• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.58-59
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• 2003

We propose the optical encryption system using two divided image to hide the original image and a joint transform correlator. The encryption procedure is performed by the Fourier transform of the product of each phase encoded image (divided phase images) and the same random phase image which is generated by computer processing. An autocorrelation term of joint transform correlator contributes to decrypt the original image. This system will be used in optical certification.

• Korean Journal of Optics and Photonics
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• v.14 no.6
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• pp.630-635
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• 2003

We propose an encryption method using visual cryptography and virtual phase images. In the encryption process, the original image is shared by virtual images and the decryption key image. We multiply the virtual phase images with each complex image, which has the constant value of its sum after performing the phase modulation of the virtual images and the decryption key. The encryption cards are made by Fourier transforming the multiplied images. It is possible to protect information about the original image because the cards do not have any information from the original image. To reconstruct the original image, all the encryption cards are placed on each path of a Mach-Zehnder interferometer and then the lights passing through them are summed. Since the summed image is inverse Fourier transformed by a Fourier lens, the phase image is multiplied with the decryption key and the output image is obtained in the form of intensity on the CCD plane. Computer simulations show a good performance of the pro-posed optical security system.

• Current Optics and Photonics
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• v.4 no.2
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• pp.115-120
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• 2020

A novel method is proposed for controlling the distance of an image plane in Fourier holograms using varifocal electric-field-driven liquid-crystal (ELC) lenses. Phase Fresnel lenses are employed to reduce the thickness and response time of the ELC lenses. The voltages applied to the electrodes of the ELC Fresnel lens are adjusted so that the lens has the same retardation distribution as an ideal lens. The focal length can be controlled by changing the retardation distribution with the applied voltages. Simulations were conducted for the image reconstruction of Fourier holograms with various focal lengths of the ELC Fresnel lenses. The simulation results indicate that the distance of the image plane can be properly controlled with the varifocal ELC Fresnel lens.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.04a
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• pp.106-109
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• 2009

Recently, image matching becomes important in Computer Aided Diagnosis (CAD) due to the huge amount of medical images. Specially, texture feature is useful in medical image matching. However, texture features such as co-occurrence matrices can't describe well the spatial distribution of gray levels of the neighborhood pixels. In this paper we propose a frequency domain-based texture feature extractor that describes the local spatial distribution for medical image retrieval. This method is based on 2D Local Discrete Fourier transform of local images. The features are extracted from local Fourier histograms that generated by four Fourier images. Experimental results using 40 classes Brodatz textures and 1 class of Emphysema CT images show that the average accuracy of retrieval is about 93%.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.8
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• pp.67-73
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• 2015

In a distribution of digital image, there is a serious problem that is the image alteration by a forger. For the problem solution, this paper proposes the forensic decision algorithm of a median filtering (MF) image using the feature vector based on a coefficient of variation (c.v.) of Fourier transform. In the proposed algorithm, we compute Fourier transform (FT) coefficients of row and column line respectively of an image first, then c.v. between neighboring lines is computed. Subsquently, 10 Dim. feature vector is defined for the MF detection. On the experiment of MF detection, the proposed scheme is compared to MFR (Median Filter Residual) and Rhee's MF detection schemes that have the same 10 Dim. feature vector both. As a result, the performance is excellent at Unaltered, JPEG (QF=90), Down scaling (0.9) and Up scaling (1.1) images, and it showed good performance at Gaussian filtering ($3{\times}3$) image. However, in the performance evaluation of all measured items of the proposed scheme, AUC (Area Under ROC (Receiver Operating Characteristic) Curve) by the sensitivity and 1-specificity approached to 1 thus, it is confirmed that the grade of the performance evaluation is rated as 'Excellent (A)'.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.8
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• pp.1897-1904
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• 1996

This study intends to extract the efficient spectrum characteristics of the fingerpriint image in the fourier domain and to apply them for image enhancement. In order to effectively acquire the spectrum characteristics of the fingerprint in the fourier domain, I set up a 1*64 window as a processing unit and, combining various kinds of the record and overlap lengths, made the power spectrum density estimate for each of those combinations. each spectrum characeristic acquired was applied to a re-synthesis process of the fingerprint image, and, through comparisons and evaluations of the resultant images, an improved gray scale image could be obtained. The validity of this algorithm could be confirmed by the comparison and evaluation fo the binary images which were grained on the established method and the one I used in this experiment.

• Journal of the Optical Society of Korea
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• v.19 no.2
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• pp.149-153
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• 2015

A digital micro-mirror device (DMD) has the potential to modulate an incident wave with high speed, and the application for holographic display has been studied by many researchers. However, the quality of reconstructed image isn't good in comparison with that from a gray-scale amplitude-only hologram since it is a binary amplitude-only spatial light modulator (SLM). In this paper, we suggest a method generating a set of binary holograms to improve the quality of the reconstructed image. Here, we are concerned with the case for which the object plane is positioned at the Fourier domain of the plane of the SLM. In this case, any point in the Fourier plane is related to all points in the hologram. So there is a chance to generate a set of binary holograms illuminated by incident wave with constant optical power. Moreover, we find an interesting fact that the quality of reconstructed image is improved when the spatial frequency bandwidth of the binary hologram is limited. Therefore, we propose an iterative segmentation algorithm generating a set of binary holograms that are designed to be illuminated by the wave with constant optical power. The feasibility of our method is experimentally confirmed with a DMD.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.6
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• pp.955-963
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• 2008

In this paper, we propose an improved practical encryption and fault-tolerance decryption method using a non-negative value key and random function obtained with a white noise by using iterative phase wrapping method. A phase wrapping operating key, which is generated by the product of arbitrary random phase images and an original phase image. is zero-padded and Fourier transformed. Fourier operating key is then obtained by taking the real-valued data from this Fourier transformed image. Also the random phase wrapping operating key is made from these arbitrary random phase images and the same iterative phase wrapping method. We obtain a Fourier random operating key through the same method in the encryption process. For practical transmission of encryption and decryption keys via Internet, these keys should be intensity maps with non-negative values. The encryption key and the decryption key to meet this requirement are generated by the addition of the absolute of its minimum value to each of Fourier keys, respectively. The decryption based on 2-f setup with spatial filter is simply performed by the inverse Fourier transform of the multiplication between the encryption key and the decryption key and also can be used as a current spatial light modulator technology by phase encoding of the non-negative values. Computer simulations show the validity of the encryption method and the robust decryption system in the proposed technique.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.165-168
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• 2004

This paper propose a target tracker using phase correlation. The tracker consist of a pre-processing module, a translation estimation module based on phase correlation, a fine motion estimation module applied when confidence rate could not fulfill a threshold value and a reference image update module. The fine motion estimation module measure the shift, rotation and scale of input image compared to reference using Fourier-Mellin transform. Proposed tracker was tested its accuracy and robustness using some real indoor and outdoor image sequences.

• Proceedings of the IEEK Conference
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• 2001.06b
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• pp.63-66
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• 2001

In this paper a binary image encryption technique and decryption system based on a joint transform correlator (JTC) are Proposed. In this method, a Fourier transform of the encrypted image is used as the encrypted data and a Fourier transform of the random phase is used as the key code. The original binary image can be reconstructed on a square law device, such as a CCD camera after the joint input is inverse Fourier transformed. The proposed encryption technique does not suffer from strong auto-correlation terms appearing in the output plane. Based on computer simulations, the proposed encryption technique and decoding system were demonstrated as adequate for optical security applications.