  In this work we introduce a new notion called opacity complexity to measure
the complexity of automatic sequences. We study basic properties of this
notion, and exhibit an algorithm to compute it. As applications, we compute the
opacity complexity of some well-known automatic sequences, including in
particular constant sequences, purely periodic sequences, the Thue-Morse
sequence, the period-doubling sequence, the Golay-Shapiro(-Rudin) sequence, the
paperfolding sequence, the Baum-Sweet sequence, the Tower of Hanoi sequence,
and so on.
