How to prevent cover being replaced when sending book to device?

GeoffR · 04-09-2015, 04:41 AM

I have an epub with a PNG cover image. When I import the book into Calibre, the cover gets converted to JPG and stored in the Calibre library. Then when I send the book to my device (or save to disk), it seems that Calibre converts its JPG cover into PNG and uses that to replace the original cover in the epub.

This means there is a PNG --> JPG --> PNG conversion taking place for every book with a PNG cover, resulting in a loss of image quality.

How can I prevent Calibre replacing the original PNG cover with the JPG cover kept in the Calibre library?

Alternatively, is there a way to prevent Calibre converting the cover to JPG in the first place?

theducks · 04-09-2015, 11:04 AM

Quote:

Originally Posted by GeoffR

I have an epub with a PNG cover image. When I import the book into Calibre, the cover gets converted to JPG and stored in the Calibre library. Then when I send the book to my device (or save to disk), it seems that Calibre converts its JPG cover into PNG and uses that to replace the original cover in the epub.

This means there is a PNG --> JPG --> PNG conversion taking place for every book with a PNG cover, resulting in a loss of image quality.

How can I prevent Calibre replacing the original PNG cover with the JPG cover kept in the Calibre library?

Alternatively, is there a way to prevent Calibre converting the cover to JPG in the first place?

Tick No Cover in the device driver settings? I don't know if this option removes an existing cover, or just prevents one from being updated/added

eschwartz · 04-09-2015, 05:17 PM

Shouldn't calibre be embedding the JPG???

I don't think there is any way.

@theducks -- where is that option?

theducks · 04-09-2015, 07:55 PM

Quote:

Originally Posted by eschwartz

Shouldn't calibre be embedding the JPG???

I don't think there is any way.

@theducks -- where is that option?

It is an Conversion Output option

kovidgoyal · 04-09-2015, 08:28 PM

covers in calibre are always jpg. JPG->PNG is lossless. PNG->JPG is not. There is no way to prevent calibre from updating covers when ending books, short of disabling the EPUB metadata writer plugin.

GeoffR · 04-11-2015, 05:07 AM

Okay, so the workaround I have found is to edit metadata to remove the cover before sending the book to the device, and then add the cover back and upload the thumbnails with the KoboUtilities plugin. This results in JPG thumbnails but with the original PNG cover inside the book.

04-09-2015, 04:41 AM	#1
GeoffR Wizard Posts: 3,821 Karma: 19162882 Join Date: Nov 2012 Location: Te Riu-a-Māui Device: Kobo Glo	How to prevent cover being replaced when sending book to device? I have an epub with a PNG cover image. When I import the book into Calibre, the cover gets converted to JPG and stored in the Calibre library. Then when I send the book to my device (or save to disk), it seems that Calibre converts its JPG cover into PNG and uses that to replace the original cover in the epub. This means there is a PNG --> JPG --> PNG conversion taking place for every book with a PNG cover, resulting in a loss of image quality. How can I prevent Calibre replacing the original PNG cover with the JPG cover kept in the Calibre library? Alternatively, is there a way to prevent Calibre converting the cover to JPG in the first place?

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04-09-2015, 05:17 PM	#3
eschwartz Ex-Helpdesk Junkie Posts: 19,421 Karma: 85397180 Join Date: Nov 2012 Location: The Beaten Path, USA, Roundworld, This Side of Infinity Device: Kindle Touch fw5.3.7 (Wifi only)	Shouldn't calibre be embedding the JPG??? I don't think there is any way. @theducks -- where is that option?

04-09-2015, 08:28 PM	#5
kovidgoyal creator of calibre Posts: 43,935 Karma: 22669822 Join Date: Oct 2006 Location: Mumbai, India Device: Various	covers in calibre are always jpg. JPG->PNG is lossless. PNG->JPG is not. There is no way to prevent calibre from updating covers when ending books, short of disabling the EPUB metadata writer plugin.

04-11-2015, 05:07 AM	#6
GeoffR Wizard Posts: 3,821 Karma: 19162882 Join Date: Nov 2012 Location: Te Riu-a-Māui Device: Kobo Glo	Okay, so the workaround I have found is to edit metadata to remove the cover before sending the book to the device, and then add the cover back and upload the thumbnails with the KoboUtilities plugin. This results in JPG thumbnails but with the original PNG cover inside the book.

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