The role of を in this phrase 夜景を背景に歌舞伎の映像が流れます


I am reading this article
<http://www3.nhk.or.jp/news/html/20161005/k10010718561000.html> and come
across this phrase:

> 夜景を背景に歌舞伎の映像が流れます

I can get the general meaning but I'm not clear on what is the role of を in
the sentence.

