[gdal-dev] Proper parameters for GDALBeginAsyncReader() for RGB images

[Frank Warmerdam]

On Thu, Jun 17, 2010 at 11:03 AM, Zermeno, Robert J CIV NAVAIR,
472100D <robert.zermeno at navy.mil> wrote:
>
> GDALBeginAsyncReader(fileDataset,
>        0, 0,                           //Start at top-left position
>        ImageWidth, ImageHeight,        //Note, I am requesting whole image.
>        JPIP_Buffer,
>        BufferXSize,
>        BufferYSize,
>        GDT_Byte,
>        colorScheme,
>        Bandmap,
>        0,
>        0,
>        0,
>        0);
>
>
> Under the hood, how does the function take the original image size and scale it down to fit
> Into the a size much smaller than original? For some reason, when I do this for RGB color
> Images, it gives a AccessViolation error when it calls GDALARGetNextUpdatedRegion().  However,
> For Grayscale images, it works fine.  What would you think might be the problem?

Robert,

Your call parameters seem fine.  I do not understand
why you are having problems.  If you are unable to get it
to work, feel free to file a ticket with a small compilable
code example demonstrating the problem, and setup to
access a public server or data source.

You asked "how does the function take the original
image and scale it down to fit in a much smaller image".
I'm not sure if you are looking for internal details or just
whether you are requesting this properly from the outside.
If you need details about the internals I can try to provide.

Best regards,
-- 
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