Based on [vtkImageStack example](https://examples.vtk.org/site/Cxx/Images/ImageStack/), the rendering is wrong if I replace the `vtkImageSlice` class by `vtkImageActor`. Theses two classes looks to be equivalent. It's after this test that I noticed that `vtkImageActor` is deprecated. Good rendering (`vtkImageSlice`)  Bad rendering (`vtkImageActor`). No transparency (border of each image) and wrong color.  VTK : 9.3