import vtk
from vtk.util.misc import vtkGetDataRoot
VTK_DATA_ROOT = vtkGetDataRoot()

reader = vtk.vtkPNGReader ()
reader.SetDataSpacing (0.8, 0.8, 1.5)
reader.SetFileName ( VTK_DATA_ROOT + "/Data/fullhead15.png")

iren = vtk.vtkRenderWindowInteractor()

viewer = vtk.vtkImageViewer2()
viewer.SetInput ( reader.GetOutput() )
viewer.SetupInteractor (iren)

viewer.GetRenderer().SetPixelAspect( 1, 1.5)
#viewer.GetRenderer().ComputeAspect()

iren.Initialize()
iren.Start()