def __init__(self, tensor_name, prefix=None, map_func=None, scale=255):
        """
        Args:
            tensor_name (str): the name of the tensor.
            prefix (str): the filename prefix for saved images. Defaults to the Op name.
            map_func: map the value of the tensor to an image or list of
                 images of shape [h, w] or [h, w, c]. If None, will use identity.
            scale (float): a multiplier on pixel values, applied after map_func.
        """
        op_name, self.tensor_name = get_op_tensor_name(tensor_name)
        self.func = map_func
        if prefix is None:
            self.prefix = op_name
        else:
            self.prefix = prefix
        self.log_dir = logger.get_logger_dir()
        self.scale = scale

        Args:
            tensor_name (str): the name of the tensor.
            prefix (str): the filename prefix for saved images. Defaults to the Op name.
            map_func: map the value of the tensor to an image or list of
                 images of shape [h, w] or [h, w, c]. If None, will use identity.
            scale (float): a multiplier on pixel values, applied after map_func.
        
tensorpack/callbacks/graph.py