外文翻譯---級聯(lián)迭代傅里葉變換算法在光學安全中的應用

1、英文文獻原文A cascaded iterative Fourier transform algorithmfor optical security applicationsAbstract:A cascaded iterative Fourier transform (CIFT) algorithm is presented for optical security applications. Two phase-masks are

2、 designed and located in the input and the Fourier domains of a 4-f correlator respectively, in order to implement the optical encryption or authenticity verification. Compared with previous methods, the proposed algori

3、thm employs an improved searching strategy: modifying the phase- distributions of both masks synchronously as well as enlarging the searching space. Computer simulations show that the algorithm results in much faster con

4、vergence and better image quality for the recovered image. Each of these masks is assigned to different person. Therefore, the decrypted image can be obtained only when all these masks are under authorization. This key-a

5、ssignment strategy may reduce the risk of being intruded.Key words: Optical security – optical encryption – cascaded iterative Fourier transform algorithm1. IntroductionOptical techniques have shown great potential

6、in the field of information security applications. Recently Réfrégier and Javidi proposed a novel double-random-phase encoding technique, which encodes a primary image into a stationary white noise. This techni

7、que was also used to encrypt information in the fractional Fourier domain and to store encrypted information holographically. Phase encoding techniques were also proposed for optical authenticity verification. Wang et

8、 al and Li et al proposed another method for optical encryption and authenticity verification. Unlike the techniques mentioned above, this method encrypts information completely into a phase mask, which is located in e

9、ither the input or the Fourier domain of a 4-f correlator. For instance, given the predefinitions of a significant image f(x, y) as the desired output and a phase-distribution exp{jb(u, v)} in the Fourier domain, it’s

10、 easy to optimize the other phase function exp{jp(x, y)} with a modified projection onto constraint sets (POCS) algorithm [10]. Therefore the image f(x, y) is encoded successfully into exp{jp(x, y)} with the aid of ex

11、p{jb(u, v)}. In other words, the fixed phase exp{jb(u, v)} serves as the lock while the retrieved phase exp{jp(x, y)} serves as the key of the security system. To reconstruct the original information, the phase functio

12、ns exp{jp(x, y)} and exp{jb(u, v)} must match and be located in the input and the Fourier plane respectively. Abookasis et al implemented this scheme with a joint transform correlator for optical verification. However

13、, because the key exp{jp(x, y)} contains information of the image f(x, y) and the lock exp{jb(u, v)}, and the 4-f correlator has a character of linearity, it is possible for the intruder to find out the phase-distribut

14、ion of the lock function by statistically initialization of the phase-distributions of the masks. Suppose the iteration process reaches the kth iteration (k = 1, 2, 3, …), and the phase-distributions in the input and the

15、 Fourier plane are represented as and , respectively. Then an estimation of the target image is obtained at the output of the correlator defined by where FT and IFT denote the Fourier transform and the inverse Fourier t

16、ransform, respectively.If fk(x,y)satisfies the convergent criterion, the iteration process stops, and and are the optimized distributions. Otherwise, the fk(x,y) is modified to satisfy the target image constraint as fol

17、lows Then the modified function is transformed backward to generate both of the phase-distributions as follows where ang{ · } denotes the phase extraction function. Then k is replaced by k+1 for the next iteration.

18、It is shown in Eqs. 3(a) and 3(b) that both of the phase-distributions are modified in every iteration, accorded to the estimation of the target image in the present iteration. It ensures he algorithm converges with much

19、 faster speed and more consistent for the phase-masks. In general, the convergent criterion can be the MSE or the correlation coefficient between the iterated and the target image, which are defined by where M*N is the