Real Time Calibration Of Zoom Camera And Applied Research On Online Video Measurement

In order to measure the size of the defect in the cylindrical container with corrosive liquid accurately, the traditional contact measurement method has been difficult to meet the requirements of industrial production. Non-contact measurement method based on computer vision has been widely used in all aspects of social life, owing to the advantages such as consistency and high reliability of examination results, more accurate measurement data, suitable for harsh conditions and so on.This paper studies the key technologies of computer vision measurement mainly based on the actual needs and characteristics of video measurement project, and completes the measurement of the defects' size in the cylindrical vessel. In the project, the need is to obtain the actual size of the defect on the container, according to pictures of the cylindrical container captured by the camera under the different focuses and attitudes. And the only calibration objects are four laser spots formed on the cylindrical surface by laser beams, which are produced by laser guns around the camera. Thus, this paper analyzes the existing methods of camera calibration and proposes a real time calibration method of zoom camera based on laser spots. This method uses the idea of the direct linear transformation to construct the camera calibration model, and solves other unknown parameters in the camera calibration model according to the information of the laser spots on the defect image captured in real time under the situation that camera's principal point pixel coordinates are known. In the process of determining the pixel coordinates of camera's principal point, this paper focuses on the research of the vanishing point theory, gives a method how to determine camera principal point pixel coordinates using this theory when the camera horizontal grid spacing and vertical spacing is unequal, and determines the pixel coordinates of the camera's principal points by using this method in the laboratory environment. Finally, the calibration results are used in the measurement of defects on the cylindrical container. This paper introduces the measuring coordinate system which is constructed according to the actual testing cylinder, splitting cylindrical surface along the plane of the center line of the cylinder, transforming the measurement of defects from three-dimensional space to two-dimensional space, to solve the smallest rectangular envelope of the defect in the plane.In addition, using testing plate with defects verified calibration method and defect measurement model, which are proposed in this paper, under laboratory conditions. The result indicated that defect measurement can meet accuracy requirements through this method. This provides a guarantee for the method used in the video measurement project. It can realize automatic defect detection, adapt to a variety of harsh environment, and improve work efficiency.