| The arc moving process of low voltage apparatus plays an important role for the disjunction ability of the contact, electrical life and its cause of invalidation. To improve its reliability, it is effective to investigate the dynamic change of the whole process from arcing to arc suppress.Edge detection is an important part of the digital image processing. Detecting the edge of the image of the electrical arc is the precondition for the research of the dynamic change of the arc. So it is especially necessary for this research to find an appropriate detection algorithm with a good detecting result. This subject choose arc image as the research object.This paper introduces various theories and methods relevant to this subject, such as image segmentation, edge detection, pattern recognition etc. And this paper also introduces some functions and methods often used in digital image processing.Some conventional detection operators are analysed in detail, such as Roberts operator, Sobel operator and Laplacian operator, and also apply this operators to the arc image to test their detection results. But these conventional detection operators have a common shortcoming: they are too simple. This made their performance of noise suppressing and edge orientation is not very good. We also analyse LoG operator in this way. Although it is more complicated, it also cannot get a satisfactory result.John Canny presented Canny criteria for edge detection, and also presented an algorithm based on these criteria, named Canny operator. In this paper, we analyse Canny criteria and Canny operator in detail.We compare and evaluate the algorithms mentioned above. Based on these algorithms, and consider the property of the arc image, we proposed a new multi-stage algorithm. The proposed algorithm involves the class separability criterion in pattern recognition, and double-threshold method and non-maximum suppression proposed in Canny operator. We apply this algorithm to the arc image, and get a better result.
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