파노라믹 3D가상 환경 생성을 위한 다수의 카메라 캘리브레이션

김세환,김기영,우운택 대한전자공학회 2004 電子工學會論文誌-CI (Computer and Information) Vol.41 No.4

본 논문에서는 영상기반 파노라믹 3D 가상 환경 (Virtual Environment: VE) 생성을 위해 회전하는 다수의 멀티뷰 카메라를 위한 캘리브레이션 방법을 제안한다. 일반적으로, 카메라 캘리브레이션 알고리즘은 카메라와 캘리브레이션 패턴 사이의 이 멀어질수록 획득되는 카메라 파라미터의 정확도가 상당히 저하되어 파노라마 영상 제작에는 부적합하다. 이러한 문제점을 극복하기 위해 멀티뷰 카메라의 렌즈간 그리고 회전하는 다수의 멀티뷰 카메라간의 기하학적인 상관 위치 관계를 이용하여 정확도를 높인다. 우선, Tsai의 캘리브레이션 알고리즘을 적용하여 획득된 카메라 파라미터를 카메라 렌즈간의 사전 기하 정보와 비교하여 그 오차에 기반한 인트라 카메라 캘리브레이션 (Intra-camera Calibration)을 수행한다. 그리고 가상 공간에 역투영된 3D point cloud에 ICP 알고리즘을 적용하여 인터 카메라 캘리브레이션 (Inter-camera Calibration)을 수행한다. 이를 확장하여, 다수의 카메라를 회전시켜 획득된 3D point cloud에 대해 기준 카메라의 위치를 중심으로 인터 카메라 캘리브레이션을 연속적으로 수행함으로써 회전하는 다수의 멀티뷰 카메라에 대한 캘리브레이션을 수행한다. 이와 같은 캘리브레이션 방법을 통해 중에서도 비교적 개선된 카메라 파라미터를 획득할 수 있기 때문에 파노라믹 3D 가상 환경을 생성하기 위한 정합과정에 사용할 수 있다. 또한, 실시간 3D 객체 추적 및 AR 응용 시스템 등의 다양한 AR 응용분야에 활용될 수 있다. In this paper, we propose a new camera calibration method for rotating multi-view cameras to generate image-based panoramic 3D Virtual Environment. Since calibration accuracy worsens with an increase in distance between camera and calibration pattern, conventional camera calibration algorithms are not proper for panoramic 3D VE generation. To remedy the problem, a geometric relationship among all lenses of a multi-view camera is used for intra-camera calibration. Another geometric relationship among multiple cameras is used for inter-camera calibration. First camera parameters for all lenses of each multi-view camera we obtained by applying Tsai's algorithm. In intra-camera calibration, the extrinsic parameters are compensated by iteratively reducing discrepancy between estimated and actual distances. Estimated distances are calculated using extrinsic parameters for every lens. Inter-camera calibration arranges multiple cameras in a geometric relationship. It exploits Iterative Closet Point (ICP) algorithm using back-projected 3D point clouds. Finally, by repeatedly applying intra/inter-camera calibration to all lenses of rotating multi-view cameras, we can obtain improved extrinsic parameters at every rotated position for a middle-range distance. Consequently, the proposed method can be applied to stitching of 3D point cloud for panoramic 3D VE generation. Moreover, it may be adopted in various 3D AR applications.

Robotic Camera Calibration to Maintain Consistent Percision of 3D Trackers

Junmin Baek,Gunwoo Noh,Joonho Seo 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.11

Camera calibration is essential for calculating camera parameters, and the parameters should be constant whenever the position tracker needs to be recalibrated. Manual camera calibration obtains a checkerboard image by tilting or positioning the checkerboard by hand. However, it makes difficult to obtain the same checkerboard images in every calibration, resulting in different camera parameters. Therefore, this study proposes robotic camera calibration to produce the constant camera parameters whenever the tracker needs to be calibrated. The robot arm moves the checkerboard according to the programmed positions and orientations so that the position tracker can obtain the same checkerboard image every calibration. Experiments were conducted to compare results of the manual and robotic camera calibrations. First, we compared the standard deviations of the intrinsic parameters and extrinsic parameters; the results show that robotic camera calibration produced the parameters with smaller standard deviations. We also compared the tracking precision of the cubic marker using manual and robotic camera calibration. As a result, the standard deviations of the tracking precision of cubic marker by the manual and the robotic camera calibration were 1.65 mm and only 0.35 mm, respectively. It reveals that the robotic camera calibration enables more precise and consistent tracking than the manual calibration.

Research on Camera Calibration in Football Broadcast Videos

Shouzhong Zhang 보안공학연구지원센터 2015 International Journal of u- and e- Service, Scienc Vol.8 No.3

A novel continuous camera calibration algorithm is proposed, which can address the calibration for non-goal area of soccer video. By considering the fact that the position of main camera is stable, a novel continuous camera calibration algorithm is proposed for soccer video analysis. There are two stages for calibration: the first stage addresses the calibration only for goal area and the position of camera is computed and recorded, and then the second stage can address calibration for any area including non-goal area where the camera position is given at first stage. Thus, the proposed algorithm can address the calibration for non-goal area of soccer video, which cannot be addressed by traditional calibration algorithms since the inadequate of calibration objects.

Detection of Calibration Patterns for Camera Calibration with Irregular Lighting and Complicated Backgrounds

Dong-Joong Kang,Jong-Eun Ha,Mun-Ho Jeong 대한전기학회 2008 International Journal of Control, Automation, and Vol.6 No.5

This paper proposes a method to detect calibration patterns for accurate camera calibration under complicated backgrounds and uneven lighting conditions of industrial fields. Required to measure object dimensions, the preprocessing of camera calibration must be able to extract calibration points from a calibration pattern. However, industrial fields for visual inspection rarely provide the proper lighting conditions for camera calibration of a measurement system. In this paper, a probabilistic criterion is proposed to detect a local set of calibration points, which would guide the extraction of other calibration points in a cluttered background under irregular lighting conditions. If only a local part of the calibration pattern can be seen, input data can be extracted for camera calibration. In an experiment using real images, we verified that the method can be applied to camera calibration for poor quality images obtained under uneven illumination and cluttered background.

무한원점의 성질을 이용한 포장 및 비포장 도로에서의 카메라 교정 파라메터 추정

정준익(Jeong Jun-ik),정명희(Jeong Myeong-Hee),노도환(Rho Do-Whan) 대한전기학회 2006 대한전기학회 학술대회 논문집 Vol.2006 No.10

In general. camera calibration has to be gone ahead necessarily to estimate a position and an orientation of the object exactly using a camera. Autonomous land system in order to run a vehicle autonomously needs a camera calibration method appling a camera and various road environment. Camera calibration is to prescribe the confrontation relation between third dimension space and the image plane. It means to find camera calibration parameters. Camera calibration parameters using the paved road and the unpaved road are estimated. The proposed algorithm has been detected through the image processing after obtaining the paved road and the unpaved road. There is able to detect easily edges because the road lanes exist in the paved road. Image processing method is two. One is a method on the paved road. Image is segmentalized using open, dilation, and erosion. The other is a method on the unpaved road. Edges are detected using blur and sharpening. So it has been made use of Hough transformation in order to detect the correct straight line because it has less error than least-square method. In addition to, this thesis has been used vanishing point' principle. an algorithm suggests camera calibration method using Hough transformation and vanishing point. When the algorithm was applied, the result of focal length was about 10.7[㎜] and RMS errors of rotation were 0.10913 and 0.11476 ranges. these have the stabilized ranges comparatively. This shows that this algorithm can be applied to camera calibration on the paved and unpaved road.

광학식 모션캡처를 위한 다중 카메라 보정 방법

신기영(Ki-Young Shin),문정환(Joung-H. Mun) 한국컴퓨터정보학회 2009 韓國컴퓨터情報學會論文誌 Vol.14 No.6

본 논문에서는 광학식 모션캡처 장비를 위한 다중 카메라 보정 방법을 제안한다. 이 방법은 DLT(Direct linear transformation) 알고리즘을 이용하여 7개의 마커가 있는 3축 보정틀의 영상을 획득하여 1차 카메라 보정을 한다. 그리고 2개의 마커가 있는 보정봉을 측정하고자 하는 영역에서 움직여서 2차 카메라 보정을 실시한다. 1차 카메라 보정에서는 카메라 보정뿐만 아니라 렌즈 왜곡 계수를 계산하여 2차 카메라 보정에서의 최적화를 위한 초기해로 사용한다. 2차 카메라 보정에서는 보정봉에 있는 마커사이의 거리가 일정하기 때문에 계산된 마커 거리와 실제 마커 거리의 차가 최소화 되도록 최적화를 수행한다. 제안한 방법에 의한 다중 카메라 보정 방법을 검증하기 위하여 재투영에러를 계산하였고 3축 보정틀에 있는 마커사이의 거리와 보정봉에 있는 마커사이의 거리를 계산하여 다른 상용장비의 값과 비교하였다. 3축 보정틀에 있는 마커를 복원하여 에러를 비교한 결과 평균오차가 상용장비의 1.7042mm에 비해 0.8765mm로 51.4% 수준으로 나타났고, 보정봉에 있는 마커를 복원하여 에러를 비교한 결과 상용장비의 평균에러 1.8897mm에 비해 2.0183mm로 0.1286mm 크게 나타났다. In this paper, the multi-camera calibration algorithm for optical motion capture system is proposed. This algorithm performs 1st camera calibration using DLT(Direct linear transformation} method and 3-axis calibration frame with 7 optical markers. And 2nd calibration is performed by waving with a wand of known length(so called wand dance} throughout desired calibration volume. In the 1st camera calibration, it is obtained not only camera parameter but also radial lens distortion parameters. These parameters are used initial solution for optimization in the 2nd camera calibration. In the 2nd camera calibration, the optimization is performed. The objective function is to minimize the difference of distance between real markers and reconstructed markers. For verification of the proposed algorithm, re-projection errors are calculated and the distance among markers in the 3-axis frame and in the wand calculated. And then it compares the proposed algorithm with commercial motion capture system. In the 3D reconstruction error of 3-axis frame, average error presents 1.7042mm(commercial system) and 0.8765mm(proposed algorithm). Average error reduces to 51.4 percent in commercial system. In the distance between markers in the wand, the average error shows 1.8897mm in the commercial system and 2.0183mm in the proposed algorithm.

큰 베이스라인을 가진 전방향 스테레오 카메라의 교정 방법

이강산(Kang-San Lee),강현수(Hyun-Soo Kang) 한국콘텐츠학회 2010 한국콘텐츠학회논문지 Vol.10 No.6

본 논문은 전방향 스테레오 카메라를 이용한 거리 측정을 위해 반드시 수행되어야 하는 전방향 카메라의 교정방법에 관해 기술한다. 전방향 스테레오 카메라의 교정에 있어서, 두 대의 전방향 카메라를 각각 독립적으로 교정하거나 두 대의 카메라의 베이스라인이 크지 않은 경우의 교정은 기존의 연구된 다양한 방법을 통해 가능하다. 그러나 전방향 스테레오 카메라를 이용하여 원거리를 측정하기 위해서는 베이스라인이 충분히 커야 하며, 충분히 큰 베이스라인은 두 대의 전방향 카메라를 동시에 교정하는 것이 매우 힘들다. 이는 두 대의 전방향 카메라에서 촬영된 교정을 위한 테스트패턴의 크기가 최소한 한 대의 전방향 카메라에서 매우 작은 크기로 나타나기 때문이다. 따라서 본 논문에서는 베이스라인이 큰 두 대의 전방향 카메라의 교정을 위한 방법을 제안하고 실험을 통해 검증한다. This paper presents a calibration method of an omnidirectional stereo camera which may be essentially performed for distance measurement to a certain point. In the calibration of the omnidirectional stereo camera, the independent calibrations of two cameras or the calibration of a stereo camera having the small baseline is feasible applying many methods studied in the past. However, the baseline should be large enough for long distance measurement by the omnidirectional stereo camera, since it is not easy to calibrate two cameras with a large baseline at the same time. It is because a test pattern for the calibration, which is simultaneously captured by two omnidirectional cameras, appears too small in at least one of the omnidirectional cameras. It causes inaccurate calibration. In this paper, therefore, we propose a calibration method of the omnidirectional stereo camera with a large baseline and empirically verify its feasibility.

구조광 방식 3차원 복원을 위한 간편한 프로젝터-카메라 보정 기술

박순용,박고광,Lei Zhang 한국정보처리학회 2010 정보처리학회논문지. 소프트웨어 및 데이터 공학 Vol.17 No.3

구조광(structured-light)을 이용한 3차원 복원 기술은 카메라 영상과 프로젝터 영상에서 구조광 코드(code)의 일치점을 탐색하고 그 점의 3차원 좌표를 획득하는 기술이다. 일치점의 3차원 좌표를 계산하기위해서는 카메라와 프로젝터의 보정(calibration)이 선행되어야 한다. 또한 복원된 3차원 형상의 정확도는 카메라와 프로젝터의 보정 결과에 영향을 받는다. 기존의 카메라-프로젝터 보정 기술은 고가의 장치를 사용하거나 복잡한 알고리즘을 사용하여 시간과 비용에 대한 효율성이 낮았다. 본 논문에서는 쉽고도 정밀한 카메라-프로젝터 보정 기술을 제안하고자 한다. 제안하는 기술은 복잡한 장치 또는 알고리즘이 필요치 않고 영상처리 기술로만 구현이 가능하기 때문에 3차원 형상복원의 효율성을 높일 수 있다. 두 종류의 카메라-프로젝터 장치에 대한 보정 실험 결과를 보였으며, 보정된 카메라와 프로젝터의 투영 오차 및 월드 기준점의 3차원 복원 오차를 측정하여 제안하는 알고리즘의 정밀도를 분석하였다. The structured-light 3D reconstruction technique uses a coded-pattern to find correspondences between the camera image and the projector image. To calculate the 3D coordinates of the correspondences, it is necessary to calibrate the camera and the projector. In addition, the calibration results affect the accuracy of the 3D reconstruction. Conventional camera-projector calibration techniques commonly require either expensive hardware rigs or complex algorithm. In this paper, we propose an easy camera-projector calibration technique. The proposed technique does not need any hardware rig or complex algorithm. Thus it will enhance the efficiency of structured-light 3D reconstruction. We present two camera-projector systems to show the calibration results. Error analysis on the two systems are done based on the projection error of the camera and the projector, and 3D reconstruction of world reference points.

Infrared Camera Calibration in the 3D Temperature Field Reconstruction

Sun Xiaoming,Wu Haibin,Wang Wei,Liubo,Cui Guoguang 보안공학연구지원센터 2016 International Journal of Multimedia and Ubiquitous Vol.11 No.6

In order to reconstruct the 3D temperature field based on the binocular vision system, we carry out a research on the calibration of the infrared camera. To start with, we make a calibration board which can be clearly identified by the infrared camera; then, with the help of OpenCV, we implement the calibration of two infrared cameras respectively and rectify the infrared images. According to the parameters obtained from the single infrared camera calibration, we accomplish the stereo calibration. The experimental results show that the average reprojecting error is below 0.14 pixels and when using the system to carry out a real measurement, the average error is 3.12%. The feasibility of the proposed calibration approach is verified, the experimental measurement results is close to the ground truth.

A Study on the Approach of the Structured Light Three-dimensional Measurement

Wang beiyi,,Yu xiaoyang,He baohua,Cai yingfu,Zhang jixun,Sun Xiaoming 보안공학연구지원센터 2015 International Journal of u- and e- Service, Scienc Vol.8 No.11

In order to establish the 3D Temperature Field based on structure light 3D measurement and cross-correlation registration. Infrared/Visible camera calibration method and heterologous images registration method were studied. First, according to infrared camera’s characteristics, the selection of calibration templates have been studied and the calibration of the infrared camera has been accomplished on the basis of planar calibration method; then, we simplified the two-step method based on the mature principle of structure light measurement; and the visible camera was calibrated; finally, use calibrated visible cameras to form structured light measurement system, and register the infrared image and visible image in the geometrical position. Experimental results show that: the relative error of measurement system is less than 0.3%;infrared and visible image’s alignment error in geometrical position is 0.0015 mm. and measurement systems have good reconstruction results for plane and curved ,and cross-correlation method has a good effect for heterrologous images registration.