code: def roberts(image, mask=None):
      """Find the edge magnitude using Roberts' cross operator.
  
      Parameters
      ----------
      image : 2-D array
          Image to process.
      mask : 2-D array, optional
          An optional mask to limit the application to a certain area.
          Note that pixels surrounding masked regions are also masked to
          prevent masked regions from affecting the result.
  
      Returns
      -------
      output : 2-D array
          The Roberts' Cross edge map.
  
      See also
      --------
      roberts_pos_diag, roberts_neg_diag : diagonal edge detection.
      sobel, scharr, prewitt, skimage.feature.canny
  
      Examples
      --------
      >>> from skimage import data
      >>> camera = data.camera()
      >>> from skimage import filters
      >>> edges = filters.roberts(camera)
  
      """
      check_nD(image, 2)
      out = np.sqrt(
          roberts_pos_diag(image, mask) ** 2
          + roberts_neg_diag(image, mask) ** 2
      )
      out /= np.sqrt(2)
      return out
  
imports: import numpy
  from scipy import ndimage
  from scipy.ndimage import binary_erosion, convolve
  from .._shared.utils import _supported_float_type, check_nD
  from ..restoration.uft import laplacian
  from ..util.dtype import img_as_float
label_desc: Use image node_id 14 for calling a global function with example usage: roberts(image, mask) and returns: out