Question re: v7.12 new EPUB cover feature

jackie_w · 07-31-2010, 07:09 PM

Quote:

EPUB metadata: When setting metadata in an EPUB file, if it has a well defined image based cover, update it

I read the above in the What's New - New Features for v7.12. Please could someone elaborate what it means. Thanks.

kovidgoyal · 07-31-2010, 07:12 PM

That means that if the EPUB file has a <meta name="cover"> element pointing to a cover image in jpg or png format that is not encrypted, it will be updated to the cover stored in the calibre database when saving to disk/sending to device.

jackie_w · 07-31-2010, 07:17 PM

Thank you. A reply in 3 minutes by the actual developer. Where else would that happen?

You mean we no longer need to convert to get a better cover? Excellent!

kovidgoyal · 07-31-2010, 07:21 PM

yes provided the original epub has the <meta> element in its OPF file.

jackie_w · 07-31-2010, 07:29 PM

OK, I understand.

jackie_w · 07-31-2010, 07:44 PM

Sorry, I'm back again.

Just tried it and the new cover appears on my reader as stated. However it does not appear to be stretched to fill the screen as it would if I'd done a conversion beforehand.

Is this the expected behaviour?

kovidgoyal · 07-31-2010, 08:06 PM

That will happen if the EPUB uses an SVG cover and the old cover's aspect ratio is different from the new cover.

One of the complexities of updating covers in EPUB.

kovidgoyal · 07-31-2010, 08:16 PM

I can probably change the code to rescale the new cover to match the size of the old cover, that should be fairly safe.

jackie_w · 07-31-2010, 09:14 PM

Good idea. That may make it more symmetrical.

I've been playing around with my epub and I experimented by manually scaling my chosen cover to the exact size of the original. I was a bit puzzled that it still didn't fill the ereader screen.

When I looked closer I think the original cover didn't fill it either. This particular epub had a <meta> element and used SVG with a JPG but its cover was not a colour picture, but one of those inside titlepage covers, i.e. black writing on a white background. So it wasn't obvious where the borders were. My new cover probably covered the exact same area as the original, but at least it was centred this time. So hopefully your proposed tweak will be an improvement.

kovidgoyal · 07-31-2010, 09:19 PM

Actually, thinking about it a little, it shouldn't matter even for SVG covers. IIRC SVG covers use the width and height attributes on an svg:image element and that should cause the new cover to be automatically scaled by the epub renderer. Can you check that with a non white image and let me know.

kovidgoyal · 07-31-2010, 09:26 PM

The reason I dont want to rescale the new cover is that if the new cover is larger than the old, why reduce its quality unneccessarily.

jackie_w · 07-31-2010, 09:29 PM

I'll try and find a few more suitable epubs.

jackie_w · 07-31-2010, 09:56 PM

I'm having trouble laying hands on another epub which uses SVG for cover art. So I found an epub (converted in Calibre a few weeks ago with SVG enabled) whose cover jpg is 446x700. It fills the screen of my reader.

I changed the image in Calibre to a different jpg 331x500. I didn't re-convert. Then I sent to the reader. It still fills the screen, i.e. everything is hunky dory.

Is that a suitable test?

kovidgoyal · 07-31-2010, 09:57 PM

Yes that's good enough.

Note that you can use calibre to simply convert a random .txt file to epub with an SVG cover.

jackie_w · 07-31-2010, 10:06 PM

Yes. I ideally wanted to find a commercial (liberated) epub with a rubbishy cover. I imagine, people often want to update the cover of these without changing anything else.

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07-31-2010, 07:12 PM	#2
kovidgoyal creator of calibre Posts: 43,856 Karma: 22666666 Join Date: Oct 2006 Location: Mumbai, India Device: Various	That means that if the EPUB file has a <meta name="cover"> element pointing to a cover image in jpg or png format that is not encrypted, it will be updated to the cover stored in the calibre database when saving to disk/sending to device.

07-31-2010, 07:17 PM	#3
jackie_w Grand Sorcerer Posts: 6,212 Karma: 16534894 Join Date: Sep 2009 Location: UK Device: Kobo: KA1, ClaraHD, Forma, Libra2, Clara2E. PocketBook: TouchHD3	Thank you. A reply in 3 minutes by the actual developer. Where else would that happen? You mean we no longer need to convert to get a better cover? Excellent!

07-31-2010, 07:21 PM	#4
kovidgoyal creator of calibre Posts: 43,856 Karma: 22666666 Join Date: Oct 2006 Location: Mumbai, India Device: Various	yes provided the original epub has the <meta> element in its OPF file.

07-31-2010, 07:29 PM	#5
jackie_w Grand Sorcerer Posts: 6,212 Karma: 16534894 Join Date: Sep 2009 Location: UK Device: Kobo: KA1, ClaraHD, Forma, Libra2, Clara2E. PocketBook: TouchHD3	OK, I understand.

07-31-2010, 07:44 PM	#6
jackie_w Grand Sorcerer Posts: 6,212 Karma: 16534894 Join Date: Sep 2009 Location: UK Device: Kobo: KA1, ClaraHD, Forma, Libra2, Clara2E. PocketBook: TouchHD3	Sorry, I'm back again. Just tried it and the new cover appears on my reader as stated. However it does not appear to be stretched to fill the screen as it would if I'd done a conversion beforehand. Is this the expected behaviour?

07-31-2010, 08:06 PM	#7
kovidgoyal creator of calibre Posts: 43,856 Karma: 22666666 Join Date: Oct 2006 Location: Mumbai, India Device: Various	That will happen if the EPUB uses an SVG cover and the old cover's aspect ratio is different from the new cover. One of the complexities of updating covers in EPUB.

07-31-2010, 08:16 PM	#8
kovidgoyal creator of calibre Posts: 43,856 Karma: 22666666 Join Date: Oct 2006 Location: Mumbai, India Device: Various	I can probably change the code to rescale the new cover to match the size of the old cover, that should be fairly safe.

07-31-2010, 09:14 PM	#9
jackie_w Grand Sorcerer Posts: 6,212 Karma: 16534894 Join Date: Sep 2009 Location: UK Device: Kobo: KA1, ClaraHD, Forma, Libra2, Clara2E. PocketBook: TouchHD3	Good idea. That may make it more symmetrical. I've been playing around with my epub and I experimented by manually scaling my chosen cover to the exact size of the original. I was a bit puzzled that it still didn't fill the ereader screen. When I looked closer I think the original cover didn't fill it either. This particular epub had a <meta> element and used SVG with a JPG but its cover was not a colour picture, but one of those inside titlepage covers, i.e. black writing on a white background. So it wasn't obvious where the borders were. My new cover probably covered the exact same area as the original, but at least it was centred this time. So hopefully your proposed tweak will be an improvement.

07-31-2010, 09:19 PM	#10
kovidgoyal creator of calibre Posts: 43,856 Karma: 22666666 Join Date: Oct 2006 Location: Mumbai, India Device: Various	Actually, thinking about it a little, it shouldn't matter even for SVG covers. IIRC SVG covers use the width and height attributes on an svg:image element and that should cause the new cover to be automatically scaled by the epub renderer. Can you check that with a non white image and let me know.

07-31-2010, 09:26 PM	#11
kovidgoyal creator of calibre Posts: 43,856 Karma: 22666666 Join Date: Oct 2006 Location: Mumbai, India Device: Various	The reason I dont want to rescale the new cover is that if the new cover is larger than the old, why reduce its quality unneccessarily.

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07-31-2010, 09:29 PM	#12
jackie_w Grand Sorcerer Posts: 6,212 Karma: 16534894 Join Date: Sep 2009 Location: UK Device: Kobo: KA1, ClaraHD, Forma, Libra2, Clara2E. PocketBook: TouchHD3	I'll try and find a few more suitable epubs.

07-31-2010, 09:56 PM	#13
jackie_w Grand Sorcerer Posts: 6,212 Karma: 16534894 Join Date: Sep 2009 Location: UK Device: Kobo: KA1, ClaraHD, Forma, Libra2, Clara2E. PocketBook: TouchHD3	I'm having trouble laying hands on another epub which uses SVG for cover art. So I found an epub (converted in Calibre a few weeks ago with SVG enabled) whose cover jpg is 446x700. It fills the screen of my reader. I changed the image in Calibre to a different jpg 331x500. I didn't re-convert. Then I sent to the reader. It still fills the screen, i.e. everything is hunky dory. Is that a suitable test?

07-31-2010, 09:57 PM	#14
kovidgoyal creator of calibre Posts: 43,856 Karma: 22666666 Join Date: Oct 2006 Location: Mumbai, India Device: Various	Yes that's good enough. Note that you can use calibre to simply convert a random .txt file to epub with an SVG cover.

07-31-2010, 10:06 PM	#15
jackie_w Grand Sorcerer Posts: 6,212 Karma: 16534894 Join Date: Sep 2009 Location: UK Device: Kobo: KA1, ClaraHD, Forma, Libra2, Clara2E. PocketBook: TouchHD3	Yes. I ideally wanted to find a commercial (liberated) epub with a rubbishy cover. I imagine, people often want to update the cover of these without changing anything else.