Abstract: The research on recognition of bridges is of a very important significance in military and civil. The relevant studies at home and abroad have obtained certain effects, but have also some weak points: the application range is not wide, the processing speed is not so fast and so on. Based on the characteristics of infrared image, this paper puts forward a method that uses iteration to calculate and split threshold to get the binary images. Then the target points are extracted by morphology method. Based on bridge’s linear property, the straight lines are extracted and connected from the target points by Radon transform. This algorithm is universal for bridge recognition of infrared image in water area, and it’s simple, intuitive with a high calculating speed.

Key words: infrared image, bridge target, morphology, extracting the straight line