Book cover image cannot be displayed. about epubreader

[vers-one]

That's interesting. Can you upload your epub file somewhere so I can take a look?

[ilia-valchenko]

@versfx Yes, of course. There are few books which I used. Unfortunately you should download it from google drive because github doesn't support epub extension in attachment. https://drive.google.com/drive/folders/0BwwwPXS7GsatY25xWVRxUmh6TWc?usp=sharing

[ilia-valchenko]

@versfx I found one interesting fact. I looked into few epub archives and found that a book cover image might situated into a different folder (for example OPS\images, OEBPS\images). Some archive doesn't have folder which contains any other images.

[vers-one]

EPUB specification does not define a way to describe covers, but the usual practice is to set it using <meta name="cover" /> tag in the OPF file (as a reference to the cover image file). In addition to that some books also provide an alternative XHTML version of the cover using <item id="cover" media-type="application/xhtml+xml" /> tag (in the manifest section) and/or using <reference type="cover" /> tag (in the guide section), however I haven't seen a book with XHTML cover which didn't have an image version of the cover.

In your case:

• Carroll_Lewis_-_Alice_Adventures_in_Wonderland.epub: has XHTML cover in the reference tag, but there is no image version of the cover specified;
• Chehov_Anton_-_Rasskazy_1887.epub: also XHTML cover in the reference tag, no image version;
• Conan_Doyle_Arthur_-_The_Lost_World.epub: has image version specified as <meta content="item6" name="cover" />, but there is no content element with ID = "item6" in the manifest section below;
• the-doomed-city.epub and zhuk-v-myraveinike.epub: no specified covers.

Pocket Book reader probably takes XHTML versions or renders the first page of the book as a cover.

If you want to get an XHTML version of the cover from the guide section (which again is very unusual for the most of epub files), you can do it like this:

EpubGuideReference coverPageReference = epubBook.Schema.Package.Guide.FirstOrDefault(reference => String.Compare(reference.Type, "cover", StringComparison.OrdinalIgnoreCase) == 0);
if (coverPageReference != null)
{
    EpubTextContentFile coverPage;
    if (epubBook.Content.Html.TryGetValue(coverPageReference.Href, out coverPage))
    {
        // coverPage.Content has XHTML version of the cover page
    }
}

[ilia-valchenko]

@versfx What do you think it's a good idea to search a book's cover across the archive folder and then store it in a database (as array of bytes for example)? Unfortunately a lot of books will have incorrect a book's metadata. I think that change a book's metadata it's not a good idea. I develop the ePUB reader application based on Xamarin.Forms. A default user can't change metadata by itself. Do you have any other elegant ideas how to get a book's cover image. I know that I can display it by using cover.html, but I'm looking for a approach to display a book's preview at my home page. Also I want to say thanks for you informative answers.

[vers-one]

The problem is that you cannot distinguish cover image from other images in the book unless it is explicitly marked as a cover. Of course you can apply some heuristics by looking for an image that has "cover" in its name but this is not very robust solution. Another approach would be to show all the images (epubBook.Content.Images) to the users and ask them to choose the cover.

[vers-one]

Please let me know if you have any other questions or comments.