• Current Optics and Photonics
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• v.3 no.4
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• pp.320-328
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• 2019

A method for joint-transform correlator (JTC) multiple-image encryption based on a quick-response (QR) code key is proposed. The QR codes converted from different texts are used as key masks to encrypt and decrypt multiple images. Not only can Chinese text and English text be used as key text, but also symbols can be used. With this method, users have no need to transmit the whole key mask; they only need to transmit the text that is used to generate the key. The correlation coefficient is introduced to evaluate the decryption performance of our proposed cryptosystem, and we explore the sensitivity of the key mask and the capability for multiple-image encryption. Robustness analysis is also conducted in this paper. Computer simulations and experimental results verify the correctness of this method.

• Journal of the Korean Society of Safety
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• v.14 no.2
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• pp.192-199
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• 1999

We propose a rotation invariant fingerprint identification system based on the circular harmonic filter(CHF) and binary phase extraction joint transform correlator(BPEJTC) for validation and security verification. It is shown that this system has the shift and rotation robust properties and can recognize the fingerprint in real-time. The complex circular harmonic filter, which is used to obtain the rotation invariance, is converted into the real-valued filter for real-time implementation. Experimental results show that this system has a good performance in the rotated fingerprints.

• Journal of Astronomy and Space Sciences
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• v.26 no.4
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• pp.567-588
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• 2009

Korea-Japan Joint VLBI Correlator (KJJVC) is being developed by collaborating KASI (Korea Astronomy and Space Science Institute), Korea, and NAOJ(National Observatory of Japan), Japan. In early 2010, KJJVC will work in normal operation. In this study, we developed the software correlator which is based on VCS (VLBI Correlation Subsystem) hardware specification as the core component of KJJVC. The main specification of software correlator is 8 Gbps, 8192 output channels, and 262,144-points FFT (Fast Fourier Transform) function same as VCS. And the functional algorithm which is same as specification of VCS and arithmetic register are adopted in this software correlator. To verify the performance of developed software correlator, the correlation experiments were carried out using the spectral line and continuum sources which were observed by VERA (VLBI Exploration of Radio Astrometry), NAOJ. And the experimental results were compared to the output of Mitaka FX correlator by referring spectrum shape, phase rate, and fringe detection and so on. Through the experimental results, we confirmed that the correlation results of software correlator are the same as Mitaka FX correlator and verified the effectiveness of it. In future, we expect that the developed software correlator will be the possible software correlator of KVN (Korean VLBI Network) with KJJVC by introducing the correlation post-processing and modifying the user interface as like GUI (Graphic User Interface).

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.3
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• pp.19-32
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• 2003

In the conventional photorefractive joint transform correlator(PRJTC), the intensity ration of input signal-to-pump beam should be large enough to saturate two-beam coupling transfer function to obtain a desired correlation result. As a result, the signal-to-noise ratio(SNR) of correlation result is decreased in a noisy input image. In this paper, we propose the improved method for increasing the SNR of the PRJTC by using the characteristics of BaTiO$_3$. We stop the energy transfer saturating by low intensity ratio of input beam and realize a short length of effective interaction in BaTiO$_3$ by making large incident angle of the signal beam. So the gain in high frequency area is decreased and the gain in low frequency area comes up to the saturation gain of the beam coupling transfer function. Therefore the SNR is improved in noisy input image and the PRJTC can be easily realized by low intensity ratio of input beam.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.6
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• pp.178-188
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• 1996

In this paper, we propose a new opto-digital object recognition system which has rotation, scale, and shift invariant characteristics. The fourier power spectrum of the object image is modified to get shift invariance. The log-polar transform is used for rotation and scale invariance. And the decision of similarities is performed by nonlinear joint transform correlator (NJTC) that can control the ratio of phase and amplitude signals. Experimental verification of th eproposed optical object recognition system is presented.

• Proceedings of the IEEK Conference
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• 2002.07a
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• pp.450-453
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• 2002

In this paper a Phase-based virtual image encryption and decryption techniques based on a joint transform correlator (JTC) are proposed. In this method, an encrypted image is obtained by multiplying a phase-encoded virtual image that contains no information from the decrypted image with a random phase. Even if this encryption process converts a virtual image into a white-noise-like image, the unauthorized users can permit a counterfeiting of the encrypted image by analyzing the random phase mask using some phase-contrast technique. However, they cannot reconstruct the required image because the virtual image protects the original image from counterfeiting and unauthorized access. The proposed encryption technique does not suffer from strong auto-correlation terms appearing in the output plane. In addition, the reconstructed data can be directly transmitted to a digital system for real-time processing. Based on computer simulations, the proposed encryption technique and decoding system were demonstrated as adequate for optical security applications.

• Korean Journal of Optics and Photonics
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• v.1 no.2
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• pp.130-134
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• 1990

In this paper, pSDF-based referance image is reahzed. Using BJTC(binary joint transform correlator) as nonlinear correlator, optical pattern recognition for interclass discrimination is performed. Experimental results show that correlation peak intensity of one calss is two times higher than that of the other class, which indicates its superiority in discrimination sensitivity.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.10
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• pp.152-159
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• 1996

We have designed and implemented an optoelectronic hardware of binary phase extraction joint transform correlator (BPEJTC) which provides higher peak-to-sidelobe ratio than many other versions of JTC that has been published so far and does not produce correlation peaks due to intra-class association, to construct a multi-target tracking system. The digital processing unit controlling the entire system plays the part of modifying and binarizing the joint transform power spectrum (JTPS) and the optical processing unit is mainly used to take fourier transform operations. Some experimental results conducted by designed system along with its architecture showed the processing rate of 6 frames per second, thereby the potential applicability of the proposed system to real-time multitarget tracking system is given.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.11
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• pp.111-118
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• 1990

In this paper, pSDF-based referance image is realized. Using BJTC (binary joint transform correlator) as the spatial plane correlator, optical pattern recognition for interclass identification and interclass discrimination is performed. Computer simulation shows that the correlation performance of BJTC is superior to that of JTC. Experimental results using BJTC reveal that correlation peak intensity is constant within the error rang from $4.1{\%}\to\9.6{\%}$ in interclass identification and correlation peak intensity of one class is two times higher than that of the other class in interclass discrimination, which indicates its superiority in discrimination sensitivity.

• Korean Journal of Optics and Photonics
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• v.14 no.3
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• pp.255-259
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• 2003

In this paper, we propose an improved image encryption and decryption method using a virtual image and a joint transform correlator (JTC). The encrypted image is obtained by the Fourier transform of the product of a virtual-phase image and a random-phase image, and a Fourier transform of the decrypting key generated by the proposed phase assignment rule is used as the Fourier decrypting key. Based on the solution, the original image is reconstructed using JTC in the frequency-domain. The proposed method using a virtual image, which does not contain any information from the original image, prevents the possibility of counterfeiting by unauthorized people. And also the auto-correlation terms, which are the drawback of a JTC system, contribute to reconstructing the original image rather than to disturbing its identification. But because phase-only encryptions are sensitive to noise and scratches, phase errors can be generated in fabricating the encrypted image or the Fourier decrypting key so the errors that are responsible for degradation of the quality of the reconstructed image are analyzed and the solution is demonstrated. Computer simulations show the solution, and the proposed method is very useful for JTC architecture.