But this is quite a different format than JPEG or better said the subset of JPEG that we know today as JPEG format and the JPEG encoder/decoders support. The whole JPEG format did have support for a lossless mode for JPEG (different one than JPEG LS), arithmetic coding and 12-bit images too, but those features just didn't make it into the implementations of the format (arithmetic coding initially did, but was removed from popular implementations because of patents).