…I’m ashamed to admit it, yes. I double checked and this is the cause. Thanks.
Still, with this test case working in Ubuntu, while not working in Manjaro, while working OK in java code that uses imread, I conclude something in my java code for generation of the wiener filter or the filter2dfreq is the cause. (I have only just switched to manjaro from ubuntu - mid December - but this “black image” problem existed on ubuntu before that).
I’m going to back to basics and strip out all my javafx code and other stuff so that I have a bare java reproduction of the out_of_focus sample.
Thanks again.