code: def isnr(vref, vdeg, vrst):
      
  
      msedeg = mse(vref, vdeg)
      mserst = mse(vref, vrst)
      with np.errstate(divide='ignore'):
          rt = msedeg / mserst
      return 10.0 * np.log10(rt)
docs: Compute Improvement Signal to Noise Ratio (ISNR) for reference,
      degraded, and restored images.
  
      Parameters
      ----------
      vref : array_like
        Reference image
      vdeg : array_like
        Degraded image
      vrst : array_like
        Restored image
  
      Returns
      -------
      x : float
        ISNR of `vrst` with respect to `vref` and `vdeg`