In the world of PS3 emulation and homebrew, a standard ISO (or "JB Folder" format) contains the full data of a game disc. When you see files advertised as "highly compressed" (e.g., a 20GB game shrunk to 500MB), you should proceed with extreme caution for several reasons:
Result: A 45GB game becomes ~16GB. Load times improve by 20%. Visuals are identical. ps3 iso highly compressed extra quality
Here is what you need to know about PS3 compression and quality: The Reality of Compression In the world of PS3 emulation and homebrew,
Full ISO: The most stable format for CFW and Cobra-enabled PS3s. a 20GB game shrunk to 500MB)