Image encryption with fractional wavelet packet method

We introduce a new method called fractional wavelet packet transform to encrypt images in this paper, in which fractional orders and wavelet packet filter are its two series of keys. Fractional orders are additional keys in this method compared to wavelet packet encryptions. Selected image encryption is also proposed in this paper, and it is quite more flexible and effective than wavelet, fractional wavelet or wavelet packet encryptions. The possible optical implementation and digital computation are proposed. Computer simulations prove its feasibility.