def _is_displayable(structure):
    """ Determines if a PDS4 structure is displayable as an image.

    Displayable structures are PDS4 arrays are those that are either:
        (1) a 2D array, or
        (2) sub-types of Array_2D or Array_3D, or
        (3) have a display dictionary

    Parameters
    ----------
    structure : Structure
        PDS4 structure to check.

    Returns
    -------
    bool
        True if *structure* can be displayed as an image, False otherwise.
    """
    if structure.is_array():
        has_display_dict = structure.meta_data.display_settings is not None
        is_2d_array = structure.meta_data.num_axes() == 2
        if ('Array_2D_' in structure.type or 'Array_3D_' in structure.type or
            is_2d_array or has_display_dict):
            return True
    return False
