1 May 2014 Generation of keys for image optical encryption in spatially incoherent light aimed at reduction of image decryption error
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At present time methods of optical encryption are actively developed. The majority of existing methods of optical encryption use not only light intensity distribution, easily registered with photosensors, but also its phase distribution which require application of complex holographic schemes in conjunction with spatially coherent light. This leads to complex optical schemes and low decryption quality. To eliminate these disadvantages it is possible to implement optical encryption using spatially incoherent illumination which requires registration of light intensity distribution only. However this applies new restrictions on encryption keys: Fourier spectrum amplitude distribution of encryption key should overlap Fourier spectrum amplitude distribution of image to be encrypted otherwise loss of information is unavoidable. Therefore it seems that best key should have white spectrum. On the other hand due to fact that only light intensity distribution is registered, spectra of image to be encrypted and encryption key always have peaks at zero frequency and their heights depend on corresponding total energy. Since encrypted image contains noise, ratio of its average spectrum energy to noise average energy determines signal to noise ratio of decrypted image. Therefore ratio of amplitude at zero frequency to average spectrum amplitude (RZA) of encryption key defines decrypted images quality. For generation of encryption keys with low RZA method of direct search with random trajectory (DSRT) was used. To estimate impact of key RZA on decrypted images error numerical experiments were conducted. For experiments keys with different RZA values but with same energy value were generated and used. Numerically simulated optical encryption and decryption of set of test images was conducted. Results of experiment demonstrate that application of keys with low RZA generated by DSRT method leads to up to 20% lower error in comparison to keys generated by means of uniform random distribution.
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Pavel A. Cheremkhin, Pavel A. Cheremkhin, Nikolay N. Evtikhiev, Nikolay N. Evtikhiev, Vitaly V. Krasnov, Vitaly V. Krasnov, Vladislav G. Rodin, Vladislav G. Rodin, Sergey N. Starikov, Sergey N. Starikov, "Generation of keys for image optical encryption in spatially incoherent light aimed at reduction of image decryption error", Proc. SPIE 9131, Optical Modelling and Design III, 913125 (1 May 2014); doi: 10.1117/12.2052723; https://doi.org/10.1117/12.2052723

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