PNG images losing quality.

piau9000 · 02-02-2018, 12:09 PM

Hi. I'm facing some problems with image quality for quite some time and I can't find what may be causing it.

Somehow, when I add a epub file to calibre, it converts some images from PNG to JPG and then back to PNG. You can cleary see it as it generates all the usual garbage that JPG adds (around texts for example it looks like literal puke).

Also it seems to affect only cover images. The other ones are not touched.

What is causing it?
The PNG inside the original epub is perfect as I compared it pixel by pixel with the source. But the PNG inside the epub on the calibre folder is clearly JPG.
I'm not talking about the small JPG file on the same folder, as it is indeed a lower quality JPG. I'm talking about the one inside the epub file.

Is there a way to make it stop?

JSWolf · 02-02-2018, 12:43 PM

You want to set the output profile to tablet to stop images from being changed.

piau9000 · 02-02-2018, 02:23 PM

Quote:

Originally Posted by JSWolf

You want to set the output profile to tablet to stop images from being changed.

Did not work.
After futher testing it seems to only happen when you edit a book. It seems that, when it create a instance for you to edit the book, it converts the cover image to JPG.
So whenever you are saving it, you need to replace the cover image with the lossless original image, otherwise it will save the low quality version instead.

Really weird.

JSWolf · 02-02-2018, 02:55 PM

Try going into the editor and then...

edit > preferences > integration with calibre > uncheck update metadata embedded in the book when opening

Also, make sure you are running the latest version. I've never had the graphics auto-convert. It doesn't do that here.

kovidgoyal · 02-02-2018, 09:57 PM

When you open a file to edit, it's metadata, including cover is updated, if you dont want that to happen, turn off the option for it in the editor preferences under calibre integration.

piau9000 · 02-03-2018, 12:23 PM

Quote:

Originally Posted by JSWolf

Try going into the editor and then...

edit > preferences > integration with calibre > uncheck update metadata embedded in the book when opening

Also, make sure you are running the latest version. I've never had the graphics auto-convert. It doesn't do that here.

Quote:

Originally Posted by kovidgoyal

When you open a file to edit, it's metadata, including cover is updated, if you dont want that to happen, turn off the option for it in the editor preferences under calibre integration.

That did it.

Thanks.

It also resolved some other issues that I was having.

Terisa de morgan · 02-03-2018, 01:02 PM

Thank you, I didn't understand the duplicated images

02-02-2018, 12:09 PM	#1
piau9000 Junior Member Posts: 3 Karma: 10 Join Date: Feb 2018 Device: none	PNG images losing quality. Hi. I'm facing some problems with image quality for quite some time and I can't find what may be causing it. Somehow, when I add a epub file to calibre, it converts some images from PNG to JPG and then back to PNG. You can cleary see it as it generates all the usual garbage that JPG adds (around texts for example it looks like literal puke). Also it seems to affect only cover images. The other ones are not touched. What is causing it? The PNG inside the original epub is perfect as I compared it pixel by pixel with the source. But the PNG inside the epub on the calibre folder is clearly JPG. I'm not talking about the small JPG file on the same folder, as it is indeed a lower quality JPG. I'm talking about the one inside the epub file. Is there a way to make it stop?

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02-02-2018, 12:43 PM	#2
JSWolf Resident Curmudgeon Posts: 73,983 Karma: 128903378 Join Date: Nov 2006 Location: Roslindale, Massachusetts Device: Kobo Libra 2, Kobo Aura H2O, PRS-650, PRS-T1, nook STR, PW3	You want to set the output profile to tablet to stop images from being changed.

02-02-2018, 02:55 PM	#4
JSWolf Resident Curmudgeon Posts: 73,983 Karma: 128903378 Join Date: Nov 2006 Location: Roslindale, Massachusetts Device: Kobo Libra 2, Kobo Aura H2O, PRS-650, PRS-T1, nook STR, PW3	Try going into the editor and then... edit > preferences > integration with calibre > uncheck update metadata embedded in the book when opening Also, make sure you are running the latest version. I've never had the graphics auto-convert. It doesn't do that here.

02-02-2018, 09:57 PM	#5
kovidgoyal creator of calibre Posts: 43,859 Karma: 22666666 Join Date: Oct 2006 Location: Mumbai, India Device: Various	When you open a file to edit, it's metadata, including cover is updated, if you dont want that to happen, turn off the option for it in the editor preferences under calibre integration.

02-03-2018, 01:02 PM	#7
Terisa de morgan Grand Sorcerer Posts: 6,233 Karma: 11768331 Join Date: Jun 2009 Location: Madrid, Spain Device: Kobo Clara/Aura One/Forma,XiaoMI 5, iPad, Huawei MediaPad, YotaPhone 2	Thank you, I didn't understand the duplicated images

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