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Old 10-11-2013, 05:12 AM   #1
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PNG Images in ePUB Files not rendered on Kobo

I have created my book in Sigil which uses many black and white images (line art style - scans of simple etched or vinyl cut prints). The PNG images display fine in Sigil and Calibre but are blank (white space) when downloaded to my Kobo Touch.

The KT is supposed to support PNG files, so I was wondering why it cannot render the images. The book has a few JPGs and they show fine in the KT.

The PNG files were created in Corel Paint Shop Pro X2 using a greyscale pallet and saved as PNG Non-Interlaced with Optimised Pallet.

I would like to keep the images in PNG format as a typical 17KB PNG image becomes a nasty 132KB when saved as JPG. I could reduce the JPG quality but I have to use a 90% compression factor to get the same size file while the image looks muddy and awful. As most images are a large white expanse with crisp black lines, I want to preserve this as much as possible.

Has anyone experienced this or could anyone suggest a solution? I don't know if it is limited to the Kobo.

Many Thanks.
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Old 10-11-2013, 06:57 AM   #2
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Originally Posted by DragonflyKing View Post
Has anyone experienced this or could anyone suggest a solution? I don't know if it is limited to the Kobo.
If you can share the EPUB, that would be fantastic. If not, can you please just upload the PNGs (or plop them in a sample EPUB and attach them to the post).

Can't know unless you post the images... I wouldn't mind tossing it on my Nook and seeing how these specific PNGs react... and also doing much closer analysis of the PNGs themselves.

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Has anyone experienced this or could anyone suggest a solution? I don't know if it is limited to the Kobo.
I recently stumbled upon some problems with certain Grayscale + Alpha PNGs here:

http://www.mobileread.com/forums/sho...d.php?t=223254

And also helping figure out some problems with 2-bit and 4-bit PNGs (which yours could potentially be):

http://www.mobileread.com/forums/sho...d.php?t=222916

As a side note: I have a sample PNG Test EPUB in both topics. Stick that on your Kobo and let me know how/if the Kobo displays all the PNGs.

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Originally Posted by DragonflyKing View Post
I would like to keep the images in PNG format as a typical 17KB PNG image becomes a nasty 132KB when saved as JPG. I could reduce the JPG quality but I have to use a 90% compression factor to get the same size file while the image looks muddy and awful. As most images are a large white expanse with crisp black lines, I want to preserve this as much as possible.
I like the way you think friend (I too am a huge proponent of PNG)!

Last edited by Tex2002ans; 10-11-2013 at 07:01 AM.
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Old 10-11-2013, 07:24 AM   #3
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Thanks Tex for your quick response. I've uploaded a small sample of the book here:
http://home.exetel.com.au/michaelrob...20Brigade.epub
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Old 10-11-2013, 06:08 PM   #4
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All images displayed fine on my Nook.

Is your Kobo having problems with specific images? Or are all the PNGs showing as blank white spaces?

I added 3 more versions (GIMP Grayscale, GIMP Indexed, and an optimized PNG) of your buzz image, let me know if those display on your Kobo at all.
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Old 10-11-2013, 09:18 PM   #5
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Wow, Thanks Tex but none of those buzz images displayed either.
All jpeg images display fine. Only the PNG files display as blank and it is all PNG files.
My Kobo Touch is running the latest firmware 2.6.1.

I've never noticed before but the feedbooks logo (a colour 32bpp PNG file) is not displaying in any of the books that I have downloaded from there. Maybe this issue is a Kobo thing?
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Old 10-11-2013, 09:33 PM   #6
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Aha! It looks like it is a known issue with the 2.6.1 Kobo firmware that I am running.
http://www.mobileread.com/forums/sho....php?p=2537441

Cool - I don't have to edit my entire book.
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Old 10-12-2013, 12:48 AM   #7
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Originally Posted by DragonflyKing View Post
Aha! It looks like it is a known issue with the 2.6.1 Kobo firmware that I am running.
http://www.mobileread.com/forums/sho....php?p=2537441

Cool - I don't have to edit my entire book.
Yes, this is a Kobo firmware issue.
The PNG will display fine if you force the reader to use the epub3
rendering engine.

The easiest way to do this is to obtain the Kobo Extended plugin
for Calibre which modifies the epub to look like the Kobo .kepub
format, which is rendered using the epub3 engine.

More info on the Kobo forum.
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Old 10-12-2013, 01:31 AM   #8
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Thanks DE, I went looking on the forum but found this thread saying that 2.6.2 no longer processes Calibre created epubs.
http://www.mobileread.com/forums/sho...d.php?t=224230

The add-on would be fine if it was just my person use I was concerned about but I am about to release my book to the public domain and don't expect anyone to have to tweak their software just to be able to read it.

It looks like 2.8.1 has been released; but as I am in Australia we are usually the last to receive it. I'll guess that I'll wait to see if that fixes the issue.
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Old 10-12-2013, 10:38 AM   #9
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Originally Posted by DragonflyKing View Post
Thanks DE, I went looking on the forum but found this thread saying that 2.6.2 no longer processes Calibre created epubs.
http://www.mobileread.com/forums/sho...d.php?t=224230

The add-on would be fine if it was just my person use I was concerned about but I am about to release my book to the public domain and don't expect anyone to have to tweak their software just to be able to read it.

It looks like 2.8.1 has been released; but as I am in Australia we are usually the last to receive it. I'll guess that I'll wait to see if that fixes the issue.
The thread title is a bit misleading.

I have 2.6.2 and Calibre is doing fine sending kepubs
to the reader. Apparently some minor stats features
are missing, but I hadn't noticed.

PNGs work fine.
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Old 10-12-2013, 10:48 AM   #10
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Yep; I just had a chance to try some tests and 2.6.2 worked fine with sideloaded kEpubs on a Mini.
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Old 10-12-2013, 11:00 AM   #11
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Also I just tried this book on a newer, beta build of the Kobo f/w on a Glo and all images were viewable.
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Old 10-12-2013, 01:44 PM   #12
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Also tried the book on my Mini with 2.6.2, as a straight ePub, copied directly
to the reader (no Calibre) - i.e. using the epub2 rendering engine and it all works fine.
So I guess the png bug is fixed in 2.6.2.
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Old 10-12-2013, 08:28 PM   #13
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Wow, thanks a lot guys for taking the time to download the book and checkout the issue. Your feedback is very helpful.

Cheers.
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