Hi David,
I am so grateful for your assistance with this zero-filled background issue as well as the opacity issue (Cannot Control Opacity of vtkImageActors) discussed in another thread.
Using the stencil which can optionally be generated by vtkImageReslice was an absolute break-through for me. Finally, the reformatted image overlay makes sense. With your vtkStack, I was able to control the opacity, and with the stencil I was able to remove all of the background zeros.
I am also grateful for all of the help you provide to other vtk users. There is a lot of information in those posts. I have learned so much from you!
Best wishes,
Michelle