Is there any official .cso compressor?

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Isn't this info good enough for you
http://sourceforge.net/projects/ciso/

Quote:Ciso is a small tool to compress your psp iso to cso format. It was originaly coded by Booster, the famous coder of Devhook for the PSP. Since Booster isn't maintaining his sources anymore, you can find them below.

My tool act as a gui for the dos program csio and the gui is sending command lines to csio only when csio finish doing what is doing to the image.

It also(ciso)saves the compressed image where you want and don't do anything to your ISO image.

You can never be 100% sure that everything will go ok no matter what software you use even if it's created by the most famous software developer in the world.

Most(if not all)programs created for personal use that modify data,almost always contains this message..."use it at your own risk"