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Compression Understanding


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#1 arphot

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Posted 20 March 2010 - 09:27 AM

I am at a bit of a loss due to my lack of understanding the archiving process using programs such as WinZip & 7-Zip. I always thought that these programs could reduce the size of files considerably, but that's not the results that I have been getting. Mostly, a 50 Meg (a combination of several JPEGs) file only loses about 2 or 3 Megs. Are these programs supposed to compress more? My particular scenario is that I am trying to get these compressed archives to no more than 30 Megs for uploading to a website forum. I'd like to include several JPEGs in a compressed file, but only get four successfully (in order to get near the limit for upload) as they are high resolution images (post processed as well) and weigh a bit more than usual. Any help in the understanding of this process would be greatly appreciated. Thanks again for being the best group on the web for resolving computerly issues. Kirk

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#2 Animal

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Posted 20 March 2010 - 11:43 AM

Since you are not getting much compression which for Hi Res graphics is a good thing. I'm assuming you are using a lossless compression application.

Take a look here to understand why you aren't getting what you think you should and how file compression works: How File Compression Works. by Tom Harris.

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#3 arphot

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Posted 20 March 2010 - 11:57 AM

Thanks Animal. I was always under the impression that the archiving process only stores the compressed files & that they return to their original size(s) when opened from the archive. I also read somewhere (right after posting this) that since JPEGs are compressed already that compressing them wouldn't be practical and size difference would be barely noticeable. I'm just going to have to make smaller ZIPs with less files in them. Thanks again! Kirk




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