At present

pixel level edge detection algorithm is often used in visual measurement of parts size

which cannot meet the high precision measurement requirements. To improve the precision of part size measurement

a subpixel level part size measurement method with the help of the improved Canny operator was proposed. Firstly

adaptive median-Gaussian filtering is used to filter the image of parts

which can effectively remove noise while preserving more edge information. Then the gradient of the image is calculated and the edge points are found by using the quadratic interpolation. Secondly

the link algorithm is used to link the edge points and perform double threshold processing to extract the image subpixel edge contour. Finally

the minimum external rectangle of the contour is obtained and the part size is obtained. Experimental results show that the present method can effectively solve the accurate positioning of the contour of parts

and the measurement error is below 1 pixel. It has high stability while ensuring the measurement accuracy and efficiency.