code: def pixel(self, ix, iy):
          
          x = (ix - self.xoffset + 0.5) / self.scale
          y = (iy - self.yoffset + 0.5) / self.scale
          z = complex(x, y)
          self.set_c(z)
          return self.mpixel(z)
docs: Return color for a pixel.
  
          Does translation from image coordinates (ix,iy) into
          the complex plane coordinate z = x+yi, and then calls
          self.mpixel(z) to find the color at point z.