Photo taken on June 15, 2016 shows a Northern Song dynasty official Ru vase displayed in the Asian Art Museum of San Francisco, the United States. The Asian Art Museum of San Francisco put on a media preview of its exhibition "Emperors' Treasures: Chinese Art From Taipei Palace Museum" on Wednesday. The exhibition will present about 150 imperial artworks spanning the Song dynasty in the early 12th century to the Qing dynasty in the early 20th century between June 17 to September 18, 2016, with most of the pieces appearing for the first time in America. [Photo/Xinhua]