[NTG-context] Centering an image in framed.

I am using framed and externalfigure commands. I want to put a rule around the image; however, the image has space around all sides. It appears that the top, right, and left sides has the same gap. However, the bottom side has a huge (by comparison) gap. So I can't use a negative offset to fix the problem. How do I center the image & place a border? \framed[location=middle,height=fit,width=fit,rulethickness=1.0pt]{% \externalfigure[image-01.png][maxwidth=3cm,maxheight=4cm] } Thanks, Bart