[gdal-dev] OpenJpegDataset IReadBlock question

[Joaquim Luis]

On 10-04-2012 13:14, Robert Zermeno wrote:
> Ladies and Gents,
>
> I have yet to properly configure GDAL to compile with a repository 
> OpenJpeg V2, but I wanted to see how GDAL uses openjpeg tile request.  
> I created my own project and modified IReadBlock() to be standalone to 
> view a tile request.
>

This is probably not of much help because I did nothing special to build 
GDAL with OpenJpeg V2 on Windows using VS2010. I compiled OpenJpeg with 
the help of the CMake scripts and than linked as explained on nmake.opt.
I did not do any particular testing, but for example running with this 
test file looks fine

C:\programs\GDALtrunk\gdalautotest-1.8.0\gdrivers\data>gdalinfo byte.jp2
Driver: JP2OpenJPEG/JPEG-2000 driver based on OpenJPEG library
Files: byte.jp2
Size is 100, 100
Coordinate System is:
PROJCS["NAD27 / UTM zone 11N",
...

Joaquim

>
> I am using a sample data file provided by openjpeg data folder named 
> p1_04.j2k.  How is the data retrieved from opj_decode_tile_data() is 
> being stored in the buffer?  To access pixel 0, is it just buffer[0] 
> or is there another way?
> For some reason, my request for Tile (0,0) of length 128x128 returns 
> an image that looks masked.  The image is mostly black and white with 
> no depth of shading (i.e. missing information).
> This image also uses 12 bits-per-pixel which I do not see where GDAL 
> truncates the image data down to 8 bits-per-pixel.  Does GDAL return 
> the raw 12 bits-per-pixel forcing the user to truncate the data 
> properly for every pixel or is it handled by GDAL (If so, where)?
>
> I hope to figure out why GDAL does not link properly to openjpeg V2 
> for others use this option again.  I hope someone can provide me the 
> answers to the questions I have asked.
>
> Thanks,
>
> John
>
>
>
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