Study On Sub-pixel Edge Location Based On Digital Image

With the development of modern industry and the improvement of the products machining precision,the higher requirements to the measurement technology are needed.Non-contacting measurement technology to the geometric parameters of objects becomes a key point of research by using image processing technology.This measurement technology regards the images of the measurand as methods or carriers of detection and transport.The measuring probe actually is a CCD camera.Then extract the useful information by processing the images of the object collected by the computer,CCD camera and the image collecting card and finally the expected geometric parameters are obtained.However,the accuracy of the measuring results is most cared in geometric parameter measurements.In this paper , the main factors of affecting the accuracy of image measurement have been analyzed according to the composition of the image measurement system and the principle of the image processing,and it has been found that the accuracy of edge location is the direct one.Therefore,the sub-pixel edge location technology has been further studied based on the digital image in this paper.This paper consists of six parts and the contents are showed as follows:Ⅰ.IntroductionThis part has introduced the research contents and the application fields of digital image processing technology,and also introduced the current development and the tendency of the image measurement technology.On this basis,the contents of our research have been proposed.Ⅱ.Factors of affecting the accuracy of image measurementThis part has analyzed the factors of affecting the accuracy of image measurement qualitatively and given some methods of how to eliminate or decrease them according to the composition of the image measurement system and digital image processing technology.This provides us the theoretical supports to improving the measurement accuracy.Ⅲ. Image Smoothing and edge detectionAt first,this part has studied the working principles of the image smoothing algorithms and the edge detecting operators,and then the properties of these operators have been compared by experiments.Finally,from the experiment results,the conclusion that both Median filtering operator and Sobel operator are the best in their filed has been obtained.Ⅳ.Sub-pixel edge location algorithms and evaluationFirstly,this part has given a compendious explanation of all kinds of sub-pixel edge location algorithms,and mainly introduced the Gray moment operator,Gaussian fitting operator and Polynomial interpolation operator.Then,according to the camera imaging principle,the performance of this three kinds of algorithms has been compared quantitatively and qualitatively respectively by computer simulations and realistic experiments.Finally,the conclusion that Gaussian fitting operator is the best one has been obtained.Ⅴ.The effect of camera lens distortion on sub-pixel edge locationAt first,the models of camera imaging and lens non-linear distortion have been studied,and the radial distortion coefficients have been solved by the experimental method.Then,the radial distortion coefficients have been introduced to the sub-pixel edge location operators to correct the positional errors of edges.Ⅵ. ConclusionThe conclusion and the deficiency of this paper have been given,and the key point of further research has been proposed too.