Quote:
Originally Posted by mgrimace
Hi Davidfor, thanks for looking into it, I've tried a number of different combinations on my KA1. Any 'upload covers' option results in a lower-res screensaver. Specifically, the KT driver, the KTE driver, and/or Kobo Utilities.
Here is an example ( kobo link for preview), I used this book because it's easier to see in the gradients below the "P" of the title:
image 1: cover image inside the book (when I start the book for the first time, not the screensaver)
For reference, the cover image is 1000x1500 in Calibre, and the original file in Calibre is epub, converted to kepub on transfer
image 2: screensaver image of the cover using 'upload covers' option
note, this has the 'keep aspect ratio' option unchecked, but the quality is the same for aspect ratio on/off, and greyscale on/off. It is the same overall effect for the KT/KTE drivers, or manual send cover with Kobo Utilities
When I use polish books on the original epub, then send the book over using the KTE driver, but 'upload covers' off, I get a high quality cover, example:
Image 3: high quality screensaver cover image via polish books
I should clarify, when I use the polish books option, the cover is momentarily blank on the KA1 after sending the book over (≤1s, but noticeable), then it seems to generate the cover.
I have no idea how to change those options, but the cover does show when I open/read the book. In fact, the best version of the cover is when I open the book, because it appears to fill the whole screen, in high quality vs the tall aspect ratio with the black bars on the screensaver.
I get a distinct difference between polish covers + no 'upload covers' option selected in driver (good outcome) vs. 'upload covers' with the driver or koboutilities (bad outcome).
Also, If I select 'upload covers' in the driver or koboutilities after polishing the book I still get the bad outcome. |
I did have a play with this last night and I did find a possible cause for the problem. There is a tweak to set the maximum size of the cover in calibre. This affects the generation of the cover when sending it to the Kobo device. I had this set to something like 1200x1600. What that meant was that when I added a cover to calibre that was larger than this it was automatically resize to this size (smaller cover weren't touched). And when the cover was generated by the driver this was the maximum size it would produce. The cover size for the Aura ONE is 1404x1872. A lot of my covers are between 1400 and 1600 in height, so they get resized a little bit to fix this when sent to the device. These look files look good when viewed on the PC.
This size also affects what gets put into the book by a Polish or any of the other actions that change the cover. So, the covers in the books were the same size and looked the same on the PC as the cover generated and sent by the driver.
The difference must be in how the device treats this. When it needs to extract the cover image from the book and generate it, it appears to be doing a good job with any resizing. But, I'd say when doing the cover display, it is a lot simpler. The resizing done at that time shows a lot more artefacts. My guess is that the device expects the stored cover image to be the right size for the screen, it doesn't do as much processing.
The solution for me was to reset the tweak to the default values. These are 1650x2200. Once I did that, the driver generate cover images the same size as the device. In my quick look at them before going to bed last night, I couldn't see any differences between the cover images generated by calibre and the device. That was viewing them on the device.
To check this, the tweak is called "maximum_cover_size". To access them, open the preferences and select "Tweaks" near the bottom of the screen. Select the tweak in the list on the left to see the value. I simple hit the "Reset Tweak" value to go back to the default. I suspect I set this to a smaller size when using the Glo. It made a bit of sense then, but not as much now.
If this doesn't solve it, then I'd like to look at the actual images generated. Also, I don't see what firmware version you are running. There have been at least two changes in the firmware that could affect this. One probably only affects epubs, but the change to 32bpp processing probably has a wider affect.