def METHOD_NAME(data_format):
    """Set the value of the image data format convention.
    Args:
        data_format: string. `'channels_first'` or `'channels_last'`.
    Examples:
    >>> keras_core.config.image_data_format()
    'channels_last'
    >>> keras_core.config.set_image_data_format('channels_first')
    >>> keras_core.config.image_data_format()
    'channels_first'
    >>> # Set it back to `'channels_last'`
    >>> keras_core.config.set_image_data_format('channels_last')
    """
    global _IMAGE_DATA_FORMAT
    data_format = str(data_format).lower()
    if data_format not in {"channels_first", "channels_last"}:
        raise ValueError(
            "The `data_format` argument must be one of "
            "{'channels_first', 'channels_last'}. "
            f"Received: data_format={data_format}"
        )
    _IMAGE_DATA_FORMAT = data_format