Clara HD Does Kobo support CB7 files?

AudreyMedia · 09-16-2023, 03:34 PM

The official website tells me it supports CBZ and CBR files for comics and CB7 is the same idea but with 7zip compression. 7zip is slightly better compression so I wanted to make one. Anyone ever tried CB7 on a kobo?

NiLuJe · 09-16-2023, 04:02 PM

I would wager not. I would also wager this is a pointless endeavor, as you're archiving already compressed data (i.e., images). In fact, doing that sort of thing might lead to (very slightly) *larger* file sizes.

A sensible recommendation is in fact to use a zip container with *no* compression (i.e., store), for runtime performance reasons.

DNSB · 09-16-2023, 06:13 PM

In my limited testing, Kobo does not support CB7. OTOH, a 120MB CBZ file gave me a 122MB CBR file and and 118MB CB7 file so any savings are limited (I did not use the maximum compression algorithms for compatibility reasons).

AudreyMedia · 09-17-2023, 12:05 PM

Quote:

Originally Posted by DNSB

In my limited testing, Kobo does not support CB7. OTOH, a 120MB CBZ file gave me a 122MB CBR file and and 118MB CB7 file so any savings are limited (I did not use the maximum compression algorithms for compatibility reasons).

Thanks! I guess I'll just use CBZ

Anak · 09-17-2023, 03:08 PM

You can use 7zip to recompress existing .zip, .cbr, .cbz files to make them a little smaller (9- Ultra; zip). 7zip is usually a little better at compressing files than WinZip or WinRAR.

AudreyMedia · 09-17-2023, 09:00 PM

Quote:

Originally Posted by Anak

You can use 7zip to recompress existing .zip, .cbr, .cbz files to make them a little smaller (9- Ultra; zip). 7zip is usually a little better at compressing files than WinZip or WinRAR.

Thank you for the info I will do this henceforth

DNSB · 09-18-2023, 12:01 PM

For what it is worth, I just tested one of my daughter's manga files which gave me 202MB of image files.

7Zip 7z with Ultra and other settings for maximum compression gave me a 195MB output file.

7Zip Zip with Ultra and other settings for maximum compression gave me a 198MB output file.

WinRAR with maximum compression settings gave me a 197MB output file.

7Zip Zip with store (no compression) gave me a 202MB output file.

So compressing the already compressed image files does not yield great space savings. I lifted the settings for maximum compression from a couple of web sites. I'm not certain due to the dictionary size, that the zip and rar flavours would even work on a Kobo.

Quoth · 09-18-2023, 03:00 PM

Quote:

Originally Posted by DNSB

So compressing the already compressed image files does not yield great space savings. I lifted the settings for maximum compression from a couple of web sites. I'm not certain due to the dictionary size, that the zip and rar flavours would even work on a Kobo.

Seems like worthless savings for the effort.
Also how is image quality affected at any sharp boundaries?

Aleron Ives · 09-18-2023, 04:01 PM

Quote:

Originally Posted by Quoth

Also how is image quality affected at any sharp boundaries?

The compression is lossless, so image quality is not affected at all.

Quoth · 09-18-2023, 06:08 PM

Quote:

Originally Posted by Aleron Ives

The compression is lossless, so image quality is not affected at all.

I'm stupid. Of course it is lossless as it's designed for binary files.

The jpeg and other lossy formats are the ones that give big savings. It's pretty much a waste of effort compressing any compressed image format. Though jpeg works better on natural images than on comic graphics.

09-16-2023, 03:34 PM	#1
AudreyMedia Junior Member Posts: 3 Karma: 10 Join Date: Sep 2023 Device: Kobo Clara HD	Does Kobo support CB7 files? The official website tells me it supports CBZ and CBR files for comics and CB7 is the same idea but with 7zip compression. 7zip is slightly better compression so I wanted to make one. Anyone ever tried CB7 on a kobo?

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09-16-2023, 04:02 PM	#2
NiLuJe BLAM! Posts: 13,216 Karma: 25767288 Join Date: Jun 2010 Location: Paris, France Device: Kindle 2i, 3g, 4, 5w, PW, PW2, PW5; Kobo H2O, Forma, Elipsa, Sage, C2E	I would wager not. I would also wager this is a pointless endeavor, as you're archiving already compressed data (i.e., images). In fact, doing that sort of thing might lead to (very slightly) larger file sizes. A sensible recommendation is in fact to use a zip container with no compression (i.e., store), for runtime performance reasons.

09-16-2023, 06:13 PM	#3
DNSB Bibliophagist Posts: 29,425 Karma: 132241491 Join Date: Jul 2010 Location: Vancouver Device: Kobo Sage, Forma, Clara HD, Lenovo M8 FHD, Paperwhite 4, Tolino epos	In my limited testing, Kobo does not support CB7. OTOH, a 120MB CBZ file gave me a 122MB CBR file and and 118MB CB7 file so any savings are limited (I did not use the maximum compression algorithms for compatibility reasons).

09-17-2023, 03:08 PM	#5
Anak Fanatic Posts: 596 Karma: 641742 Join Date: Mar 2012 Location: DE Device: Kobo Glo	You can use 7zip to recompress existing .zip, .cbr, .cbz files to make them a little smaller (9- Ultra; zip). 7zip is usually a little better at compressing files than WinZip or WinRAR.

09-18-2023, 12:01 PM	#7
DNSB Bibliophagist Posts: 29,425 Karma: 132241491 Join Date: Jul 2010 Location: Vancouver Device: Kobo Sage, Forma, Clara HD, Lenovo M8 FHD, Paperwhite 4, Tolino epos	For what it is worth, I just tested one of my daughter's manga files which gave me 202MB of image files. 7Zip 7z with Ultra and other settings for maximum compression gave me a 195MB output file. 7Zip Zip with Ultra and other settings for maximum compression gave me a 198MB output file. WinRAR with maximum compression settings gave me a 197MB output file. 7Zip Zip with store (no compression) gave me a 202MB output file. So compressing the already compressed image files does not yield great space savings. I lifted the settings for maximum compression from a couple of web sites. I'm not certain due to the dictionary size, that the zip and rar flavours would even work on a Kobo.