• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1090-1093
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• 2004

In this paper, a problem of geometrically distorted images is considered. In particular, the paper discusses the detection of a watermark from a photographed image of the watermarked picture. The image is possibly obtained by using a digital camera. This watermark detection problem is made difficult by various geometric distortions added to the original picture through the printing and photographing processes. In particular, the paper focuses on the geometric distortion due to a projective transformation, as part of a camera 3D-to-2D imaging process. It is well-known that a cross ratio of collinear points is invariant under a perspective projection. By exploiting this fact, a projective-invariant digital watermarking technique is developed. By detecting the picture's corners, and the image center point at the intersection of two main diagonal lines, predefined cross ratios are used to compute the watermark embedded locations. From those identified embedding pixel locations, a watermark can be detected by performing a correlation between a watermark pattern and the image over those pixels. The proposed method does not require an inverse transformation on the distorted image, thus simplifying the detection process. Performance of the proposed method has been analyzed through computer experiments

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.420-425
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• 2004

Lee and Kang measured side-necking deformation near a crack-tip for CT specimen using Stereoscopic Digital Speckle Photography and Digital Image Correlation. In this work the same technique was applied to SENB specimen. We happened to find that the deformation shape of the side-necking is similar to the one of plastic region estimated by McClictock using slip line theory. Based on volume constancy of plastic deformation as well as this finding, it is expected that a linear relationship holds between the volume of plastic deformation region and the one of side-necking upon the lateral surface of a specimen. To prove the idea, a preliminary study has been performed using 3-D finite element method on a model with modified boundary layer formulation. As the result, it is shown that the idea works well with acceptable error.

• The KIPS Transactions:PartB
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• v.10B no.4
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• pp.367-372
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• 2003

The existing watermarking techniques for copyright protection of a digital image are fragile in geometric distortion and it is hard to detect whether it was manipulated artificially. In this paper, we proposed the new copyright protection system that can authorize a digital mage and :an embed or extract a robust watermark in a artificial manipulation in order to solve these problems. In a watermarking part, the proposed a watermarking technique embeds a watermark in a phase component after a Complex Wavelet Transform (CWT) with an original image, and a watermark is extracted from an watermarked image by stages. A copyright about an image can be insisted on than a threshold after comparing a correlation of an original watermark with an extracted watermark if large. In an authentication part of a digital image, EZW (Embedded Zerotree Wavelet) is used, and an authentication cord of an watermarked image is generated. An authentication code of an image to have been distribute to is compared with a generated authentication cord, and artificial operation isn´t than a threshold if large. The proposed copyright protection system through performance evaluation display that it was robust in geometric distortion and a artificial operation was able to be detected.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10C
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• pp.933-941
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• 2006

In this paper, we proposed an efficient coding method for digital hologram (fringe pattern) acquired by a CCD camera or by computer generation using multi-view prediction technique and MPEG video compression standard technique. It proceeds each R, G, or B color component separately. The basic processing unit is a partial image segmented into the size of $N{\times}N$. Each partial image retains the information of the whole object. This method generates an assembled image for a row of the segmented and frequency-transformed partial images, which is the basis of the coding process. That is, a motion estimation and compensation technique of MPEG is applif:d to the reconstructed images from the assembled images with the disparities found during generation of assembled image and the original partial images. Therefore the compressed results are the disparity of eachpartial image to form the assembled image for the corresponding row, assembled image, and the motion vectors and the compensated image for each partial image. The experimental results with the implemented algorithm showed that the proposed method has NC (Normal Correlation) values about 4% higher than the previous method, by which ours has better compression efficiency. Consequently, the Proposed method is expected to be used effectively in the application areas to transmit the digital hologram data. can be identified in comparison with the previous researches and commercial IPs.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.9
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• pp.877-882
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• 2011

In this paper, thermal deformation of a double ring structure using digital image correlation technique (DIC) was measured. The double ring structure consisted of two parts; the inner ring was aluminium which had a large thermal expansion coefficient and the outer ring was titanium which had a small thermal expansion coefficient. We heated the double ring structure from $50^{\circ}C$ to $200^{\circ}C$ in a chamber and at the same time, two cameras captured surface images of the double ring structure. Initially, there was a 21 ${\mu}m$ gap between the inner ring and outer ring. The gap was closed at around $80^{\circ}C$ and after that, two rings expanded together. In order to compare the experimental results with analysis results, a finite element analysis was performed using ANSYS. The results of DIC measurement and ANSYS analysis were compared and agreed well.

• Computers and Concrete
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• v.31 no.5
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• pp.385-394
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• 2023

Displacement is an important element for evaluating the stability and failure mechanism of hydraulic structures. Digital image correlation (DIC) is a useful technique to measure a three-dimensional displacement field using two cameras without any contact with test material. The objective of this study is to evaluate the behavior of stacked geotextile tubes using the DIC technique. Geotextile tubes are stacked to build a small-scale temporary dam model to exclude water from a specific area. The horizontal and vertical displacements of four stacked geotextile tubes are monitored using a dual camera system according to the upstream water level. The geotextile tubes are prepared with two different fill materials. For each dam model, the interface layers between upper and lower geotextile tubes are either unreinforced or reinforced with a cementitious binder. The displacement of stacked geotextile tubes is measured to analyze the behavior of geotextile tubes. Experimental results show that as upstream water level increases, horizontal and vertical displacements at each layer of geotextile tubes initially increase with water level, and then remain almost constant until the subsequent water level. The displacement of stacked geotextile tubes depends on the type of fill material and interfacial reinforcement with a cementitious binder. Thus, the proposed DIC technique can be effectively used to evaluate the behavior of a hydraulic structure, which consists of geotextile tubes.

• Journal of Institute of Convergence Technology
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• v.5 no.1
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• pp.7-12
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• 2015

Sheet metal formability can be defined as the ability of metal to deform without necking or fracture into desired shape. Every sheet metal can be deformed without failure only up to a certain limit, which is normally known as forming limit curve(FLC). In this paper, the dome stretching tests and tensile tests have been performed to obtain forming limit curve of aluminum alloy. During the experiment, failure strain is measured using digital image correlation(DIC) method. DIC method is a whole-field measurement technique that acquires surface displacements and strains from images information which characterized a random speckle as intensity grey levels. Recently years, this DIC method is being developed and used increasingly in various research. DIC results demonstrated the usefulness and ability to determine a strain.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.688-694
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• 2002

As a tool for strain measurement to work with screw driven or hydraulic material test systems, in which mechanical vibration is inherent, SSDG(Speckle Strain/Displacement Gage), ESP(Electronic Speckle Photography) and its 3-dimension version SDSP are investigated for the theory and practical appliance. Through tension test of steel strips, their validity and shortcomings are examined. As the results, it has been shown that, although SSDG and ESP provide direct measurement of in-plane strain in one direction, they are so sensitive to the out-plane displacement. On the other hand, SDSP which is aided with DIC (Digital Image Correlation) technique to trace the movement of the speckles provides not only in-plane 2-dimensional displacement field, but also out-of-plane displacement simultaneously. However, because the DIC is time-consuming, not automated yet and it needs post-processing to evaluate strain from the displacement field, SDSP appears to be not adequate as a real time sensor.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.5C
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• pp.406-414
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• 2005

The necessity for a technique to protect intellectual property of a digital content has been increasing, especially for the image/video contents which are the most favorite because of their high information-intensive property. According to this demand, this paper proposed a digital watermarking algorithm, which is recognized as the most promising technique. This algorithm targets MPEG compression system and the watermarking process is to be performed during the compression process. It inserts watermark only in Y components of I-frames. Experimental results showed that the proposed method satisfied both imperceptibility and robustness against various attacks. The PSNR difference between the compressed images(the average compression ratio was about 27:1 with Y:Cb:Cr=4:2:0 color format for TM5-based compression) with and without watermarking was only 1.8dB ($4.2\%$). In each case that the resulting image after an attack was reusable the normalized correlation between the extracted watermark and the original one was above 0.8.

• Journal of the Korea Society of Computer and Information
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• v.23 no.4
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• pp.33-39
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• 2018

In this paper, we propose a describes how to detect a false iris image by inserting watermark into a iris image. The existing method, which inserts the watermark into the entire iris image to detect a fake iris, has a problem that can evade it by segmenting iris region of an iris image. The purpose of overcoming the problem, this paper proposes a new fake iris detection technique based on digital watermark. It first searches a central point of an iris image, divide the image into blocks with respect to the point. executes Discrete Cosine Transform, inserts watermark into the blocks, and then verifies an iris image using NC(Normalized Correlation). In the experiments, we confirm the robustness for attacks - crop and JPEG.