Image dilation in Python as two separate 1-D passes

dilate-two-pass.py

def dilate_two_pass(x, window_size):
  m,n = x.shape
  k,l = window_size 
  y = np.empty_like(x)
  for i in xrange(m):
    for j in xrange(n):
      left_idx = max(0, i-k/2)
      right_idx = min(m, i+k/2+1) 
      currmax = x[left_idx, j]
      for ii in xrange(left_idx+1, right_idx):
        elt = x[ii, j]
        if elt > currmax:
          currmax = elt 
      y[i, j] = currmax 
  z = np.empty_like(x)
  for i in xrange(m):
    for j in xrange(n):
      left_idx = max(0, j-l/2)
      right_idx = min(n, j+l/2+1)
      currmax = y[i,left_idx]  
      for jj in xrange(left_idx+1, right_idx):
        elt = y[i,jj]
        if elt > currmax:
            currmax = elt
      z[i,j] = currmax
  return z