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davidfor · 11-23-2012, 08:05 AM

This sounds like it should be in the Kobo forum rather than the calibre. Or at least in the device sub-forum. Until it is moved, I'll answer it here.

I think you already know that the Touch uses the first page of the book as the cover. It generates several different sized images and saves them for use later. When it generates the images depends on the firmware. Pre 2.0.0 generated four sizes when it first sees the book. All the 2.x.x generates them as needed but stores for later use. Unless the book is on the SD card. In that case, it generates the image each time it needs it.

Apart from this, the firmware has had problems. 2.0.0 had a problem where it used the wrong cover for the sleep cover the first time it went to sleep after opening a book. It would use the cover from the previous book. The next time it went to sleep, it would use the cover for the current book.

There is also a problem related the the number of images stored and the FAT32 file system. There is a maximum number of files that can be in a directory on a FAT32 file system. This is reduced if long file names are used. The Kobo devices will tend to have very long file names for the cover images. The number seems to be between 7000 and 8000 images in the directory. Depending on the firmware version, there are between two and four images per book on the device. So, you could hit the problem with about 2000 books on the device. With more than 2500, you definitely will. If this is the problem, I am not sure if a blank cover is used or the simple text cover (see below). But this will also be used in the library list and home screen.

Sometimes, the cover used will be a simple text cover. This will have the title of the book and the book type under it. This is always used for TXT and RTF files but will also be used for other books at times. If the cover image for a book hasn't been generated when it is displayed somewhere, the text cover will flash up and then be replaced by the books cover. Occasionally, this doesn't happen and the text cover stays.

That's the basics for covers. There is more in posts in the Kobo forum. Especially about margins.

But, what is the actual problem? "does not always display the cover of the book (when in sleep mode)" does not actually tell me much. Is it displaying the wrong cover? The Kobo sleep logo? Or something else. And does the first page display correctly when reading the book on the device? Also, what firmware version and calibre version. The latter is probably not important as I doubt this is a calibre problem, but we should know just to be sure.

11-23-2012, 08:05 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	This sounds like it should be in the Kobo forum rather than the calibre. Or at least in the device sub-forum. Until it is moved, I'll answer it here. I think you already know that the Touch uses the first page of the book as the cover. It generates several different sized images and saves them for use later. When it generates the images depends on the firmware. Pre 2.0.0 generated four sizes when it first sees the book. All the 2.x.x generates them as needed but stores for later use. Unless the book is on the SD card. In that case, it generates the image each time it needs it. Apart from this, the firmware has had problems. 2.0.0 had a problem where it used the wrong cover for the sleep cover the first time it went to sleep after opening a book. It would use the cover from the previous book. The next time it went to sleep, it would use the cover for the current book. There is also a problem related the the number of images stored and the FAT32 file system. There is a maximum number of files that can be in a directory on a FAT32 file system. This is reduced if long file names are used. The Kobo devices will tend to have very long file names for the cover images. The number seems to be between 7000 and 8000 images in the directory. Depending on the firmware version, there are between two and four images per book on the device. So, you could hit the problem with about 2000 books on the device. With more than 2500, you definitely will. If this is the problem, I am not sure if a blank cover is used or the simple text cover (see below). But this will also be used in the library list and home screen. Sometimes, the cover used will be a simple text cover. This will have the title of the book and the book type under it. This is always used for TXT and RTF files but will also be used for other books at times. If the cover image for a book hasn't been generated when it is displayed somewhere, the text cover will flash up and then be replaced by the books cover. Occasionally, this doesn't happen and the text cover stays. That's the basics for covers. There is more in posts in the Kobo forum. Especially about margins. But, what is the actual problem? "does not always display the cover of the book (when in sleep mode)" does not actually tell me much. Is it displaying the wrong cover? The Kobo sleep logo? Or something else. And does the first page display correctly when reading the book on the device? Also, what firmware version and calibre version. The latter is probably not important as I doubt this is a calibre problem, but we should know just to be sure.