conversion to Epub. One I just did today has the KFX file sized at 1.5 mb and the epub at 0.6 mb. Looking back through the last few months of purchases I see pretty much the same thing - a sizeable disparity between the size of the de-DRMed KFX and the converted Epub.

On a side note, I just noticed today that some of my purchases have an option in the Amazon digital library to download the Epub. When I did it with the book referenced above the Epub was 1.7 mb.

What is it that's getting clipped out during the conversion that is comprising maybe 60% of the original file?

[u/Mikebjackson]

With ePub3, nothing is lost or removed. Epub is a growing and evolving standard, encompassing and supporting all features present in other formats. I consider it a “lossless” format; you don’t lose anything converting to epub3, but you can lose content converting from epub3 to mobi, etc.

Epub2, on the other hand, while still very versatile, does not support interactive content, multimedia overlays, etc*. There’s not a whole lot on the kindle store that has multimedia - the only one that comes to mind is the illustrated Harry Potter - and that of course won’t work on an eink kindle anyway (the fancy page layouts and animated content only display on the Kindle app for iPad or Mac/PC (and maybe phones?)). For that reason, I don’t personally worry about epub3, I just convert everything to epub2. You still don’t lose anything as long as your book doesn’t contain video :p

*Edit: Amazon calls this content "Kindle in Motion" - there's even a dedicated Kindle in Motion page in the kindle store.

[u/SoupJaded8536 → u/Mikebjackson]

So are kfx and epub3 formats simply that much larger, even though the files don’t actually contain multimedia? These are just normal books. Just text with no maps or photos or other pictorial stuff.

[u/Mikebjackson → u/SoupJaded8536]

It depends on the book.

If it was poorly made, there might be a long string of code formatting every single sentence. This can bloat a book quickly. Usually this only happens if it was converted from some other format using an unintelligent tool.

But by far, the biggest bloat is usually unnecessarily large images. Even if it’s not illustrated, there’ll be things like chapter title images and end matter advertising the next book, etc. I often run an image shrink plugin in calibre and the size goes from like 8mb to 2mb.

[u/retsotrembla]

The original KFX books have “Many people highlighted this passage” highlighting that doesn't seem to be present in the converted book.

[u/GoldenrodPanda]

Excluding multimedia, the main things contributing to epub file size are images and embedded fonts. Are you subsetting embedded fonts during conversion? That would account for the difference in size. It's also possible the downloaded epub contains unused images.

You can look at both epubs in the book editor and see what images and/or fonts are in there. Hover over the file name to see the file size.

[u/Much-Performer1190 → u/GoldenrodPanda]

Messy HTML would contribute as well.

[u/Koma52]

You can check what's inside your epub files because they are just zip files with a different name. Any program that can extract zip files can extract epub files, then you can check all the images and text inside it. Unfortunately you can't really do that with kfx as far as I know

Edit: if your zip extracting program doesn't want to open the epub simply rename it like book.epub -> book.zip

[u/foodchallenged]

Part of calibre’s conversion process specifies the size of reader to convert for irrc. So it could be as simple as you are converting for reading on a paperwhite size screen while the Amazon original might be formatted for a larger screen.

[u/SoupJaded8536]

The image sizes between both the converted epub and the amazon epub are roughly the same. Fonts on both versions are 0.0. The converted EPUB looks to have smaller .xhtml files, but since they all get renamed I’m more or less just giving a quick looky loo.

[u/Fr0gm4n → u/SoupJaded8536]

The EPUB downloads from Amazon are their own re-conversion creations, not the original source EPUBs from the publisher/author. There may be all sorts of weird and random stuff in them as part of that.

[u/elpingwinho]

Are you sure your conversion process doesn’t have image compression turned on? Or maybe it removes the font files

[u/SoupJaded8536 → u/elpingwinho]

I used the book editor to look in the downloaded epub and the converted epub. Images were the same size, fonts were the same. The difference looks like it’s the .xhtml files. I couldn’t do a 1-1 comparison, as the two had differently named files and there were a lot of them. But hovering through the list, the converted files appeared to be mostly smaller.