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Sensors 2011, 11(9), 8281-8294; doi:10.3390/s110908281

Robust Automatic Focus Algorithm for Low Contrast Images Using a New Contrast Measure

2,* , 2
1 Department of Computer Science and Engineering, Shanghai Jiao Tong University, NO. 800 Dongchuan Road, Shanghai 200240, China 2 School of Computer Science and Technology, Wuhan University of Science and Technology, NO. 947 Heping Road, Wuhan 430081, Hubei, China
* Author to whom correspondence should be addressed.
Received: 1 August 2011 / Revised: 23 August 2011 / Accepted: 24 August 2011 / Published: 25 August 2011
(This article belongs to the Section Physical Sensors)
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Low contrast images, suffering from a lack of sharpness, are easily influenced by noise. As a result, many local false peaks may be generated in contrast measurements, making it difficult for the camera’s passive auto-focus system to perform its function of locating the focused peak. In this paper, a new passive auto-focus algorithm is proposed to address this problem. First, a noise reduction preprocessing is introduced to make our algorithm robust to both additive noise and multiplicative noise. Then, a new contrast measure is presented to bring in local false peaks, ensuring the presence of a well defined focused peak. In order to gauge the performance of our algorithm, a modified peak search algorithm is used in the experiments. The experimental results from an actual digital camera validate the effectiveness of our proposed algorithm.
Keywords: auto-focus; low contrast; contrast measure; noise reduction auto-focus; low contrast; contrast measure; noise reduction
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Xu, X.; Wang, Y.; Tang, J.; Zhang, X.; Liu, X. Robust Automatic Focus Algorithm for Low Contrast Images Using a New Contrast Measure. Sensors 2011, 11, 8281-8294.

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