NITF with JPEG2000

Describe the question.

I’m interested in using the python API to decode a NITF file containing a very large image encoded with JPEG2000. A NITF is a container format, encapsulating a header and one or more images. When using JPEG2000 compression, image data is effectively a .jp2 file encapsulated within a larger NITF file.

I’m currently able to discover the extents of the encapsulated image data through other means, read the complete (very large) encoded image to a python variable as bytes, form a code stream from those encoded bytes, and then decode a numpy array for the small ROI I’m interested in. Unfortunately this is relatively inefficient as I have to read and store the complete encoded image just to decode a small portion.

One useful possibility would be a new code stream constructor that takes a file name, byte offset, and byte length. This would let me form a code stream from just the relevant JP2 portion of the encapsulating NITF without reading all bytes into memory.

Would such a constructor be possible? Or is there some other way to achieve decoding for a container format like NITF without reading the entire byte stream to memory?

Thanks in advance for any help!

Check for duplicates

• I have searched the open bugs/issues and have found no duplicates for this bug report

Start with the Python API's current code-stream constructor and the path that decodes a NumPy ROI from encoded bytes. Investigate whether it can read a bounded byte range from an NITF container without loading the full JPEG2000 payload; done means a documented, working approach for decoding the small ROI with bounded input memory.