This never worked before. Better be happy that the swivel mode is working at all :D!

There is a small chance for a quick fix: I know that you can set a certain "background color" for the vtkReslicer. If we set that to transparent, the issue could perhaps be solved, however, there is a high chance that this will interfere somehow with 2D rendering of multiple images.

@Tobi S.: Are you participating in bsq. right now? Could you have a look at this or instruct someone how to do it? Should be rather simple to test.

I'm currently not able to participate on bugsquashing. But the background colour quickfix should be easy. I'll find someone for next bsq.

Have the constants changed with the changes Markus made to clipping stuff, LevelWindowFilter etc.?

There's a setter for background color in VtkImageReslice - VtkImageReslice::SetBackgroundLevel. We are using a fixed value set to -32768 in case of a PlaneGeometry (line 203) and in case of an abstract geometry e.g. ThinPlateSplineCurvedGeometry we set the background color to -1023 (line 251). The code snippets were taken from ImageVtkMapper2D and the documentation says that -32768 is translucent and -1023 black. We should check these values and provide a setter for ExtractSliceFilter to change values in runtime.

Current release is finished. Resetting target milestone