Mobileread
KOReader renders covers unscaled
#1  gogu1904 05-19-2019, 03:29 AM
Hello,

I am using KOReader on Kobo A1 LE. It reads epubs generated with Calibre. The covers are not scaled to the full size of the display, but displayed at their own size, aligned to top and centered horizontally. This is not a problem of Calibre. Do I need to fine-tune KOReader in any way?

Thank you for any feedback.
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#2  NiLuJe 05-19-2019, 03:38 AM
Which covers, where? What's the actual resolution of the image in question in that specific context?

IIRC, CRe will not upscale images, or something...
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#3  gogu1904 05-19-2019, 04:12 AM
Sorry for being opaque.

Epub cover image, size 600x800, generated via default Calibre procedure, rendered when opening the book with KOReader.
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#4  Ken Maltby 05-19-2019, 10:37 AM
There is a setting to "Stretch covers and images to fit screen" in the "Screensaver" > "Settings" menu, on the File Browser menu under the Gear Icon.

Calibre also has a Page Layout menu that lets you set its handling of the covers & images to match your device.

Luck;
Ken

EDIT: The "Screensaver" is where most people encounter the full size "cover" image, that is with the default "Use last book's cover as screensaver" setting. If you were talking about the results of a long press on an image; it's the default to scale the image to "fullscreen" (there is a row of buttons on the bottom for some options as well as the image)
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#5  NiLuJe 05-19-2019, 11:21 AM
600x800 is *far* lower than the KA1's own resolution (which is something like 1404x1872 or something, IIRC).

The usual recommendation is to set your output profile to "Tablet", so at the very least Calibre won't mangle covers/images down to a ridiculous legacy resolution like that if the source is good enough .

EDIT: Note that the Screensaver setting mentioned by @Ken Maltby specifically only concerns, well, screensaver handling, not inline covers/images .
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#6  homeceo43 05-19-2019, 10:36 PM
Quote gogu1904
Hello,

I am using KOReader on Kobo A1 LE. It reads epubs generated with Calibre. The covers are not scaled to the full size of the display, but displayed at their own size, aligned to top and centered horizontally. This is not a problem of Calibre. Do I need to fine-tune KOReader in any way?

Thank you for any feedback.
Are you referring to the first page of the epub that shows the cover?

Mine were small and centered horizontally until I changed the Zoom (dpi) from 96 (which is the default I think) to 300. Now the first page cover fills most of the screen.

This also made other images in the epub larger as well.
first page cover.png 
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#7  gogu1904 05-20-2019, 06:32 AM
Yes, thank you. This did it indeed!
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#8  NiLuJe 05-21-2019, 12:27 AM
Just double-checked that, as per my original comments, I'm not seeing anything obviously wrong when the source is in a proper resolution (i.e.,: high, thanks to the Tablet output profile).
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#9  gogu1904 05-22-2019, 04:28 AM
Yes, if the source is in high resolution and worked with the tablet profile all is all right.

I aimed at saving extra juice from an unneeded large size cover. I am using the standard cover feature to create text only, black on white, metadata cover, with the authors, title, series nicely formatted. For this, a 600x800 resolution is perfect. A 1400x1800 file adds about 50k to 100k to the final size of the file.

Thank you all for your help.
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#10  NiLuJe 05-22-2019, 08:55 AM
You're likely eating more juice upscaling an image than rendering a higher-resolution one without scaling, FWIW .

That's verging on extremely counter-productive premature optimization territory .

In this case, the difference probably basically falls into the "noise" bin anyway, so, eh.
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