Reverse the normalization done to a batch of images.

        Arguments:
            arr: of shape/size (N,3,sz,sz)

def denorm(self,arr):
        """Reverse the normalization done to a batch of images.

        Arguments:
            arr: of shape/size (N,3,sz,sz)
        """
        if type(arr) is not np.ndarray: arr = to_np(arr)
        if len(arr.shape)==3: arr = arr[None]
        return self.transform.denorm(np.rollaxis(arr,1,4))