[NTG-context] PNG pictures in original size

[Maurí­cio]

   Hi,

   When using bitmap figures (.png etc.) using \externalfigure, is it 
possible to set that I want the picture to have it's original size in 
pixels; or, better, that I don't want it to be scaled? I'm using some 
pictures that look terrible when converted to a different size, even if 
the new size is close to the original one.

   Thanks,
   Maurício