[NTG-context] locate figure (mkiv)

Hi, I have some general graphics, which I would like to access from the lua side. The graphics are added to the graphic search path via \setupexternalfigures[locations={local,global,default}, directory={<path to graphics>}] What I now need is a way in lua to locate the graphics (no inclusion) and to get the full path of the file. I have looked into 'the base' but couldn't find a way to do it. Peter