code: def backward(self,pixx,pixy):
          
          skyx,skyy = self.output.wcs_pix2world(pixx,pixy,self.origin)
          result = self.input.all_world2pix(skyx,skyy,self.origin)
          return result
docs: Transform pixx,pixy positions from the output frame back onto their
              original positions in the input frame.