There are two images of size M X N shown below.
In fact, my purpose was to create a topomap for the EEG signal, but it was difficult to use a known tool (e.g. EEGLAB), so I made it myself.
How do I make the black part in the right picture transparent and then overwrite the left picture? Or I would like to know how to show them at the same time.
The purpose is to make the following through two images.