Hi Simon,
thank you for beeing insistent! I recognized that the changes that I made to get the "open(...)" macro run, were causing problems when n-dimensional images have been processed. Originally, when n-dimensional images (e.g. X,Y,C) are used as input, you can select "X,Y" and the macro will be applied plane-wise for each plane (i.e. iterating over the non-selected dimensions). That didn't work anymore.
But I resolved it and it should work now with the next nightly build as desired again (i.e. than your workflow works without selecting the C-dimensions and an (X,Y,C=4)-image will result in an (X,Y,C=4) image where each X,Y-plane (4 planes) are background-corrected).
Sorry for beeing inattentive and thanks for your help.
Best,
Martin