[vtkusers] how to get the data of the output of filters in a pipeline

[c v]

Hi, everyone,
I built a pipeline for image precessing in VC++.
I want to check the result of each filter and show
them .
But the codes as: this->pGaussSmoother->GetOutput()
returns NULL. 
 Why and how to get the output data?

Thanks in advance.

colin


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