• Journal of Korea Multimedia Society
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• v.19 no.6
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• pp.1043-1051
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• 2016

In this paper, double encryption technique of binary image using random phase mask and 2-step phase-shifting digital holography is proposed. After phase modulating of binary image, firstly, random phase mask to be used as key image is generated through the XOR operation with the binary phase image. And the first encrypted image is encrypted again through the fresnel transform and 2-step phase-shifting digital holography. In the decryption, simple arithmetic operation and inverse Fresnel transform are used to get the first decryption image, and second decryption image is generated through XOR operation between first decryption image and key image. Finally, the original binary image is recovered through phase modulation.

• Proceedings of the IEEK Conference
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• 2002.07a
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• pp.631-634
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• 2002

In this paper, we propose an improved optical security system using three phase-encoded images and the principle of interference. This optical system based on a Mach-Zehnder interferometer consists of one phase-encoded virtual image to be encrypted and two phase-encoded images, encrypting image and decrypting image, where every pixel in the three images has a phase value of '0' and '$\pi$'. The proposed encryption is performed by the multiplication of an encrypting image and a phase-encoded virtual image which dose not contain any information from the decrypted image. Therefore, even if the unauthorized users steal and analyze the encrypted image, they cannot reconstruct the required image. This virtual image protects the original image from counterfeiting and unauthorized access.. The decryption of the original image is simply performed by interfering between a reference wave and a direct pixel-to-pixel mapping image of the encrypted image with a decrypting image. Both computer simulations and optical experiments confirmed the effectiveness of the proposed optical technique for optical security applications.

• Journal of the Optical Society of Korea
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• v.6 no.4
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• pp.156-160
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• 2002

In this paper, we propose an improved optical security system using three phase-encoded images and the principle of interference. This optical system based on a Mach-Zehnder interferometer consists of one phase-encoded virtual image to be encrypted and two phase-encoded images, en-crypting image and decrypting image, where every pixel in the three images has a phase value of '0'and'$\pi$'. The proposed encryption is performed by the multiplication of an encrypting image and a phase-encoded virtual image which dose not contain any information from the decrypted im-age. Therefore, even if the unauthorized users steal and analyze the encrypted image, they cannot reconstruct the required image. This virtual image protects the original image from counterfeiting and unauthorized access. The decryption of the original image is simply performed by interfering between a reference wave and a direct pixel-to-pixel mapping image of the en crypted image with a decrypting image. Computer simulations confirmed the effectiveness of the proposed optical technique for optical security applications.

• Journal of the Optical Society of Korea
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• v.19 no.3
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• pp.241-247
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• 2015

The double-random phase encryption (DRPE) algorithm is a robust technique for image encryption, due to its high speed and encoding a primary image to stationary white noise. Recently it was reported that DRPE in the Fresnel domain can achieve a better avalanche effect than that in Fourier domain, which means DRPE in the Fresnel domain is much safer, to some extent. Consequently, a method based on DRPE in the Fresnel domain would be a good choice. In this paper we present an image-authentication method which uses only partial phase information from a double-random-phase-encrypted image in the Fresnel domain. In this method, only part of the phase information of an image encrypted with DRPE in the Fresnel domain needs to be kept, while other information like amplitude values can be eliminated. Then, with the correct phase keys (we do not consider wavelength and distance as keys here) and a nonlinear correlation algorithm, the encrypted image can be authenticated. Experimental results demonstrate that the encrypted images can be successfully authenticated with this partial phase plus nonlinear correlation technique.

• 한국가시화정보학회:학술대회논문집
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• 2002.11a
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• pp.7-10
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• 2002

A novel two-phase PIV algorithm using a single camera has been proposed, which introduces a method of image-separation into respective phase images, and is applied to freely rising single bubble. Gas bubble, tracer particle and background each have different gray intensity ranges on the same image frame when reflection and dispersion in the phase interface are intrinsically eliminated by optical filters and fluorescent material. Further, the signals of the two phases do not interfere with each other. Gas phase velocities are obtained from the separated bubble image by applying the two-frame PTV. On the other hand, liquid phase velocities are obtained from the tracer particle image by applying the cross-correlation algorithm. Moreover, in order to increase the SNR (signal-to-noise ratio) of the cross-correlation of tracer particle image, image enhancement is employed.

• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.62-63
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• 2003

We propose an improved image encryption and the shift-tolerance method in the Fourier space using a virtual phase image. The encrypted image is obtained by the Fourier transform of the product of a phase-encoded virtual image, not an original image, and a random phase image. We demonstrate the robustness to noise, to data loss and shift of the encrypted image or the Fourier decryption key in the proposed technique.

• 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.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.9
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• pp.658-665
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• 2003

In this paper, we propose an improved image encryption and the shift-tolerance method in the Fourier space using a virtual phase image. The encrypted image is obtained by the Fourier transform of the product of a phase-encoded virtual image, not an original image, and a random phase image. Therefore, even if unauthorized users analyze the encrypted image, we can prevent the possibility of counterfeiting from unauthorized people using virtual image which dose not contain any information from the original image. The decryption technique is simply performed by inverse Fourier transform of the interference pattern between the encrypted image and the Fourier decrypting key, made of proposed phase assignment rule, in frequency domain. We demonstrate the robustness to noise, to data loss and shift of the encrypted image or the Fourier decryption key in the proposed technique.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 2001.05a
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• pp.64-76
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• 2001

In this paper, A simple image hologram encryption and decryption technique based on the principle of interference are proposed. The technique using the photorefractive material for getting a stable interference pattern is also proposed. And combine these two techniques, I would like to implement a stable optical information security system. In the encrypting process, I would generate binary phase hologram which can reconstruct original image perfectly, and regard this hologram as original image to be encrypted image. And then the hologram is encrypted as randomly generated binary phase image. Reference image is also generated from the encrypted image by applying interference rule. In the decrypting process, I can get a interference intensity by interfering the reference image and the encrypted image in the interferometer. and transform inferference intensity information into phase information. I recover original image by inverse Fourier transforming the phase information. In this process, the intensity information generated by interference of two images is very sensitive to external vibrations. So, I would like to get a stable interference using the characteristic of SPPCM(self pumped phase conjugate mirror) in photorefractive materials, especially BaTiO₃.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.6 s.336
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• pp.31-38
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• 2005

In this paper, we proposed an optical security system based on a gray-image exclusive-OR encryption using multi-phase separation and phase-wrapping method. For encryption, a gray image is sliced into binary images, which have the same pixel value, and these images are encrypted by modified XOR rules with binary random images. The XORed images and the binary images respectively combined and converted into full phase images, called an encrypted image and a key image. For decryption, when the encrypted image and key image are used as inputs on optical elements, Practically due to limited controllability of phase range in optical elements, the original gray image cannot be efficiently reconstructed by these optical elements. Therefore, by decreasing the phase ranges of the encrypted image and key image using a phase-wrapping method and separating these images into low-level phase images using multi-phase separation, the gray image can be reconstructed by optical elements which have limited control range. The decrytion process is simply implemented by interfering a multiplication result of encrypted image and key image with reference light. The validity of proposed scheme is verified and the effects, which are caused by phase limitation in decryption process, is analyzed by using computer simulations.