Reciprocal Focus Profile

  • Authors:

  • Dong-Chen Tsai;Homer H. Chen

  • Affiliations:

  • Graduate Institute of Communication Engineering, National Taiwan University, Taipei, Taiwan;Graduate Institute of Communication Engineering, the Graduate Institute of Networking and Multimedia, and the Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan

  • Venue:
  • IEEE Transactions on Image Processing
  • Year:
  • 2012

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Abstract

A focus profile having a steeper peak is more resistant to image noise in the autofocus (AF) process of a digital camera. However, a focus profile of such shape normally has a flatter out-of-focus region on either side of the profile, resulting in a slow AF process due to the lack of clue about where the lens should move when the lens is in such regions. To address the problem, we provide a statistical analysis of the focus profile and show that a strictly monotonic transformation of the focus profile preserves the accuracy of the AF. On the basis of this analysis, we propose a new focus profile representation that transforms the focus profile to the reciprocal domain in which the reciprocal focus profile is modeled by a polynomial function. This transformation makes the AF mathematically tractable and boosts the search speed. Experimental results are shown to demonstrate the advantage of the proposed representation .