Book Covers - how generated? where stored?

[pssquirrel]

I'm trying to understand how Kindles handle book covers.

I've found that when I drag-and-drop an AZW3 directly from my computer to Kindle, I get a generic cover on the Kindle homescreen when browsing in cover view. But when I use Calibre to transfer the AZW3 to my Kindle, the appropriate cover appears on the homescreen.

I also understand that page numbers are stored in a totally separate file (apnx).

Is the cover also stored in the apnx file? or another external file? What does Calibre do when it transfers the AZW3 that is different from a straight drag-and-drop?

I am mystified as I've never had this issue with epubs. Thanks for any insights!

[susan_cassidy]

Book covers are embedded in the book's file. Calibre knows how to convert and keep the original cover. I don't know where your azw3 files are coming from. If from Amazon, they should have covers.

[pssquirrel]

I confirmed the book cover is embedded in the AZW3 because I can navigate to it when I open the book. But it doesn't appear on the homescreen in cover view when I transfer the AZW3 via straight drag-and-drop. It only works if I transfer it via Calibre "send to device."

What does Calibre do during the transfer that's different from straight drag-and-drop? Does it add a necessary external file (like the apnx?) that the Kindle needs to generate a cover on the homescreen?

Thank you.

[Doitsu]

On an eInk Kindle, book covers are stored in the hidden /system/thumbnails folder on the Kindle. I. e. if you manually transfer books that have an ASIN, you'll get the generic cover unless you copy the corresponding thumbnail image. (Calibre does this automatically.)

The thumbnail file name must contain the ASIN number. For example:

thumbnail_B01234567_EBOK_portrait.jpg

[HarryT]

I'd just stick to loading your content with Calibre. Much easier.

[pssquirrel]

Originally Posted by Doitsu

On an eInk Kindle, book covers are stored in the hidden /system/thumbnails folder on the Kindle. I. e. if you manually transfer books that have an ASIN, you'll get the generic cover unless you copy the corresponding thumbnail image. (Calibre does this automatically.)

Doitsu! This is exactly what I wanted to learn.

P.S. to HarryT, I know this is impractical and using Calibre is much easier. I just wanted to understand how the Kindle and AZW3 files work.

[Anthem]

Originally Posted by pssquirrel

just wanted to understand how the Kindle and AZW3 files work.

Nothing wrong with that! I find myself digging around through things like that as well just to see how it is all bolted together.

[pssquirrel]

Yes! I've learned a lot taking apart epubs. Was hoping to do the same with azw3 now that I have a Kindle, but I'm finding azw3 less accessible, harder to understand

[Doitsu]

Originally Posted by pssquirrel

Yes! I've learned a lot taking apart epubs. Was hoping to do the same with azw3 now that I have a Kindle, but I'm finding azw3 less accessible, harder to understand

Have you already checked out KindleUnpack or the KindleUnpack Calibre plugin?

There's also an experimental Sigil epub plugin, that will import azw3 files on the fly (KindleImport) and a plugin that will generate a new azw3 file from an ePub (KindleGen).

BTW, azw3 files support pretty much all epub features and even some features that regular epubs don't support.

[pssquirrel]

Thanks for all the links, Doitsu! I've played around with converting epub to azw3 using Kindle Previewer, and I've exploded a few azw3s with the KindleUnpack Calibre plug-in. I was happy to find that I recognized all the parts of an exploded azw3. I'll check out the Sigil plug-in.

Here's what I'm trying to learn:

1. I know that epubs are just a collection of text/html files compressed into a slightly modified zip file. I like that you can unzip them using standard/generic software, edit with any text editor, then rezip them. From my understanding, it's a lossless process. This plus the fact that it's an open format appeals to me. When you use KindleUnpack to explode an azw3, are the resulting files lossless? Have they been modified or converted in some way, or were they simply decompressed or unwrapped?
   
   
2. After playing around, I discovered that if I insert a valid ASIN in the opf, then use Calibre's Quality Check to "Fix ASIN for Kindle Fire," I can transfer the file via straight drag-and-drop (no Calibre "send to device") and my Voyage will download a cover image from Amazon's servers. (The ASIN doesn't even have to match the metadata in the opf -- if the book is "Alice in Wonderland" and I input the ASIN for Tom Clancy's latest bestseller, I will get the cover for the Tom Clancy bestseller. Also, simply inserting an ASIN in the opf doesn't work; I have to run "Fix ASIN for Kindle Fire" to get a cover.)
   
   What I would like to know is, what does "Fix ASIN for Kindle Fire" do? I dug into some other posts that talked about editing CDEContentType and EXTH 113 & 504, but when I looked in the opf and other exploded files, I found nothing like that. Am I guessing correctly that "Fix ASIN for Kindle Fire" edits hidden files or hidden data not accessible in an exploded azw3? Is there a way to "Fix ASIN" manually?
   
   
3. As far as I can tell, KindleGen/KindlePreviewer is a one-way process where you feed data in and an azw3 comes out, yes? You can't use it to open up an azw3 for editing? If you want to edit, you have to go back to the source data, edit that, and then run it through KindleGen/KindlePreviewer to make a new azw3?

Again, I know it's easiest to just use Calibre. I'm asking because I like to understand these things

Thanks everyone for indulging my curiosity!

[Doitsu]

Originally Posted by pssquirrel

When you use KindleUnpack to explode an azw3, are the resulting files lossless? Have they been modified or converted in some way, or were they simply decompressed or unwrapped?

It's not a lossless process; style names in stylesheets survive, but file names don't. Also some system files are re-created.

Originally Posted by pssquirrel

what does "Fix ASIN for Kindle Fire" do?

AFAIK, it manipulates the metadata of a mobi/azw3 file; it adds ASIN numbers and changes the ebook type to EBOK.

Originally Posted by pssquirrel

Am I guessing correctly that "Fix ASIN for Kindle Fire" edits hidden files or hidden data not accessible in an exploded azw3?

AFAIK, that's correct. This plugin modifies the binary EXTH metadata of a mobi/azw3 file.

Originally Posted by pssquirrel

Is there a way to "Fix ASIN" manually?

You could theoretically use a Python script to manually change/add the ASIN number.

Originally Posted by pssquirrel

As far as I can tell, KindleGen/KindlePreviewer is a one-way process where you feed data in and an azw3 comes out, yes? You can't use it to open up an azw3 for editing?

That's correct.

Originally Posted by pssquirrel

If you want to edit, you have to go back to the source data, edit that, and then run it through KindleGen/KindlePreviewer to make a new azw3?

That's correct. BTW, KindleGen will generate a hybrid mobi file that contains the old and new formats and the source files by default. (You can generate an AZW3 file directly with Calibre.)

[pssquirrel]

Doitsu! I understand so much better now

(I tried to give you more karma, but MobileRead says I have to spread it around before I can give karma to you again )

[DSpider]

How do you find out the ASIN number for an ebook? Search it on Amazon?

And how do you change the home screen covers for PDF files?

[pssquirrel]

Originally Posted by DSpider

How do you find out the ASIN number for an ebook? Search it on Amazon?

Yes. It's listed in the Product Details section.

And how do you change the home screen covers for PDF files?

Don't know. Sorry.

[HarryT]

Originally Posted by Doitsu

It's not a lossless process; style names in stylesheets survive, but file names don't. Also some system files are re-created.

It's only "lossy" in terms of those identifiers, though; nothing is lost in terms of content or formatting. Ie, if you rebuild the book from the unpacked sources, it will be identical in appearance to the original.