Hi Even, I was thinking about your request to decode only a sub-window inside of a tile.
I don't think this is possible. Because of the serial nature the j2k decoding, there is no performance gain to only looking at a sub-window - the whole tile must be decoded. The only small gain is in memory : the final decoded region could fit in a smaller memory buffer. But, the speed will be the same for a tile or a sub-window. Cheers, Aaron On Sun, Dec 20, 2015 at 5:00 AM, Even Rouault <even.roua...@spatialys.com> wrote: > 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 > > -- > Spatialys - Geospatial professional services > http://www.spatialys.com >
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