• Journal of the Institute of Electronics Engineers of Korea SP
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• v.48 no.6
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• pp.115-123
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• 2011

Most of cameras being used in practice induce lens distortion; the amount of distortion depends on the specific applications as well as the camera cost. Up to now, many methods of lens distortion correction have relied on invariant properties of projective geometry to find distortion parameters. A common property is "the straight line in scene is straight line in image". However, if the straight lines are also parallel together, the previous works have missed this restriction in determining lens distortion parameters. In this paper, we propose a method that leads to guarantee of the restrictions simultaneously for the determination. Therefore, corrected image will close to an ideal image taken by the pinhole camera model. The effectiveness of the proposed method is verified by our experiments on both synthetic images and real images.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.151-151
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• 2020

표면영상유속측정법은 영상을 이용한 비접촉식 유속 측정 방법으로 카메라 외에 별도로 고가의 장비를 구매할 필요가 없을 뿐 아니라 현장 상황을 영상으로 확인할 수 있기 때문에 현장조사인력이 필요 없어 경제적이고, 안전하다는 장점을 갖고 있는 하천 유속 측정 방법이다. 표면영상유속측정법은 일반적으로 상호상관법을 이용하여 수표면을 촬영한 연속된 두 영상에서 입자군의 명암값 분포를 계산하여 입자군의 변위를 계산하고 이를 두 영상 사이의 시간 간격으로 나누어 입자군의 이동 속도를 산정하는 방법이다. 따라서 표면영상유속측정법으로 산정한 유속의 정확도를 높이기 위해서는 영상 내 두 입자군의 변위를 정확하게 계산하는 것이 무엇보다 중요하다. 즉, 분석하고자 하는 영상의 물리거리를 정확하게 계산할 수 있어야 한다. 카메라를 이용하여 실제 하천 영상을 촬영한 영상은 카메라 렌즈에 의한 왜곡이 필연적으로 발생하게 되고 이는 영상 내의 변위 산정 시에도 영향을 미친다. 특히 드론을 활용하여 넓은 하천 영역을 촬영할 경우 카메라 렌즈에 의한 왜곡은 실제 물리 변위 계산 정확도에 큰 영향을 미치게 된다. 이에 본 연구에서는 카메라 왜곡이 영상 내 변위 산정 결과의 정확도에 미치는 영향을 분석하였다. 연구 결과 카메라 렌즈 왜곡은 영상 중심에서 방사방향으로 점점 크게 발생하고 왜곡 정도는 비선형적으로 나타났으며, 변위 측정 오차는 영상의 중앙부에서는 거의 차이가 없었으며, 영상 외곽부에서 최대 오차가 발생하는 것으로 나타났다. 그리고 카메라 렌즈 왜곡 보정을 실시하게 되면 영상 전체적으로 변위측정 오차는 모두 제거할 수 있는 것으로 확인하였다. 따라서 카메라 렌즈 왜곡 보정을 실시하여 표면영상유속 측정 결과의 정확도를 개선할 수 있는 것으로 나타났다. 향후 카메라 렌즈 왜곡 보정을 실시한다면 하천의 표면유속을 보다 정확하게 측정할 수 있을 것으로 기대한다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.3
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• pp.597-602
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• 2013

In this paper, the lens module of mega pixel type was designed for barrel distortion calibration due to the barrel distortion of ultra wide angle. And the performance of this camera module was improved with the images from wide dynamic range 2 megapixel CMOS image sensor.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.27 no.3
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• pp.323-330
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• 2009

The demand that we are monitoring security and crime of the urban facilities is increasing recently, but the using CCTV devices are expensive. In this research, we enlarge the angle of view using the Fish-eye Lens and the Photogrammetry, the efficiency of monitoring enhance. First, we carry out the calibration of the Fish-eye Lens indoors, we calculate the correction parameters, and then covert the original image-point to new image-point correcting distortion. Second, the correction program with the correction parameters can obtain the real-time correcting image. Lastly, for authorization the developed program we compare correcting-image with scanning-imge, it is showed the RMSE is 3.2pixel.

• Journal of the Korea Society of Computer and Information
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• v.14 no.4
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• pp.31-38
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• 2009

Lens distortion is inevitable phenomenon in machine vision system. More and more distortion phenomenon is occurring in order to choice of lens for minimizing cost and system size. As shown above, correction of lens distortion is critical issue. However previous lens correction methods using camera model have problem such as nonlinear property and complicated operation. And recent lens correction methods using neural network also have accuracy and efficiency problem. In this study, I propose new algorithms for correction of lens distortion. Distorted image is divided based on the distortion quantity using k-means. And each divided image region is corrected by using neural network. As a result, the proposed algorithms have better accuracy than previous methods without image division.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.26 no.2
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• pp.103-110
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• 2008

General lens, widely using in Photogrammetry, has narrow view, and have to adjust "Image-Registration Method" after obtain images and it need cost; economic, period of time. Recent days, there is various study that use wide-angle lens, usually for robotics field, put to practical use in photogrammetry instead of general lens. In this studies, distortion tendency of wide-angle lens and utilize the correction techniques suitable to wide-angle lens by the existing photographic survey methods. After carrying out the calibration of the wide-angle lens, we calculated the correction parameters, and then developed the method that convert the original image-point to new image-point correcting distortion. For authorization the developed algorithm, we had inspection about shape and position; there are approximately 2D RMSE of 3 pixel, cx = 2, and cy = 3 different.

• The KIPS Transactions:PartB
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• v.10B no.4
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• pp.373-380
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• 2003

Most of low cost digital cameras reveal relatively high lens distortion. The purpose of this research is to compensate the degradation of image quality due to the geometrical distortion of a lens system. The proposed method consists of two stages : calculation of a lens distortion coefficient by a simplified version of Tsai´s camera calibration and subsequent image warping of the original distorted image to remove geometrical distortion based on the calculated lens distortion coefficient. In the lens distortion coefficient calculation stage, a practical method for handling scale factor ratio and image center is proposed, after which its feasibility is shown by measuring the performance of distortion correction using a quantitative image quality measure. On the other hand, in order to apply image warping via inverse spatial mapping using the result of the lens distortion coefficient calculation stage, a cubic polynomial derived from an adopted radial distortion lens model must be solved. In this paper, for the purpose of real-time operation, which is essential for embedding into an information device, an approximated solution to the cubic polynomial is proposed in the form of a solution to a quadratic equation. In the experiment, potential for real-time implementation and equivalence in performance as compared with that from cubic polynomial solution are shown.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.49 no.4
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• pp.16-22
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• 2012

In this paper, we present spiral pattern which suits for optical simulator to calibrate fisheye lens and compensate geometric distortion. Using spiral pattern, we present calibration without mathematical modeling in advance. Proposed spiral pattern used to input image of optical simulator. Using fisheye lens image, we calibrate a fisheye lens by matching geometrically moved dots to corresponding original dots which leads not to need mathematical modeling. Proposed algorithm calibrates using dot matching which matches spiral pattern image dot to distorted image dot. And this algorithm does not need modeling in advance so it is effective. Proposed algorithm is enabled at processing of pattern recognition which has to get the exact information using fisheye lens for digital zooming. And this makes possible at compensation of geometric distortion and calibration of fisheye lens image applying in various image processing.

• Journal of Korean Society for Geospatial Information Science
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• v.19 no.4
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• pp.55-63
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• 2011

Having a wide angle of view, a fisheye lens is useful for obtaining images of the inside wall of a tunnel. A circular fisheye tunnel image can be transformed into a familiar rectangular image by applying the concept of cylindrical projection. This projection transformation causes several types of distortions in the projected image. This paper discusses the distortion on the boundary lines between smoothly curved wall and flat ground. We analyzed the cause of this boundary distortion, developed transformation model, and derived a correction formular. A distortion correction software programmed in Visual C++ applied to projected image. Consequently, boundary-corrected image could be obtained. Research into other distortions of projected image will helpful in obtaining tunnel image that resembles real tunnel from fisheye tunnel image.

• 한국HCI학회:학술대회논문집
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• 2009.02a
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• pp.601-605
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• 2009

Due to the fact that fish-eye lens can provide super wide angles with the minimum number of cameras, field-of-view over 180 degrees, many vehicles are attempting to mount the camera system. Camera calibration should be preceded, and geometrical correction on the radial distortion is needed to provide the images for the driver's assistance. However, vehicle fish-eye cameras have diagonal output images rather than circular images and have asymmetric distortion beyond the horizontal angle. In this paper, we introduce a camera model and metric calibration method for vehicle cameras which uses feature points of the image. And undistort the input image through a perspective projection, where straight lines should appear straight. The method fitted vehicle fish-eye lens with different field of views.