Some types of files compress better than others. For example, most multimedia files already exist in a highly compressed state. The standards for these file types usually specify efficient techniques to compress the data they contain. Examples include, but are not limited to, graphic (picture) files (GIF, JPG, etc), music files (MP3, WMA, etc), and movie files (AVI, MPG, etc). Once a file has been compressed, it usually cannot be compressed more to any significant extent. Therefore, such files don't get much, if any, smaller when they are added to a Zip file (.zip or .zipx). For sending photos by email, you may want to consider resizing them.
You would see a similar lack of compression if you zipped some files using maximum compression and then added that Zip file to another Zip file. This second Zip file would not be substantially smaller than the first one (it may even be slightly larger). Again, this is because the data in the original Zip file is already compressed.
There are other file types that don't compress well. For example, certain types of encrypted data files, such as those used by home finance programs and some database products, will not compress very much.
By contrast, some data files (such as text files and picture files in the BMP format) can often be compressed by 90% or more; while some types (such as program files) are often compressed by 50% or so.
|If you are using WinZip 12 or later with JPG files, you can use Best method and compress your JPG files up to 20% more without loss of quality. With this setting, WinZip will use Jpeg compression with your JPG files and the result will be a Zipx file. If you are planning to share these Zip files with others, you should be sure that they are also using WinZip 12 or later.
Again, if you create Zip files and see files that cannot be significantly compressed, it is probably because they already contain compressed data or they are encrypted.
If you have any questions, please email Technical Support.
Varying File Compression Explored
Default compression - What it is, how to change it
Settings Tab - WinZip Ribbon
What is the difference between "Legacy" and "Best method" compression?
What is a Zipx File?
Using Jpeg compression in WinZip