Reduced energy-ratio measure for robust autofocusing in digital camera

Sang Yong Lee, Jae Tack Yoo, Yogendera Kumar, Soo Won Kim

Research output: Contribution to journalArticlepeer-review

64 Citations (Scopus)


A robust and power efficient focus measure applicable in digital cameras is proposed. This measure, namely reduced energy-ratio (RER), uses the dc component and the lowest order five AC components of the discrete cosine transform (DCT) and is expressed as the ratio of the AC and DC components. The low-frequency AC and DC components contain the most energy (information) of an image as well as the detailed edge and base edge information. Autofocus score calculation method is used to assess the performance of the proposed measure and to compare it with other measures. Experimental results under various conditions verify the robustness of the proposed focus measure for the Gaussian as well as impulsive noises.

Original languageEnglish
Pages (from-to)133-136
Number of pages4
JournalIEEE Signal Processing Letters
Issue number2
Publication statusPublished - 2009


  • Autofocus
  • Digital camera
  • Discrete cosine transform (DCT)
  • Focus measure

ASJC Scopus subject areas

  • Signal Processing
  • Electrical and Electronic Engineering
  • Applied Mathematics


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