code: def ssim(a: np.array, b: np.array, **kwargs) -> float:
      """
      Calculate Structural Similarity Index Measure of two images (or explanations).
  
      Parameters
      ----------
      a: np.ndarray
           The first array to use for similarity scoring.
      b: np.ndarray
           The second array to use for similarity scoring.
      kwargs: optional
          Keyword arguments.
  
      Returns
      -------
      float
          The similarity score.
      """
      max_point, min_point = np.max(np.concatenate([a, b])), np.min(
          np.concatenate([a, b])
      )
      data_range = float(np.abs(max_point - min_point))
      return skimage.metrics.structural_similarity(
          im1=a,
          im2=b,
          win_size=kwargs.get("win_size", None),
          data_range=data_range,
      )
  
file_path: Quantus/quantus/functions/similarity_func.py
imports: from typing import Union
  import numpy
  import scipy
  import skimage
label_desc: Use image node_id 11 for calling a global function with example usage: ssim(a, b) and returns: skimage