Depth of field estimation: Theory, experiment, and application

Rania H. Abd El-Maksoud, Lirong Wang, José M. Sasian, Valorie S. Valencia

Research output: Chapter in Book/Report/Conference proceedingConference contribution

2 Scopus citations


When a fingerprint image is acquired via contactless means, the depth of field must be measured. Due to the natural curvature of a finger, not all of the fingerprint will be in focus. Defocus introduced by such curvature may cause contrast reduction, loss of certain spatial frequencies, blurriness, and contrast reduction and reversal. We need to ensure that the imaging system has enough depth of field to compensate for the longitudinal displacement created by the finger curvature. This paper presents theoretical and experimental techniques to simulate and measure the depth of field of an imaging system. Experimentally, image contrast as a function of object position along the optical axis is measured for several spatial frequencies of interest, and the defocused modulation transfer function (MTF) is determined. The acceptable contrast range is defined by the system application and used to determine the corresponding depth of field. A diffraction image irradiance theoretical model is developed, and the Zemax optical design program is used to simulate depth of field. The experimental and simulated depth-of-field results are presented and applied to a contactless fingerprint sensor.

Original languageEnglish (US)
Title of host publicationNovel Optical Systems Design and Optimization XII
StatePublished - 2009
EventNovel Optical Systems Design and Optimization XII - San Diego, CA, United States
Duration: Aug 3 2009Aug 4 2009

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X


OtherNovel Optical Systems Design and Optimization XII
Country/TerritoryUnited States
CitySan Diego, CA


  • Depth of field
  • contactless
  • contrast
  • defocus
  • diffraction point spread function
  • fingerprint sensor
  • modulation transfer function
  • resolution

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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