[Gdal-dev] MrSID Driver v. 4.0.x overviews

[Julien Demaria]

Hi,

I' ve added overviews support in the new driver using MrSID DSDK v. 4.0.x 
and tested it (with OpenEV) under Windows with MrSID and JPEG2000 files ; 
and made minors modifications to update to the last DSDK 
"Geo_DSDK-4.0.9.713". (I've attached the zipped new mrsid\mrsiddataset.cpp 
file)

I've noted one bug with the driver when reading the last MrSID strip I 
believe (black zone under OpenEV) ; maybe a problem in the IReadBlock 
function on last truncated strip...
I suspect also another bug with nBlockSize that isn't well initialized when 
sample size > 8 bits
(Should I put a bug report in bugzilla ?)

About performances (tested with OpenEV) on a large RGB image (10000x10000), 
now large zoom-out are fast with overviews, but I find navigating in the 
image between 1/3 and 1/1 zoom factor is slow, and the viewer freeze for a 
moment before starting display tiles (initialization cost ?).
I cannot compare with old 3.x.x DSDK because I haven't one.

Maybe one reason is that to read an RGB image I believe each tile is 
decompressed 3 time, one time per component...
About the same problem with the GeoTIFF driver, Frank said that we can 
optimize this by reading interleaved data in one pass by using
the GDALDataset::RasterIO() ; maybe we can also implement this for the 
MrSID Driver ?
Maybe we can also try to remove the memcpy in the IReadBlock function and 
read directly data into the GDAL buffer.
(Maybe there are some optimization to do using the MrSID API differently ?)

I've a little question about JPEG2000 in MrSID : I see in 
Geo_DSDK-4.0.9.713/doc/README-3rdparty.txt that :
"This application uses Kakadu software, licensed from Unisearch Software, Ltd."
Is MrSID SDK use Kakadu for all its JPEG2000 support ?


Thanks in advance,

Julien 
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