code: def bbox(img):
      
      rows = np.any(img, axis=1)
      cols = np.any(img, axis=0)
      rmin, rmax = np.where(rows)[0][[0, -1]]
      cmin, cmax = np.where(cols)[0][[0, -1]]
  
      return rmin, rmax, cmin, cmax
docs: Find the bounding box around nonzero elements in the given array
  
      Copied from https://stackoverflow.com/a/31402351/5703449 .
  
      Returns:
          rowmin, rowmax, colmin, colmax