Some ripping applications dump a UMD as files instead of a ISO image, an example is UMD Tool. You can convert the files into an ISO, CSO, DAX or EZIP image using either UMDGen or Epsilon’s EZIP Tool. UMDGen supports conversion to ISO, CSO and DAX. The Epsilon EZIP tool allows conversion from ISO to EZIP, but you cannot reverse the process.
Please remember that ripping games is illegal unless you own the game.