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Proceedings Paper

Depth of field estimation: theory, experiment, and application
Author(s): Rania H. Abd El-Maksoud; Lirong Wang; José M. Sasian; Valorie S. Valencia
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Paper Abstract

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.

Paper Details

Date Published: 21 August 2009
PDF: 12 pages
Proc. SPIE 7429, Novel Optical Systems Design and Optimization XII, 74290W (21 August 2009); doi: 10.1117/12.829593
Show Author Affiliations
Rania H. Abd El-Maksoud, College of Optical Sciences, The Univ. of Arizona (United States)
Lirong Wang, College of Optical Sciences, The Univ. of Arizona (United States)
José M. Sasian, College of Optical Sciences, The Univ. of Arizona (United States)
Valorie S. Valencia, College of Optical Sciences, The Univ. of Arizona (United States)
Authenti-Corp (United States)


Published in SPIE Proceedings Vol. 7429:
Novel Optical Systems Design and Optimization XII
R. John Koshel; G. Groot Gregory, Editor(s)

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