@Ronounours. you, your team and collaborators are geniuses! Thank you very much!
Finally I have abandoned my old and beloved Kubuntu 14.04 to install Kubuntu 18.04. No available package has worked for qt version, but I have been able to compile qt version by myself.
Regarding these instructions:
http://gmic.eu/gimp.shtmlI guess these are for Xenial. Currently at 18.04 the packages "libcv-dev" and "libhighgui-dev" do not exist. I suppose that in 18.04 simply installs "libopencv-dev" and maybe "libopencv-highgui-dev".