Works with Zero and Minimum background value options, only "custom" results in an uncaught "dimension (4) is not in (2)(3)" exception + crash.

Also, dynamic image + static segmentation disables the image masking widgets with the message "Different image sizes cannot be masked". Tested with 2d+t and 3d+t image.

I also looked into this task yesterday and the issue is that for custom background values, the "AccessByItk_n" function is used, which only works for 2D and 3D images. A potential fix would be to use the "AccessFixedDimensionByItk_n" function for the 4D case, then the Workbench does not crash anymore. So in the QmitkImageMaskingWidget.cpp one could replace

AccessByItk_n(referenceImage, GetRange, (bottom, top));

by

if (referenceImage->GetDimension() == 4)
{
  AccessFixedDimensionByItk_n(referenceImage, GetRange, 4, (bottom, top));
}
else
{
  AccessByItk_n(referenceImage, GetRange, (bottom, top));
}

However, I'm not sure if this is the best solution