[gdal-dev] Idea: support JP2 TLM as sidecar in GDAL/OpenJPEG

[Even Rouault]

Hi,

Someone should just tell the team at ESA (are you reading us ESA by the 
way?) in charge of producing those JPEG2000 files to turn on the Kakadu 
switch to generate TLM markers. A 5 minute change on their side, ok 
maybe 1 hour to update unit tests.

What you suggest about sidecar .tlm sidecar could certainly be 
implemented, but one would have to rescan the archive to generate them. 
At that point, you'd probably just want to insert the TLM marker inside 
existing files with a dedicated utility that wouldn't need to decompress 
the pixel values.

See also https://mastodon.social/@EvenRouault/113556023446290151 for an 
alternate idea (not necessarily better).

Even


Le 13/12/2024 à 16:50, Jérémy Anger via gdal-dev a écrit :
> Dear GDAL maintainers,
>
> Thank you for the release of OpenJPEG 2.5.3, with the support of TLM 
> markers!
> Following up on [1], Sentinel-2 JP2 files currently do not have TLM 
> markers. However, it is theoretically possible to generate an external 
> index file for each JP2 raster, and the index could be formatted 
> exactly as a JP2 TLM marker. Such sidecar file is not part of the 
> JPEG2000 standard, but given the gains that are achievable with TLM 
> markers, this strategy sounds reasonable. The entirety of the 
> Sentinel-2 collection (archive and live) is concerned.
>
> GDAL could be modified to look for these sidecar .tlm files (although 
> I'm not too familiar with the sidecar system), and give the TLM marker 
> content to JP2 implementations (OpenJPEG in particular, after changes).
>
> Do you think this approach is reasonable? Would it be reasonable to 
> implement such a feature in GDAL and OpenJPEG?
> Do you have ideas for a better solution?
>
> Best regards,
> Jérémy
>
> [1]: https://lists.osgeo.org/pipermail/gdal-dev/2024-November/059805.html
>
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