code: def _hog_channel_gradient(channel):
      """Compute unnormalized gradient image along `row` and `col` axes.
  
      Parameters
      ----------
      channel : (M, N) ndarray
          Grayscale image or one of image channel.
  
      Returns
      -------
      g_row, g_col : channel gradient along `row` and `col` axes correspondingly.
      """
      g_row = np.empty(channel.shape, dtype=channel.dtype)
      g_row[0, :] = 0
      g_row[-1, :] = 0
      g_row[1:-1, :] = channel[2:, :] - channel[:-2, :]
      g_col = np.empty(channel.shape, dtype=channel.dtype)
      g_col[:, 0] = 0
      g_col[:, -1] = 0
      g_col[:, 1:-1] = channel[:, 2:] - channel[:, :-2]
  
      return g_row, g_col
  
imports: import numpy
  from .None import _hoghistogram
  from .._shared import utils
label_desc: Use image node_id 2 for calling a global function with example usage: _hog_channel_gradient(channel) and returns: g_row,  g_col