code: def blend(self, other):
          
          raise NotImplementedError("This method has not be implemented for "
                                    "xarray support.")
  
          if self.mode != "RGBA" or other.mode != "RGBA":
              raise ValueError("Images must be in RGBA")
          src = other
          dst = self
          outa = src.channels[3] + dst.channels[3] * (1 - src.channels[3])
          for i in range(3):
              dst.channels[i] = (src.channels[i] * src.channels[3] +
                                 dst.channels[i] * dst.channels[3] *
                                 (1 - src.channels[3])) / outa
              dst.channels[i][outa == 0] = 0
          dst.channels[3] = outa
docs: Alpha blend *other* on top of the current image.