Multimedia Tools and Applications

, Volume 69, Issue 1, pp 139–156 | Cite as

A comparison of contrast measurements in passive autofocus systems for low contrast images

  • Xin Xu
  • Yinglin Wang
  • Xiaolong Zhang
  • Shunxin Li
  • Xiaoming Liu
  • Xiaofeng Wang
  • Jinshan Tang
Article

Abstract

A number of contrast measurements have been investigated and compared in the literature. Each of them exhibits an ideal curve with a well defined peak standing for the best focused image. However, a focused image obtained in low light conditions possesses a small contrast value, which may be easily influenced by noise. In this case, contrast measurements may generate fluctuant curves with many local peaks. This paper presents a comparison among six contrast measurements in passive autofocus systems towards a non-previously researched object of low contrast images. The criterium to evaluate the performance of each measurement is unimodality. And we assess the similarity of the resulting curves with an ideal focus curve which exhibits a single peak and an absence of plateau. Experimental results from six typical image sequences indicate that Tenengrad and CMAN approaches yield the best performance, but it is still necessary to derive a more elaborated method because both methods fail to generate a single sharp peak in some circumstances.

Keywords

Autofocus Low contrast image Contrast measurement 

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Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  • Xin Xu
    • 1
  • Yinglin Wang
    • 2
  • Xiaolong Zhang
    • 1
  • Shunxin Li
    • 1
  • Xiaoming Liu
    • 1
  • Xiaofeng Wang
    • 1
  • Jinshan Tang
    • 1
  1. 1.School of Computer Science and TechnologyWuhan University of Science and TechnologyWuhanChina
  2. 2.Department of Computer Science and EngineeringShanghai Jiao Tong UniversityShanghaiChina

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