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- This paper presents a novel autofocus algorithm in which the type of target object is fixed and the range of working distance is known a priori. The key idea of the algorithm is to compare the blurry value computed from the input image to the ones pre-recorded in the learning step. The blurry value is derived from the Point Spread Function (PSF) estimated from the input image. The information on working distance associated to the reference blurry value is used to adjust the lens position to the focus position. This algorithm requires at most three shots (initial shot and two steps of lens position adjustment) to reach the focus position. From our experiment, the accuracy of our autofocus algorithm is about 93%. The algorithm can be applied for the autofocus module of an industrial visual inspection, especially in the area of high magnification applications.
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