PSP ISO Compressor is, well, an ISO compressor for the PSP. Incredibly often, the need to shrink an ISO arises for the regular PC users, who have plenty of space at hand. It is no shock to hear that PSP users, who are limited to memory cards for ISO mounting on their units, need to compress ISO files.
Somebody thought of that problem and worked out a solution. That solution came in the form of a command-line application. Many users get terrified when faced to one of those, so another person created this front-end. A front-end is an application that provides a graphical user interface for a command-line application. PSP ISO Compressor, by danny_kay1710, works like a charm. You are provided with the ISO formats on the left. You have to select the format that you want to convert and to what format you would like to have it. After that, you can input your ISO file to the panel on the right and, at the bottom, there is the quality setting. There you have to select one of the many compression presets that there are.