Research On Measurement Technology Of Wide Field Of View Multi-CCD Camera

LCD(Liquid Crystal Display)has become the leading product of flat panel display in the world with its excellent display performance.As the most intuitive visual perception factor for consumers,LCD display uniformity is an important factor affecting its quality level.With the rapid development of LCD in large size,high resolution and large quantities,the use of optical devices such as brightness meter and illuminometer cannot measure LCD pixel by pixel quickly and accurately,which significantly restricts the quality evaluation,de-Mura correction of LCD,etc.CCD camera can quickly measure the brightness,chromaticity and other information of the object.Based on the principle of camera and optical measurement theory,this design studies the application of CCD camera in LCD measurement.Aiming at the distortion phenomenon of the measured image collected by the CCD camera and the limitation of the field of view and resolution of the single camera,the measurement accuracy could be improved by rectifying the distortion of the image,and the measurement accuracy is improved by splicing multi-CCD cameras to obtain the display information of large-scale and high-resolution LCD.The main contents of this paper are as follows:1)The composition and working principle of the wide-field multi-CCD camera measurement system are introduced.According to the characteristics of the CCD camera,the imaging model of the CCD camera is analyzed.The position and number of multiple cameras are configured by the camera's brightness imaging model.2)To solve the geometric distortion of image,this paper presents a global parameter guided camera geometric distortion rectification method,which estimates the local geometric rectification parameters of the camera by a calibrating image and corrects the subsequent measured images.Firstly,the global parameters of the camera are initially estimated in coarse-grained,and the approximate position of the feature points in the distorted calibrating image.Secondly,using the method of finding centroid with threshold to calculate the exact position of feature points in the neighborhood of the estimated position.Finally,the local geometric rectification parameters of the camera are calculated in fine-grained.The experimental results show that the geometric distortion of the distorted image can be well rectified,and the rectification error can be controlled at the sub-pixel level.3)Aiming at the phenomenon of image brightness distortion,this paper analyses its causes.Aiming at the vignetting effect of the image,this paper proposes a polynomial-based image vignetting rectification method to perform vignetting rectification on the measured image.Aiming at image degradation,a Wiener filtering method based on camera point spread function is proposed to restore the measured image.Finally,a multi-camera image fusion method based on vignetting coefficient is proposed to fuse multiple rectified images.Contrast experiments show that the fused image has higher image quality after the image is rectified and merged.4)A multi-CCD camera measurement system with wide field of view is designed and implemented.A 55-inch LCD module is used as the measurement object.The actual performance and effect of the system are tested,and the performance evaluation table is given to illustrate the effectiveness of the proposed algorithm.