Function heif_image_add_component 

pub unsafe extern "C" fn heif_image_add_component(
    image: *mut heif_image,
    width: c_int,
    height: c_int,
    component_type: u16,
    datatype: heif_component_datatype,
    bit_depth: c_int,
    out_component_id: *mut u32,
) -> heif_error

— adding components to a heif_image (encoder path)