Pop star Katy Perry belts out "I Kissed a Girl" in concert, in a scene from the documentary "Katy Perry: Part of Me." Courtesy Paramount Pictures Pop star Katy Perry (foreground) and her dancers perform her hit "Firework" in concert, in a scene from the documentary "Katy Perry: Part of Me." Courtesy Paramount Pictures Pop star Katy Perry, right, visits her grandmother, Ann Hudson, in Las Vegas, in a scene from the documentary "Katy Perry: Part of Me." Courtesy Paramount Pictures Pop star Katy Perry visits young fans backstage, in a scene from the documentary "Katy Perry: Part of Me." Courtesy Paramount Pictures