[Insight-developers] readers and regions

[Damion Shelton]

Hi,

Wilson and I figured out (apparently) why the Difference of Gaussians 
gradient filter was breaking, in the context of our multiprocessor machine. 
The problem arises in the following lines:

<reader creation, initialization>
TImageType::Pointer inputImage = reader->GetOutput();
reader->Update();
inputImage->SetRequestedRegionToLargestPossibleRegion();

Later on the code, there is a mismatch between buffered, allocated, and 
requested regions, which causes pixel access to behave quite strangely. 
This problem goes away when we remove:

inputImage->SetRequestedRegionToLargestPossibleRegion();

Why does this work? What's bad about setting the requested region after an 
image is loaded?

Thanks,
-Damion-