Chaotic sequences have several good properties

such as the ease of their generation

their sensitive dependence on its initial parameters

and specially white noise alike

at the same time it can be reproduced precisely based on the initial condition

and their discrete mapping sequences have a same property.Because of these good properties

chaotic system can be used to image encryption and image preprocessing. In this paper

image encryption arithmetic is proposed based on chaotic system. First

based on the key (initial parameter is the key

here)

the chaotic sequences can be generated based on key

then it is mapped to the discrete 2 K value sequences

according to the discrete sequence

gray value of pixel is modified randomly

it is obvious that if attacker dose not know the key

the encrypted image will be looked like white noise and can not be rebuilt. There are many image encryption methods

and different arithmetic gets different results

but up to now there is no suit way to evaluate the result of image encryption. Based on image local variance and human vision system

an efficient definition of encryption degree is proposed. Preliminary results are satisfactory

and security of image completely depend on the key

slight error key results a different result. Hence

it can be used to encrypt image data.