• Progress in Medical Physics
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• v.10 no.2
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• pp.73-81
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• 1999

Scatter correction for single photon emission computed tomography (SPECT) plays an important role to improve image quality and quantitation. The purpose of this study was to investigate three scatter correction methods using Monte Carlo simulation. Point source and Jaszack phantom filled with Tc-99m were simulated by Monte Carlo code, SIMIND. For scatter correction, we applied three methods, Compton window (CW) method, triple window (TW) method, and dual photopeak window (DPW) method. Point sources located at various depths along the center line within a 20-cm phantom were simulated to calculate the window ratios and corresponding scatter fractions by evaluating the polynomial coefficients for DPW method. Energy windows were located in W$_1$=92-125 keV, W$_2$=124-126 keV, W$_3$=136-140 keV, W$_4$=140-141 keV, and W$_{5}$=154-156 keV. The results showed that in Jaszack phantom with cold sphere and hot sphere, the TW gave the closest contrast and percentage recovery to the ideal image, respectively, while CW overestimated and DPW underestimated the contrast of ideal one. All three scatter correction methods showed an improved image contrast. In conclusion, scatter correction is essential for improving image contrast and accurate quantification. The choice of scatter correction method should be made on the basis of accuracies and ease of implementation.

• Investigative Magnetic Resonance Imaging
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• v.13 no.1
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• pp.22-30
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• 2009

Purpose : Patient motion during magnetic resonance (MR) imaging is one of the major problems due to its long scan time. Entropy based post-processing motion correction techniques have been shown to correct motion artifact effectively. One of main limitations of these techniques however is its long processing time. In this study, we propose several methods to reduce this long processing time effectively. Materials and Methods : To reduce the long processing time, we used the separability property of two dimensional Fourier transform (2-D FT). Also, a computationally light metric (sum of all image pixel intensity) was used instead of the entropy criterion. Finally, partial Fourier reconstruction, in particular the projection onto convex set (POCS) method, was combined thereby reducing the size of the data which should be processed and corrected. Results : Time savings of each proposed method are presented with different data size of brain images. In vivo data were processed using the proposed method and showed similar image quality. The total processing time was reduced to 15% in two dimensional images and 30% in the three dimensional images. Conclusion : The proposed methods can be useful in reducing image motion artifacts when only post-processing motion correction algorithms are available. The proposed methods can also be combined with parallel imaging technique to further reduce the processing times.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.5C
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• pp.632-641
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• 2004

In this paper, a new intermediate view reconstruction method employing a stereo image rectification algorithm by which an uncalibrated input stereo image can be transformed into the calibrated one is suggested and its performance is analyzed. In the proposed method, feature point are extracted from the stereo image pair though detection of the corners and similarities between each pixel of the stereo image. And then, using these detected feature points, the moving vectors between stereo image and the epipolar line is extracted. Finally, the input stereo image is rectified by matching the extracted epipolar line between the stereo image in the horizontal direction and intermediate views are reconstructed by using these rectified stereo images. From some experiments on synthesis of the intermediate views by using three kinds of stereo image; a CCETT's stereo image of 'Man' and two stereo images of 'Face' ＆ 'Car' captured by real camera, it is analyzed that PSNRs of the intermediate views reconstructed from the calibrated image by using the proposed rectification algorithm are improved by 2.5㏈ for 'Man', 4.26㏈ for 'Pace' and 3.85㏈ for 'Car' than !hose of the uncalibrated ones. This good experimental result suggests a possibility of practical application of the unposed stereo image rectification algorithm-based intermediate view reconstruction view to the uncalibrated stereo images.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.155.2-155.2
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• 2012

CTIO 4m 및 CTIO 1m 망원경으로 Westerlund 2의 UBVI 관측을 수행하여, CTIO 4m SDSS $u$ filter의 적색광누출 현상을 발견하였고 그 영향을 분석하였다. 적색광누출 현상은 filter의 투과함수가 설계와는 달리 장파장 영역에서 투과 존재하는 현상으로, CTIO 4m SDSS $u$ filter의 경우 B-V>1.4, V-I>2.0에서 그 영향이 나타나기 시작한다. SDSS $u$ filter의 적색광누출 현상은 별의 고유색지수와 상관없이 관측된 색지수가 클수록 영향이 크며, $B-V{\leq}1.8$, $V-I{\leq}2.8$의 범위에서는 보정이 가능하다. CTIO 1m B filter에서는 성간소광을 받지 않은 별과 성간소광을 많이 받은 별의 표준계변환 결과, $B_{CTIO1m}=B_{Standard}-0.055{\times}E(V-V)$에 해당하는 차이를 보였다. 이러한 차이는 CTIO 1m B filter의 투과함수의 단파장 쪽 날개부분이 표준 Johnson B filter에 비하여 단파장 쪽으로 많이 치우쳐있기 때문으로 보인다. 특히 Ballmer jump에 해당하는 파장인 370 nm에서 filter의 최대투과율에 비하여 32.2%에 달하는 투과율을 보이는데, 이는 Bessell B filter의 3.1%에 비하여 매우 큰 값이다. CTIO 1m 망원경의 Y4KCam CCD에서는 포화된 화소에 의한 crosstalk 뿐 아니라 포화되지 않은 화소에 의한 crosstalk 현상도 보였다. 짧은 노출을 준 영상에서는 5000 ADU 이상에서는 육안에 의한 crosstalk 확인이 가능하며, 포화되지 않은 밝은 별에 의한 crosstalk을 확인하지 않고 측광할 경우 백색왜성으로 오인할 가능성이 있으므로 측광 과정에서 좌표를 통하여 확인할 필요가 있다.

• Progress in Medical Physics
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• v.10 no.3
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• pp.125-131
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• 1999

T$_1$/T$_2$ weighted images are being used to give the characteristic contrast among the various tissues and the norma;/abnormal tissues. Abnormalities in tissues, in general, accompany the biochemical changes and eventually structural ones in which results in the change in T$_1$ and T$_2$ relaxation times of water protons. It has been suggested that the mapping of T$_1$/T$_2$ values may serve as a possible tool for the quantitative evaluation of the degree of abnormality. On reconstructing T$_1$/T$_2$ maps(or any other MR parametric map), only corresponding variables are to be varied, such as TE for T$_2$, TI or TR for T$_1$ and b-factor for diffusion images. But often the receiver gain is taken for the optimal usage of A/D converter, so that the set of the image data has different receiver gain. It must be corrected before any attempt to reconstruct the maps. Here we developed method of correcting receiver gain variation effect, using the standard deviation of noise on individual image. The resultant T$_1$ and T$_2$ values were very comparable to the other reported values.

• Korean Journal of Remote Sensing
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• v.27 no.2
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• pp.141-150
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• 2011

Precise image-to-image registration is required to process multi-sensor data together. The purpose of this paper is to develop an algorithm that register between high-resolution optical and SAR images using linear features. As a pre-processing step, initial alignment was fulfilled using manually selected tie points to remove any dislocations caused by scale difference, rotation, and translation of images. Canny edge operator was applied to both images to extract linear features. These features were used to design a cost function that finds matching points based on their similarity. Outliers having larger geometric differences than general matching points were eliminated. The remaining points were used to construct a new transformation model, which was combined the piecewise linear function with the global affine transformation, and applied to increase the accuracy of geometric correction.

• Journal of the Korean Association of Geographic Information Studies
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• v.18 no.4
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• pp.68-80
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• 2015

To increase the utilization of the KOrea Multi-Purpose SATellite(KOMPSAT) series imagery being developed pursuant to the national space development program, high quality images with enhanced locational accuracy should be created through standardized post-processing processes. In the present study, using the Value-Added Processing System(VAPS) constructed for the post-processing of KOMPSAT imagery, location correction experiments were conducted using KOMPSAT-2 and -3 imagery from domestic and overseas regions. First, 50 pieces from each of KOMPSAT-2 imagery were selected from South Korean and North Korean regions, and modeling was conducted using GCP Chips. According to the results, the Root Mean Square Errors(RMSE) for South Korea and North Korea were 1.59 pixels and 2.04 pixels, respectively, and the locational accuracy of ortho mosaic imagery using check points were 1.33m(RMSE) and 1.90m(RMSE), respectively. Meanwhile, in the case of overseas regions for which GCP could not be easily obtained, the improvement of locational accuracy could be identified through image corrections using Open Street Map(OSM). The VAPS and reference materials used in the present study are expected to be very useful in constructing a precise image DB for entire global regions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.7C
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• pp.687-696
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• 2009

The motion compensated interpolation method is widely used to increase video frame rates. Especially, the bilateral motion estimation technique provides the improved results, since it doesn't make the overlapping and missing blocks in the interpolated frame. However, the motion vectors, which are obtained by the bilateral motion estimation, sometimes require further correction. In this paper, we propose the efficient motion vector.correction method for the bilateral motion estimation technique. By comparing the motion vectors of neighboring blocks and searching the new motion vector after merging the neighboring blocks, the erroneous motion vectors are efficiently corrected. It is shown that the proposed method provides better results, compared with the conventional methods.

• Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
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• 2003.04a
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• pp.531-536
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• 2003

In this paper, a camera modeling method that utilizes ephemeris data and imaging geometry is presented. The proposed method constructs a mathematical model only with parameters that are contained in the leader file and does not require any ground control points for model construction. Control points are only needed to eliminate geolocation error of the model that is originated from errors in the parameters that are used in model construction. With few (one or two) of control points, RMS error of less than pixel size can be obtained and control points are not necessarily uniformly distributed over the entire scene. This advantage is crucial in large project and will enable to reduce project cost dramatically.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.40 no.1
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• pp.19-29
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• 2003

This paper proposes a CMOS readout circuit for uncooled micro-bolometer arrays adopting a four-point step calibration technique. The proposed readout circuit employing an 11b analog-to-digital converter (ADC), a 7b digital-to-analog converter (DAC), and an automatic gain control circuit (AGC) extracts minute infrared (IR) signals from the large output signals of uncooled micro-bolometer arrays including DC bias currents, inter-pixel process variations, and self-heating effects. Die area and Power consumption of the ADC are minimized with merged-capacitor switching (MCS) technique adopted. The current mirror with high linearity is proposed at the output stage of the DAC to calibrate inter-pixel process variations and self-heating effects. The prototype is fabricated on a double-poly double-metal 1.2 um CMOS process and the measured power consumption is 110 ㎽ from a 4.5 V supply. The measured differential nonlinearity (DNL) and integrat nonlinearity (INL) of the 11b ADC show $\pm$0.9 LSB and $\pm$1.8 LSB, while the DNL and INL of the 7b DAC show $\pm$0.1 LSB and $\pm$0.1 LSB.