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I have folders of images that I would like to archive into back up drives and using winrar or a similar tool I would like to compress the files. They are (mostly - 99%) jpeg files.

In one archive I have 54 files at 114MB, when I use win rar, best compression method and check the "create solid archive" and the "lock archive" boxes I get a final size of 104MB, which is a compression of about 9%.

Is there a way to get even better compression using Winrar or another tool with tweaking setting etc to get a smaller archive?

Or is it the case that that is about the maximum compression I expect from such a task?

Note: I do not want to lose any more quality in the already compressed JPEG images so lossy compression is out of the question.

Aasim Azam
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3 Answers3

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You are unlikely to get any more compression than the little you got from WinRar. The reason is the fact you are trying to compress JPEG images. JPEG images are already compressed - it is built into the format. Read this Wikipedia article on JPEG, to learn more. In addition to that, JPEG compression is a lossy format. Images that you want to keep in the highest quality should not be saved in the JPEG format.

Keltari
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Try using a different archive format like .7z. It has been shown to produce marginally better compressed files compared to to other formats.

While using 7z to compress your documents, you can try the following settings to ensure the maximum compression for your documents.

While you did mention that you would not like to lose any quality in the image, the files you are storing (JPEG), are already lossy and compressed.

enter image description here

JPEG file sizes increases exponential with quality. Hence, you may be able to save some space by dropping your image quality slightly, such that no visible artifacts are produced, using a photo editing program and still save a respectable amount of space.

Community
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Carrein
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  • by lossy compression what I meant was - not to compress the images any more than they already are. – Aasim Azam Oct 04 '16 at 10:39
  • Have you tried a different archival format like 7z? Check out my post. Without any further modification of the images themselves, the only option left is to choose a more efficient archival format. – Carrein Oct 04 '16 at 11:19
  • It is noteworthy that zipx, introduced by Winzip in 2008 (!), is able to losslessly compress jpegs in an archive. So for pure archival purposes, it is not required to destruct image quality further. In my testing I got a 20% compression on pure screenshot jpegs, so for such an use case this would be worth considering.

    When it comes to lossy jpeg conversion, using the open source ImageMagick would be then a good choice.

     – Testerhood Feb 12 '23 at 13:45
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I convert my JPEGs to the newer JPEG XL format with lossless compression for a 20% reduction or more. The original photos (100% identical byte for byte) can be restored if needed. You can also go with "visually lossless" mode and get ~60% without noticing any difference in quality.

The downside is not many programs support JPEG XL directly (although you have a few options on Linux). The best option for all platforms is to convert with ImageMagick as part of your backup/restore process.

kontextify
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