[gdal-dev] OpenJPEG

[Even Rouault]

Aaron,

> I am working on some performance enhancements for OpenJPEG,
> and I am curious about people's experience using the OpenJPEG driver with
> GDAL:
> 
> Does it have all the features you need, if not what is missing?

Being the developer of the driver, I believe it must be close to using the 
available capabilities of OpenJPEG as best as possible. I may have overlooked 
some features, so other eyes checking the code are always welcome.

From my point of view what is mainly missing in OpenJPEG (the lib):
- ability to decode efficiently sub-windows inside a tile (I guess this means 
using precincts). This is particuarly true for single-tiled big files
- reduce memory consumption. I've found that to decode a 2048x2048 tile of a 
Sentinel2 product, it takes 600 MB of memory whereas the uncompressed size of 
the tile is 8 MB (2048x2048*sizeof(int16)).
- ability to open files who have more than 2 gigapixels (or 4, I'm not sure 
where the limit is)
- currently the driver closes and reopen the file each time it reads a tile, 
because there are(were?) some instabilities in seeking through arbitrary tiles 
(ie reading potentially not in ascending tile order). Would be nice to be able 
to avoid that

> 
> Given that it is the slowest J2K library around, what would be acceptable
> performance in the geo-spatial world?

As fast as possible :-)

> These changes apply to the current master version of OpenJPEG, which will
> be released shortly.

Were you refering to this PR : https://github.com/uclouvain/openjpeg/pull/668 
?

Even

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