MobileRead Forums - View Single Post - Full-screen cover when sleeping with ePub?

davidfor · 01-19-2022, 06:23 AM

Sorry, but none of that is correct. If anything, it is backwards. In fact, the cover image for an epub always fills the screen. The problem you are seeing is not where you think it is. The issue is how the cover images are generated for each format.

For sideload kepubs, the image to be used as a cover is marked in the OPF. The device will extract the image and resize it as needed. It does not change the aspect ratio. That means when it is displayed on the sleep screen, it is shown with with borders unless the cover is the same aspect ratio as the screen. For purchased books, the covers are downloaded from the Kobo server but otherwise treated the same.

For epubs, the device renders the start of the book and takes the first page as the cover. That means that whatever you see as the first page when you open the epub will be the cover image. And that includes whatever letterboxing or stretching is done to any image in the page. It also means that if the first page is just text, then the cover image used will be that text.

The above is the reason I say that the information you have is wrong. Unless the image in the kepub has the same aspect ratio as the screen, you will have borders. And for epubs, the borders are not added to the cover image when it is displayed, but, they are in the book.

The fix for epubs is to change the code on the page that displays the cover to fill the screen. This will probably mean the image will be distorted as it will probably have to be stretched to fill the screen. How to do this depends on what tools you use for ebooks and your familiarity with the code in them.

For kepubs, you would need to resize the image to the aspect ratio of the screen before putting it in the cover. Again, this will result in a distorted image.

Alternatively, if you are a calibre user, you can have calibre generate and send the covers to the device when sending the books. There driver has options to do this. For books already on the device, you can use my Kobo Utilities plugin to replace the covers.

There may be a patch to force the device to do this, at least for kepubs, but, I don't remember seeing one.

01-19-2022, 06:23 AM	#2
davidfor Grand Sorcerer Posts: 24,905 Karma: 47303824 Join Date: Jul 2011 Location: Sydney, Australia Device: Kobo:Touch,Glo, AuraH2O, GloHD,AuraONE, ClaraHD, Libra H2O; tolinoepos	Sorry, but none of that is correct. If anything, it is backwards. In fact, the cover image for an epub always fills the screen. The problem you are seeing is not where you think it is. The issue is how the cover images are generated for each format. For sideload kepubs, the image to be used as a cover is marked in the OPF. The device will extract the image and resize it as needed. It does not change the aspect ratio. That means when it is displayed on the sleep screen, it is shown with with borders unless the cover is the same aspect ratio as the screen. For purchased books, the covers are downloaded from the Kobo server but otherwise treated the same. For epubs, the device renders the start of the book and takes the first page as the cover. That means that whatever you see as the first page when you open the epub will be the cover image. And that includes whatever letterboxing or stretching is done to any image in the page. It also means that if the first page is just text, then the cover image used will be that text. The above is the reason I say that the information you have is wrong. Unless the image in the kepub has the same aspect ratio as the screen, you will have borders. And for epubs, the borders are not added to the cover image when it is displayed, but, they are in the book. The fix for epubs is to change the code on the page that displays the cover to fill the screen. This will probably mean the image will be distorted as it will probably have to be stretched to fill the screen. How to do this depends on what tools you use for ebooks and your familiarity with the code in them. For kepubs, you would need to resize the image to the aspect ratio of the screen before putting it in the cover. Again, this will result in a distorted image. Alternatively, if you are a calibre user, you can have calibre generate and send the covers to the device when sending the books. There driver has options to do this. For books already on the device, you can use my Kobo Utilities plugin to replace the covers. There may be a patch to force the device to do this, at least for kepubs, but, I don't remember seeing one.