Why does Calibre downscale covers?

[jackm8]

Is it possible to use original cover.jpg file from .epub to be used in Calibre?

Whenever I import books, Calibre generates it's own cover from the one present in .epub file, and it's of lower resolution and lower .jpeg quality compared to the one present in the files. If I go and manually overwrite cover.jpg file that's generated in Calibre Library folder, Calibre then displays full resolution file without problems, so I'm guessing that program downscales covers automatically on import.

[kovidgoyal]

Preferences->tweaks->maximum cover size

[jackm8]

Thanks, I put some silly 9000x9000 number in that and that apparently does it.

[Quoth]

Originally Posted by jackm8

Thanks, I put some silly 9000x9000 number in that and that apparently does it.

The large covers are for Website preview on big screens. They make no sense at all on apps or ereaders. Setting to 1600 x 1200 is generous.
Some ereaders won't even display the cover if it's too large.
A larger cover can take more storage than the ebook!

[JSWolf]

Originally Posted by Quoth

The large covers are for Website preview on big screens. They make no sense at all on apps or ereaders. Setting to 1600 x 1200 is generous.
Some ereaders won't even display the cover if it's too large.
A larger cover can take more storage than the ebook!

That's a rather low number. The Libra 2 has a resolution of 1264 x 1680. What I do is try to find a cover with a higher resolution and reduce it to 1600 lines. I also give the cover a 70% lossless compression. That works perfectly well. This is done in calibre's editor. I may start reducing to 1680

[Quoth]

Originally Posted by JSWolf

That's a rather low number. The Libra 2 has a resolution of 1264 x 1680. What I do is try to find a cover with a higher resolution and reduce it to 1600 lines. I also give the cover a 70% lossless compression. That works perfectly well. This is done in calibre's editor. I may start reducing to 1680

It depends which is more important? The cover or the content.

I read on a Sage (1440 x 1920?) and without a cover, so I see the the sleep screen, which has "Sleeping" etc, so image doesn't fill the screen. I mostly use 1072 x 1430 in calibre because that's my compromise choice. The eink only displays the 16 M shade/colour image in 16 levels of mono anyway, though I do use the colour.

People can set the cover image default to what ever they want and I was only giving a general example while remarking that 9000 x 9000 is a bit high as it's 243 Mbytes when uncompressed!

The 1200 x 1600 is 5.76 M Byte uncompressed.

That's a rather low number. The Libra 2 has a resolution of 1264 x 1680. What I do is try to find a cover with a higher resolution and reduce it to 1600 lines.

So you do exactly what I was suggesting.

[jackm8]

Originally Posted by Quoth

The large covers are for Website preview on big screens. They make no sense at all on apps or ereaders. Setting to 1600 x 1200 is generous.
Some ereaders won't even display the cover if it's too large.
A larger cover can take more storage than the ebook!

Setting it to 9000x9000 doesn't upscaling covers to 9000x9000, it's just keeping resolution of covers as they are. By default, covers that exceed certain threshold get downscaled, and that can have problems when converting files.

[DNSB]

Originally Posted by jackm8

Setting it to 9000x9000 doesn't upscaling covers to 9000x9000, it's just keeping resolution of covers as they are. By default, covers that exceed certain threshold get downscaled, and that can have problems when converting files.

For me, I keep my covers at 1000/1125 x 1500. I recently picked up a 4 book series which has lovely 2400x3600 cover and title page images. The cover images ranged from 1.2MB to 1.4MB, the title page images were from 800KB to 1000KB. Resizing both of them to 1000x1500 dropped the size of the 3 epubs by an average of 1.4MB or to an average size of 1.23MB per book.

[JSWolf]

Originally Posted by jackm8

Setting it to 9000x9000 doesn't upscaling covers to 9000x9000, it's just keeping resolution of covers as they are. By default, covers that exceed certain threshold get downscaled, and that can have problems when converting files.

Setting covers to 9000x9000 means that any covers over that size will not be downloaded. It has nothing to do with changing the size of the cover.

What you may need to do is go to Common options > Page setup. Set the Output profile to Tablet and the Input profile to Default profile. That will keep your covers from being changed.