High-throughput JPEG2000 (HTJ2K), also known as JPEG 2000 Part 15, is the most recent addition to the JPEG2000 suite of coding tools. The file extension JPH has been designated for compressed images employing this new part of the standard. This new part describes a “fast” block coder for the JPEG 2000 format, while retaining most other JPEG2000 features and capabilities intact. The HTJ2K block coder is amenable to parallelizable high-speed encoding and decoding implementations; moreover, it is designed to allow lossless transcoding of already compressed JPEG2000 images that employ the regular block coder. HTJ2K supports the scalability options available in the JPEG2000 format except for quality scalability, which is available only to a limited extent. This work gives a high-level overview of this new block coder; we also present preliminary performance results for a GPU implementation. We show that a low-end GPU can decode 4K 4:4:4 12-bit videos at more than 60 frames per second (fps) while a high-end GPU can decode 8K HDR videos at more than 120 fps.