That's a different codec for a different application. "Unlike J2K-1, the HT coder is not fully embedded and hence quality scalability is largely sacrificed." [1

That's a different codec for a different application. "Unlike J2K-1, the HT coder is not fully embedded and hence quality scalability is largely sacrificed." [1] The outer file format with the metadata has some commonality, but that's about it. [1] https://ds.jpeg.org/whitepapers/jpeg-htj2k-whitepaper.pdf https://ds.jpeg.org/whitepapers/jpeg-htj2k-whitepaper.pdf