[gdal-dev] GDAL and JPEG2000 (Kakadu specially), manually reading image data

Zermeno, Robert J CIV NAVAIR, 472100D robert.zermeno at navy.mil
Tue Apr 6 15:16:50 EDT 2010

Can anyone let me know how to properly read a 24bpp JPEG2000 image data?  This image has 1 Band overview.  I am using the C API.

I have a few questions.  Please respond even if you know something about any of the questions I have.

1.  Can someone reference me to where I can acquire what Band overviews are in respect to JPEG2000?

2. What does GDALGetOverview() really return when referring to image data?  I understand it returns a GDALRasterBandH in which I can call GDALReadBlock(), but it does not successfully (I believe its because my image array is not big enough).

3. In GDALReadBlock(), what does it mean when this method returns a "natural" block from the raster band?  So, since my image is say 24bpp 900 x 900, will return a line of 900 x 3 (for RGB per pixel)?

4.  When using GDALReadBlock() when the image has an overview, I still retrieve image data before even calling GDALGetOverview().  What data am I actually getting?

My main issue is understanding how the image data in JPEG2000 is retrieved by GDAL and what GDALGetOverview() and GDALReadBlock() really returns to the programmer when your image contains an Overview? 

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