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

Department of Computer Science and Engineering, Shanghai Jiao Tong University, NO. 800 Dongchuan Road, Shanghai 200240, China
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.
Sensors 2011, 11(9), 8281-8294;
Received: 1 August 2011 / Revised: 23 August 2011 / Accepted: 24 August 2011 / Published: 25 August 2011
(This article belongs to the Section Physical Sensors)
PDF [747 KB, uploaded 21 June 2014]


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. View Full-Text
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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MDPI and ACS Style

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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