anchor.diff:  
       ! header
       write(99,111) "P3"
  -    write(99,222) width, height, 256
  +    write(99,222) width, height, 255
   
       ! pixel data
  -    do x = 1, width
  -      do y = 1, height
  -        write (99,333) image(:,x,y)
  -      end do
  -    end do
  +    write (99, *) image
  +    !do x = 1, width
  +    !  do y = 1, height
  +    !    write (99,333) image(y,x,:)
  +    !  end do
  +    !end do
   
       ! close ppm file
       close (99)
  
positive.code:     offset = cmplx(x_center - 0.5*pixel_size*width, &
      y_center + 0.5*pixel_size*height)
  
      do x = 1, width
        do y = 1, height
          coord = offset + cmplx(x*pixel_size, -y*pixel_size)
          image(:,x,y) = to_rgb(pixel_value(coord, 256))
        end do
      end do
  
    end function image
  
  
negative.code:     if ( present(n_max) ) then
        n_end = n_max
      else
        n_end = 255
      end if
      z1 = 0
  
      do n = n_end, 0, -1
        if (abs(z1) > r_max) then
          pixel_value = n
          !write (*, *) n
          return
        end if
        z1 = z1**2 + z
  