The Study Of Defect Inspection Of Special Medium PCB By Computer Vision

Pattern recognition and Image Process are newly subjects rising with the development of modern computer technology,especially with the rapid development of computer hardware and pattern recognition theory in recent years,the applied subjects based on pattern recognition and image process gets further development,particularly in industrial production fields:such as the automatic inspection of product quality and the automatic control of the manufacture process.Printed circuit boards (PCB) defect inspection adopted image process has applied in practice. But for some special medium materials,such as liquid crystal display controller PCB,magnifiers must be used to gather images to gain enough precision of inspection for the weak contrast between the basic board and the conductor .The images near the light axes are much cleared than that far away from the light axes,so the images can not be simply segmented by black and white and inspected with the methods of PCB which are based on the black white image. In the condition,other way to inspect the defect of PCB must be found.Based on the analysis and conclusion of the existed methods of PCB defect inspection and widely gathered data,the author put forward a solution,in which two parameters-the distance of conductors and the width of conductor can be used to detect the defect of PCB. This method can detect most of the defects. First,we must filter the image to reduce noises,this process includes two phase:one is using the nearest neighbor middle filter(KNNMF) to reduce the isolated noises,the other is using gauss filter to remove white noises. Secondly we use Canny arithmetic operators to get the edge of image,and remove the short link of edge then link the edge with small clearance. At last we can calculate the distance of conductor and the width of conductor according to the grade direction to detect of defect of the circuit boards. In order to make the image process arithmetic to meet the demand of the real time .system,MMX technology is used to optimize the kernel arithmetic and increase the process greatly that make it possible to apply the microcomputer in the industry.This dissertation discusses the arithmetic of the image process,shows and explains the pseudocode,illustrates the feasibility and validity of liquid crystal display controller PCB defect inspection adopted image process.