Transcode DICOM to HTJ2K format

[Saveriu]

I see that dcm4che can now read htj2k format but it would be great to have the capability to transcode to that format (in dcm2dcm for example).

[gunterze]

dcm4che relies on J2K codecs provided by OpenJPEG/OpenCV, which currently only supports HTJ2K decoding/decompression, but not HTJ2K encoding/compression. uclouvain/openjpeg#1381

[gunterze]

@aous72 in uclouvain/openjpeg#1487 (comment)_ :

I think it is easiest for you guys if OpenJPEG had HTJ2K encoding support.

Let me describe the current status of HTJ2K in OpenJPH.
OpenJPH encodes quantized coefficient (for lossy) or transformed coefficients (lossless) using one cleanup pass that encodes all the bitplanes in these coefficients.
Rate-control is currently driven by the quantization step size; finer quantization step sizes produce larger files with better quality.

A proper rate-control, in which you specify the desired rate, is missing. To do this properly, I need two more passes, the significance propagation pass (SPP) and the magnitude refinement pass (MRP), together with error estimation, and some post-compression rate-distortion method. These are missing from OpenJPH.
Of course, an alternative is to use the Qfactor method, as described in an ISO document, which is also missing from OpenJPH.

It is easiest to add what exists in OpenJPH to OpenJPEG. It is also possible to hack some sub-optimal rate-control into the existing OpenJPEG rate control mechanism. It is sub-optimal because it lacks SPP and MRP.

I just need to find the time to do it. I would be happy if someone else did it.

Cheers,
Aous.

[jeremy-nocek-rp]

@gunterze I'm curious if you've heard any updates outside of the linked thread. In your post, you mentioned that you're considering integrating OpenJPH as a stop gap until OpenJPEG provides HT2JK encoding, but their response was left pretty open ended.