Book cover won't show

[davidfor]

Originally Posted by RonaldP

My biggest confusion was (and remains) that I added the same file to my wife's Kobo, at the same time as I did to mine, and the cover displayed perfectly.

What happens depends on what you did before.

If the book had not been on your wife's device, then it is the first time it had seen the book and it generated covers from the book.

If the book was already on the device, it depends on what had happened on the device. The device generates the cover images as needed. It will generate one of the cover images when you scroll to the page in the book list with the book on it. That will also generate the cover image use when the device is sleeping. When you resend a book to the device using calibre, it will delete the cover images that the device has generated. That will allow the device to regenerate the images when it needs to. But, this is done outside the control of the application (nickel) running on the device. It thinks the image is there and doesn't check. Something else has to happen for the cover image to actually be regenerated.

That means, if the book you replaced was the book you are currently reading, or is on the home screen, nickel thinks it has the cover image but it has disappeared, so a placeholder is used. If you open a few other books, it will push the book off the home screen, and after enough books or time, nickel will decide it needs to reload the information about the book when it needs to display it. And that means the cover images will be regenerated as they do not exist.

Restarting the device forces this to happen as nickel has to reread the database and other information about the book.