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TOPIC: Optimal 7z/CB7 compression settings...

Optimal 7z/CB7 compression settings... 9 years 3 months ago #1739

  • vixenfinder
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Hey All,
I want to start up a discussion to get the best settings for compressing comics into 7z format and get some feedback on ideas.

After about a good few days of testing, I've found that 7z for me worked best as:
Compression: Normal
Compression Method: LZMA
Dictionary Size: 6MB (Need Some Input on what the "Dicionary" exacly is)
Word size:128 (Didn't really see any performance loss)
Solid Block Size: 8MB

I believe that cYo stated that it was specifically the Solid Block size that was causing the massive delays because of the large amount of decompression that goes into the files as a whole. From my testing I've decided that 8MB gave me delays no longer than 2 seconds on random seeks. I look forward to your thoughts.


P.S. Also I've found that compressing from BMP format gave better compression results than jpg.
Last Edit: 9 years 3 months ago by vixenfinder.
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Re:Optimal 7z/CB7 compression settings... 9 years 3 months ago #1740

  • AlucardNoir
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a) jpeg are already compressed using rar so it won't do anything or barely anything for you, on the other hand tif, png, bmp, these formats need compression and it really is observable.

b) the size of the solid archive isn't the problem, the solid archive is the problem, read about it on the internet, just google it, the idea behind it is that it theoretically takes less space once compressed but it also means that the entire archive is treated as a mono block which means one error can cause a ton of trouble [especially since 7zip doesn't support any restore properties - so one error can kill your comic or most of what is after the error]

Edit: the idea is that being mono block the entire archive needs to be scanned for every picture and this causes the delay in CR or any other picture viewer that can look into archives
MangAnime Vampire AlucardNoir
Last Edit: 9 years 3 months ago by AlucardNoir.
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Re:Optimal 7z/CB7 compression settings... 9 years 3 months ago #1743

  • Quaraxkad
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vixenfinder wrote:
Dictionary Size: 6MB (Need Some Input on what the "Dicionary"
exacly is)

The dictionary is basically the reason that compression works. The software looks within each file to find matching blocks of data, adds it to the dictionary, removes it from the file, and adds a reference in the file to the dictionary. A common analogy is to look at an actual sentence or paragraph that contains the same word multiple times. Instead of repeating that word over and over again, it goes in the dictionary just one time. The word size is the maximum length in bytes of each dictionary "entry".

vixenfinder wrote:
Dictionary Size: 6MB (Need Some Input on what the
I believe that cYo stated that it was specifically the Solid Block size that was causing the massive delays because of the large amount of decompression that goes into the files as a whole.

As AlucardNoir said, it's not the size of the solid block, it's the fact that there is one to begin with. In a normal archive, each file is compressed seperately, each with their own dictionary. In a solid archive, each file is treated as one and use the same dictionary. It's very usefull when you have a large number of similar files that aren't compressible on their own, but since they are so similar, sharing a dictionary will greatly reduce the size.
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Re:Optimal 7z/CB7 compression settings... 9 years 3 months ago #1744

  • Zengei
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For my own conversion I use compression: fastest and turn off solid blocks. Space saving is minimal per comic using compression instead of store (no compression) but it added up to about a savings of ~500MB over my entire collection when converting from CBZ to CB7.
http://www.zengei.com/images/offsite/comicsig/random.php
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Re:Optimal 7z/CB7 compression settings... 9 years 2 months ago #1841

I have tested 7z with several of the settings.

First I tried all settings from Store to Ultra compression level, and with solid archives (I know, I know) turned on and off.

Solid 7z archives were somewhat smaller than orginal cbr files above "normal", however unsolid ones were always too big even in Ultra setting. :(

Finally I found that if compression method Deflate is choosen instead of the default LZMA, the efficiency of compression is much better in case of comic books, usually beats original cbr files a bit.

Here are my final settings (word size can be changed between 8-255 but I found no difference):

Compression level: Normal
Compression method: Deflate
Dictionary size: 32k
Word size 32

Try it! B)
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