I have put together the best methods to compress and decompress isos to cso format and vice versa, This are the best compressors you can find online.
Open it and then just open the ISO/CSO you want to convert with it and click save -> ISO or CSO (see image below)
That’s it, if you get an error when opening UMDGEN, try the solution below:
To solve that you must disable DEP (Data Execution Prevention) for UMDGen: Right click My Computer (Computer), Properties, Click Advanced, Click Settings button in Performance section, Click Data Execution Prevention Tab. Select second radial button, and add UMDGen to the list. That should stop it from crashing as soon as it opens.
Extract it and open the program, to convert ISO to CSO use the compress tab to convert CSO to ISO use the decompress tab, click the folder icon to search for the ISO/CSO and click the disk icon to select where to save it. Finally Click GO! Button. (See image below)
This is a hidden gem of ISO compressors, it’s the only one that can handle files larger than 2 GBs, ideal for large isos such as Final Fantasy Type-0 merged ISO.