Extras added to epub when sending

[DNSB]

I was noticing that I seemed to be running out of space on my KA1 faster than expected. So I started looking at the files in my Calibre library and on my KA1.

I noticed that the files on the KA1 were between 600K and 1.3MB on the average larger than the files in my Kobo library.

I copied a couple of files back to my PC and found that for some reason, an OEBPS directory containing a copy of the cover image was being created inside the existing OEBPS directory when the file was being sent to the ereader.

I've attach a couple of images showing what 7Zip sees as the contents of the file. The cover image is 649883 bytes which, oddly enough, matches the size of the extra OEBPS directory.

Any suggestions as to why this is happening? Calibre version is 3.3, Windows x64 using the Kobo Touch driver.

[kovidgoyal]

Covers are updated when updating metadata. And metadata is updated when sending files to a device. The original cover will not be replaced if it is not corectly identified as a cover in the opf file of the epub.

[DNSB]

Originally Posted by kovidgoyal

Covers are updated when updating metadata. And metadata is updated when sending files to a device. The original cover will not be replaced if it is not correctly identified as a cover in the opf file of the epub.

Quick question first, is the above correct or should it read "The original cover will not be replaced if it is correctly identified as a cover in the opf file".

As far as I can tell looking at the epubs that I have edited, the covers are correctly identified in epub 3.0 ebooks using:

<item id="cover-image" href="../Images/cover.jpg" media-type="image/jpeg" properties="cover-image"/>

For epub 2.0 ebooks, the boilerplate I use for cover images is two lines:

<item id="cover" href="cover.jpg" media-type="image/jpeg">
<meta name="cover" content="cover"/>

While I could understand this behaviour when a different cover image is being inserted, it seems rather pointless when the inserted cover image is a copy of the existing cover image.

Apart from anything else, adding a OEBPS directory inside an existing OEBPS directory is, to me, a rather odd thing to do.

[kovidgoyal]

calibre does not check if the cover is the same. That would be a waste of resources, with lots of false negatives since cover images are often resized. For instance, they are resized when added to calibre if larger than the max allowed size.

And the sentence is correct. Only if the original cover image can be indentified, can it be replaced. Otherwise, a new cover image is created and marked as the cover.

Although, since you are using a Kobo it might be that the Kobo driver (or kobo extras plugin) does something special for epubs. The way to test that is to use save to disk in calibre and see what happens to the cover in the saved epub.

[DNSB]

Originally Posted by kovidgoyal

calibre does not check if the cover is the same. That would be a waste of resources, with lots of false negatives since cover images are often resized. For instance, they are resized when added to calibre if larger than the max allowed size.

And the sentence is correct. Only if the original cover image can be indentified, can it be replaced. Otherwise, a new cover image is created and marked as the cover.

Although, since you are using a Kobo it might be that the Kobo driver (or kobo extras plugin) does something special for epubs. The way to test that is to use save to disk in calibre and see what happens to the cover in the saved epub.

I'll give save to disk a try and see what happens. As for resizing, I do a manual resize on virtually all cover images when I update the metadata in the Calibre library so that might be part of the issue.

[theducks]

Originally Posted by DNSB

I'll give save to disk a try and see what happens. As for resizing, I do a manual resize on virtually all cover images when I update the metadata in the Calibre library so that might be part of the issue.

You can resize/rotate any image inside the book, using the Calibre Editor.
double click on the image file name in the book browse or the embedded link on the page it is used)

[DNSB]

Originally Posted by theducks

You can resize/rotate any image inside the book, using the Calibre Editor.
double click on the image file name in the book browse or the embedded link on the page it is used)

It's not a matter of editing the image (I use GIMP, Paint.net, etc. to do that), it is that an extra cover image is being added to the epub when it is sent from Calibre to my Kobo. For instance, I sent a 1.45MB epub (of which 740K was the cover image). It arrived on my Kobo weighing in at 2.17MB. That size was checked before I disconnected the Kobo so no processing by the Kobo.

The trigger for noticing this? I have ~2800 ebooks on my KA1. When I looked at the storage statistic, over 1GB more than expected had been consumed. Comparing the size of epubs in the eLibrary folder on the KA1 (where I store sideloaded epubs) to the total size of the epubs in my Calibre_KA1 Calibre library (I copy the books transferred to the KA1 from their home library to the KA1 library to make it easier to recover from a factory reset or decision to do a clean install), I was struck by the fact that the epubs in the eLibrary directory on the Kobo consumed ~1GB more space. Even worse--for me--was that when I opened several of the files in 7Zip,they had an extra OEBPS directory nested in the original OEBPS directory. If I open the modified epub in Sigil, it "corrects" the issue and I end up with cover.jpg and cov0001.jpg in the Images directory.

I really wouldn't care except that the KA1 does not have an external uSD card so I currently show 1.2GB free of 6.7GB total. On my H2O, which has quite a few more books, the total wasted space is about 2.7GB on a 32GB uSD card leaving me with ~15GB free on the uSD card.

[davidfor]

@DNSB: There might be a way to stop this. The ePub Metadata Writer has an option that stops the cover from being added if it can't be identified. It was added a while ago to stop the cover image being added when there is a text only cover in the book. It doesn't stop the cover being updated during a conversion or Polish, but I think it should prevent the extra cover image being added.

[DNSB]

Originally Posted by davidfor

@DNSB: There might be a way to stop this. The ePub Metadata Writer has an option that stops the cover from being added if it can't be identified. It was added a while ago to stop the cover image being added when there is a text only cover in the book. It doesn't stop the cover being updated during a conversion or Polish, but I think it should prevent the extra cover image being added.

Another item to give a try. I take it this is the disable-add-missing-cover in the epub writer plugin?

[davidfor]

Originally Posted by DNSB

Another item to give a try. I take it this is the disable-add-missing-cover in the epub writer plugin?

Yes it is.