A Review of Some Recent Work in the Area of Imaging and Optical Signal Processing <s> Optical Encryption <s> A novel technique for multiplexing complex images is proposed in which each image may be demultiplexed only if a set of random encryption keys is known. The technique utilizes the ability of the double random phase encoding method to spread a signals’ energy in both the space and the spatial frequency domains in a controlled manner. To multiplex, images are independently encrypted with different phase keys and then superimposed by recording sequentially on the same material. Each image is extracted by using the particular key associated with it. During decryption the energy from the other images is further spread, making it possible to minimize its effects by using suitable filters. Wigner analysis is applied to the technique, and numerical results are presented. © 2007 Optical Society of America OCIS codes: 070.6020, 090.4220, 070.2580. <s> BIB001 </s> A Review of Some Recent Work in the Area of Imaging and Optical Signal Processing <s> Optical Encryption <s> We perform a numerical analysis of the double random phase encryption-decryption technique to determine how, in the case of both amplitude and phase encoding, the two decryption keys (the image- and Fourier-plane keys) affect the output gray-scale image when they are in error. We perform perfect encryption and imperfect decryption. We introduce errors into the decrypting keys that correspond to the use of random distributions of incorrect pixel values. We quantify the effects that increasing amounts of error in the image-plane key, the Fourier-plane key, and both keys simultaneously have on the decrypted image. Quantization effects are also examined. <s> BIB002 </s> A Review of Some Recent Work in the Area of Imaging and Optical Signal Processing <s> Optical Encryption <s> We discuss a projection system for real world three-dimensional objects using spatial light modulators (SLM). An algorithm to encode the digital holograms of real world objects on to an SLM is presented. We present results from experiments to project holograms of real world holograms using a nematic liquid crystal SLM. We discuss the case when the pixel sizes of the charge-coupled device (CCD) and SLM used for recording the hologram and projection are different. <s> BIB003 </s> A Review of Some Recent Work in the Area of Imaging and Optical Signal Processing <s> Optical Encryption <s> A phase encoded image is encrypted using the double random phase encoding technique, (DRPE). The effects of using a variable dynamic range of phase distribution during phase encoding (pre-encryption) are examined. We begin by phase encoding the input image using the full phase range, fromp to p. We perform numerically perfect encryption and we then introduce errors into the decrypting phase-keys in the form of a pseudo-random distribution (position and phase) of incorrect pixels values. By quantify- ing the resulting error in the attempted decryptions, for increasing amounts of error in the decrypting phase-keys, we examine the effects of reducing the phase range to, +/� (pD). In this way we attempt to improve the phase encoding procedure for use with the DRPE technique. When the pixel values calcu- lated, during an attempted decryption, fall outside the phase range used to phase encode the assigned input image, we examine different methods of redistributing the value of that pixel to an assigned value within the allowed phase range. The effects of the phase quantisation used in the keys are also examined. <s> BIB004 </s> A Review of Some Recent Work in the Area of Imaging and Optical Signal Processing <s> Optical Encryption <s> An optical implementation of the amplitude encoded double random phase encryption/decryption technique is implemented, and both numerical and experimental results are presented. In particular, we examine the effect of quantization in the decryption process due to the discrete values and quantized levels, which a spatial light modulator SLM can physically display. To do this, we characterize a transmissive SLM using Jones matrices and then map a complex image to the physi- cally achievable levels of the SLM using the pseudorandom encoding technique. We present both numerical and experimental results that quantify the performance of the system. © 2009 Society of Photo-Optical Instru- <s> BIB005
There has been significant interest in encryption schemes which can be implemented optically BIB002 BIB003  BIB004 BIB005  . Practical optical implementation of such systems is difficult BIB003 BIB005 and the security and robustness of these systems is still a matter of study and analysis BIB002  BIB004 BIB005  . However not only do such systems pose a very interesting problem for the fast algorithms described above in Section 3, it has been shown that the problems of encryption and multiplexing can be discussed fruitfully using PSO BIB001 .