HTJ2K

references

• https://jpeg.org/jpeg2000/htj2k.html
• https://github.com/chafey/HTJ2KResources
• https://htj2k.com/

HTJ2K is in a unique position to better address the goals of the responsive images initiative. Taking advantage of resolution scalability and random access capabilities, all desired resolution and cropping combinations of a single image can be efficiently served from a single JPH file, reducing the web server’s workload, and avoiding the proliferation of redundant representations

JPH comparison with JPG

JPH embeds an HTJ2K code-stream and JPG embeds a JPEG code-stream. The main aspects considered in this comparison

• are coding efficiency,
• encoding throughput
• decoding throughput

But it should be noted that HTJ2K offers a much larger set of extremely useful features than JPEG, including:

• HTJ2K/JPH offers multi-resolution access for free, while this is expensive and inefficient if included as an option with JPEG – progressive JPEG.
• HTJ2K/JPH offers region-of-interest accessibility, whereas JPEG files provide only a single monolithic representation of the source.
• HTJ2K/JPH offers non-iterative (one-pass) rate control, where a target compressed size can be achieved without iterative encoding, while JPEG does not offer this at all.
• HTJ2K/JPH offers very high precision, supporting virtually any type of HDR representation of interest, while JPEG is almost always limited to 8-bit precision – the 12-bit option is rarely used and slower.
• JPH offers a modern set of colour space descriptions, including HDR spaces.
• HTJ2K/JPH offers extremely high throughput lossless coding if required.
• Both HTJ2K/JPH and JPEG are intended to be royalty free standards.

conclusions

With similar or higher throughput to a heavily optimized implementation of the original JPEG algorithm (even single threaded), HTJ2K provides higher coding efficiency, resolution scalability, region-of-interest accessibility and much more parallelism. Image quality can be controlled using a recently established Qfactor, if desired, which substantially mimics the properties of the JPEG Qfactor, extending them to a much wider range of sample precisions and colour spaces. However, precise non- iterative rate control is also available (a well-known strength of JPEG 2000) and can even be combined with the Qfactor approach, to address a wide range of application needs, all while maintaining extremely high throughput. HTJ2K preserves almost all of the rich feature set of JPEG 2000, with the exception of quality scalability, offering an order of magnitude increase in throughput (i.e., vastly lower computational complexity) with approximately 5-10% reducing in coding efficiency. Moreover, the HT and original J2K-1 representations are fully interchangeable, allowing reversible transcoding to be incorporated at any point within a capture, distribution, archiving, caching or rendering system, to obtain the best features of both algorithms without sacrificing the integrity of the data. HTJ2K can even preserve all quality layering, profiles and other aspects of a non-HTJ2K code-stream during transcoding.