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Old 11-10-2019, 09:40 PM   #1
20191110
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Solution for opening large .cbz files

I bought my Libra H2O a few months ago. One of the things I was looking forward to the most was reading my backlog of comic books purchased through Humble Bundle. Much to my disappointment, most of the .cbz files I attempted to open would trigger an error saying that the file was corrupted.

I found the solution to this problem a few days ago, and came here to share! It turns out that .cbz files are nothing more than a .zip file containing an image for every page. Page arrangement works based on the alphabetic sort order of each image's file name. To get a large .cbz file to open, you need to reduce the file size of the embedded pages. In every case I've tried, simply resizing pages to fit within the Libra's screen without scaling is enough. I set them to gray-scale at the same time. The end result is that I am finally able to open these files. Even .cbz files that opened previously are able to turn pages faster.
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Old 11-10-2019, 11:25 PM   #2
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1. How large?
2. How did you "simply resizing pages to fit within the Libra's screen without scaling is enough. I set them to gray-scale at the same time. "?
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Old 11-11-2019, 01:24 AM   #3
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Originally Posted by codychan View Post
1. How large?
I am not able to open .cbz files that are larger than about 200MB.

Quote:
2. How did you "simply resizing pages to fit within the Libra's screen without scaling is enough. I set them to gray-scale at the same time. "?
I extract the .cbz file into a folder, use ImageMagick's command-line "convert" tool to resize all of them in bulk, and zip them back up again. The following example produces nice-looking results that fit each page within the Libra's screen without any stretching:

Code:
convert source.jpg -resize 1264x1680 -colorspace gray -quality 80 destination.jpg
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Old 11-12-2019, 01:22 PM   #4
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Quote:
Originally Posted by 20191110 View Post
I bought my Libra H2O a few months ago. One of the things I was looking forward to the most was reading my backlog of comic books purchased through Humble Bundle. Much to my disappointment, most of the .cbz files I attempted to open would trigger an error saying that the file was corrupted.
If you have one, I would suggest just reading CBZ files on a tablet. Android has lots of good free comic apps: Perfect Viewer and Challenger Comics are good and ad-free.

On Windows, selection is more limited. I use Cover on my Surface. Comics look terrific on it.

I love my e-ink readers for novels. But not comics.
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Old 11-12-2019, 04:34 PM   #5
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You can do what the OP suggested and be fine, but if you don't want to install Imagemagick or aren't comfortable with command line utilities, you could also use Kindle Comic Converter instead. Select your device and it'll automatically choose the resolution of your device and scale the image down if it's larger, or upscale the image if it's smaller if you choose. You can also do multiple items in a batch, convert between cbz, cbr and image pdfs, and there are options to convert all color images to grayscale to save space, and to automatically trim margins to maximize the amount of image displayed on the screen (although test the option first; if there's a small image in the corner used as a chapter or issue divider surrounded by nothing but whitespace, it'll crop all of the whitespace out leaving you with a giant version of that image which may not be what you want).

My favorite part of it though is that it saves you from having to manually unzip/rezip files. That right there is a time saver!

And if those image files are DRM free, you could also try installing koreader onto the device and using that to view them. It uses MuPDF as its image renderer for comic files, and while it can't handle cbr (since the rar format isn't technically open source), it is faster than the Adobe renderer used by Kobo, and it might be able to handle those large files with no modification. The latest versions now support the Libra too.

Last edited by rtiangha; 11-12-2019 at 04:43 PM.
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Old 11-14-2019, 02:06 AM   #6
20191110
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Quote:
Originally Posted by ZodWallop View Post
If you have one, I would suggest just reading CBZ files on a tablet. Android has lots of good free comic apps: Perfect Viewer and Challenger Comics are good and ad-free.

On Windows, selection is more limited. I use Cover on my Surface. Comics look terrific on it.

I love my e-ink readers for novels. But not comics.
I can use Atril on my computer, and maybe I'll give one of those Android apps a try for any colorized comic books. For comics that are already in black and white, I've been surprised how nice they look an eink.
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Old 11-14-2019, 02:15 AM   #7
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Quote:
Originally Posted by rtiangha View Post
You can do what the OP suggested and be fine, but if you don't want to install Imagemagick or aren't comfortable with command line utilities, you could also use Kindle Comic Converter instead.
Thanks for those tips. I wasn't aware of any automatic conversion tools. I'll probably stick with my current method. It's working for me and I like being able to make small tweaks to the conversion for each comic.

One think I've noticed is that the .cbz files look better when they have been optimized for the device they are read on. Even on my computer screen, scaling the pages to fit my monitor yields better results than letting my reader software scale them as they are read.
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