At present,the detection of piston rings is general manual detection.The vision technology is used to extract the contour of the closed gap of the piston ring and the image contour is processed to get the measurement result.Compared with manual detection,the detection speed is faster and the accuracy is higher.The traditional edge detection process mostly uses the Canny edge detector,Gaussian filtering method is used to filter the image.In the process of piston ring contour processing,higher requirements are put for contour extraction accuracy.As a low-pass filtering algorithm,Gaussian filtering has no protective effect on the contour,which will cause the contour edge image to be blurred.Aiming at this problem,an improved Canny edge detector was proposed,which combined median filtering and Fourier transform to effectively improve the extraction accuracy of edge contour.