Sounds like it will just take an existing JPEG and reduce the size, but not re-compress it - so even though the original JPEG is lossy, there will be no additio

Sounds like it will just take an existing JPEG and reduce the size, but not re-compress it - so even though the original JPEG is lossy, there will be no additional loss introduced, whereas another format not based on JPEG would require a re-encode pass that would lose additional information.