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Proceedings Paper

Addressing challenges of modulation transfer function measurement with fisheye lens cameras
Author(s): Brian M. Deegan; Patrick E. Denny; Vladimir Zlokolica; Barry Dever; Laura Russell
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Paper Abstract

Modulation transfer function (MTF) is a well defined and accepted method of measuring image sharpness. The slanted edge test, as defined in ISO12233 is a standard method of calculating MTF, and is widely used for lens alignment and auto-focus algorithm verification. However, there are a number of challenges which should be considered when measuring MTF in cameras with fisheye lenses. Due to trade-offs related Petzval curvature, planarity of the optical plane is difficult to achieve in fisheye lenses. It is therefore critical to have the ability to accurately measure sharpness throughout the entire image, particularly for lens alignment. One challenge for fisheye lenses is that, because of the radial distortion, the slanted edges will have different angles, depending on the location within the image and on the distortion profile of the lens. Previous work in the literature indicates that MTF measurements are robust for angles between 2 and 10 degrees. Outside of this range, MTF measurements become unreliable. Also, the slanted edge itself will be curved by the lens distortion, causing further measurement problems. This study summarises the difficulties in the use of MTF for sharpness measurement in fisheye lens cameras, and proposes mitigations and alternative methods.

Paper Details

Date Published: 13 March 2015
PDF: 10 pages
Proc. SPIE 9403, Image Sensors and Imaging Systems 2015, 94030F (13 March 2015); doi: 10.1117/12.2083347
Show Author Affiliations
Brian M. Deegan, Valeo Vision Systems (Ireland)
Patrick E. Denny, Valeo Vision Systems (Ireland)
Vladimir Zlokolica, Valeo Vision Systems (Ireland)
Barry Dever, Valeo Vision Systems (Ireland)
Laura Russell, Valeo Vision Systems (Ireland)

Published in SPIE Proceedings Vol. 9403:
Image Sensors and Imaging Systems 2015
Ralf Widenhorn; Antoine Dupret, Editor(s)

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