[vtkusers] vtkImageActor can't display for certain SetDisplayExtent

[kdsfinger at gmail.com]

hi, all
I am following the example of Medical3. I read a stack image
(256x256x127, unsigned char png) from itk and passed to vtk. I checked
the vtkImageData, the values (size and pixel values) are all correct.
And here is the problem: it can only display with the
SetDisplayExtent(0,255, 0,255, z,z) (z set to 90~126 and everything
looks correct). It will display a pure blank white window if z sets
less than 90. Attached is the piece of my code mainly copyed from
Medical3.cxx. Thanks for comments.
zl2k

vtkImageMapToColors *axialColors = vtkImageMapToColors::New();
    axialColors->SetInput(data);//vtkImageData
    axialColors->SetLookupTable(hueLut);
    axialColors->Update();
  vtkImageActor *axial = vtkImageActor::New();
    axial->SetInput(axialColors->GetOutput());
    int p = (int)atoi(argv[1]);
    axial->SetDisplayExtent(0,255, 0,255, p,p);