Abstract
The working range of triangulation-based measuring systems is often limited by the depth of field of the applied optical system. Approaches such as increasing the depth of field range by reducing the aperture are limited in their effectiveness by a lower light yield and thus require a longer exposure time. Focus adjustable optics enable the depth of field to be modified and thus effect the location and shape of the working range. However, the validity of the model-based camera calibration is limited to the corresponding focus setting, especially with optics that exhibit the effect of focus breathing, i. e. whose focal length change with the focus setting. This paper presents an approach to model the calibration parameters over the entire focus range of a lens using function fitting of the camera parameters and the influence of different configurations on this process is examined.
Zusammenfassung
Der Arbeitsbereich triangulationsbasierter Messsysteme wird häufig durch die Tiefenschärfe des verwendeten optischen Systems begrenzt. Ansätze, wie die Vergrößerung des Tiefenschärfebereichs durch Verkleinerung der Blende sind in ihrer Wirksamkeit durch eine geringere Lichtausbeute begrenzt und erfordern daher eine längere Belichtungszeit. Mit fokussierbaren Optiken lässt sich die Schärfentiefe verändern und damit die Lage und Form des Arbeitsbereichs beeinflussen. Allerdings ist die Gültigkeit der modellbasierten Kamerakalibrierung auf die jeweilige Fokuseinstellung beschränkt, insbesondere bei Optiken, die den Effekt des Focus Breathings aufweisen, d. h. deren Brennweite sich mit der Fokuseinstellung ändert. In diesem Beitrag wird ein Ansatz zur Modellierung der Kalibrierungsparameter über den gesamten Fokusbereich eines Objektivs mittels Funktionsanpassung der Kameraparameter vorgestellt und abschließend wird der Einfluss verschiedener Konfigurationen auf diesen Prozess untersucht.
About the authors
Hagen Bossemeyer works as a research associate at the Institute of Measurement and Automatic Control at the Leibniz University Hannover, where he also received his master’s degree in 2018. His research is focussed on laser triangulation sensors for large measurement ranges leading to the development of an adaptive measuring system.
Patrick Ahlborn received his master’s degree in Mechanical Engineering from the Leibniz University Hannover in 2020. He gained experiences about optical 3D-measurement systems and camera calibration methods during his studies and master thesis at the IMR. Since 2020 he works as a research associate at the IFW focussing on multi-axis direct drives for machine tools.
Markus Kästner has been head of the production metrology group of the Institute of Measurement and Automatic Control at Leibniz University of Hannover since 2008. The research activities of the research group include the research and development of methods for optical 3D measurement as well as for characterising the shape of industrially manufactured components in different geometric scale ranges.
Eduard Reithmeier has been director of the Institute of Measurement and Automatic Control at the Leibniz University Hannover since 1996. The research activities are concentrated in the three research groups of control engineering, production metrology, as well as industrial and medical imaging.
References
1. A. Miks, J. Novak and P. Novak, “Analysis of imaging for laser triangulation sensors under Scheimpflug rule,” Optics express, vol. 21, Nr. 15, p. 18225–18235, 2013.10.1364/OE.21.018225Search in Google Scholar
2. J. Krames, “Umbildung und Entzerrung photographischer Aufnahmen nach Theodor Scheimpflug,” Festschrift zum 150 Jährigen Bestand des staatlichen Vermessungswesens in Österreich, 1956.Search in Google Scholar
3. K. Tanaka, “Zoom lens without focus-breathing phenomena,” SPIE, 2001, p. 63–67.Search in Google Scholar
4. L. Hinz, M. Kästner and E. Reithmeier, “Adaptive camera calibration for a focus adjustable liquid lens in fiber optic endoscopy,” SPIE Optics + Optoelectronics, 2021, p. 37.10.1117/12.2592653Search in Google Scholar
5. Y.-S. Chen, S.-W. Shih, Y.-P. Hung and C.-S. Fuh, “Simple and efficient method of calibrating a motorized zoom lens,” Image and Vision Computing, vol. 19, Nr. 14, p. 1099–1110, 2001.10.1016/S0262-8856(01)00069-5Search in Google Scholar
6. R. G. Willson, “Modeling and calibration of automated zoom lenses,” SPIE, 1994, p. 170–186.Search in Google Scholar
7. B. Wu, H. Hu, Q. Zhu and Y. Zhang, “A Flexible Method for Zoom Lens Calibration and Modeling Using a Planar Checkerboard,” Photogrammetric Engineering & Remote Sensing, vol. 79, Nr. 6, p. 555–571, 2013.10.14358/PERS.79.6.555Search in Google Scholar
8. M. Li and J.-M. Lavest, “Some aspects of zoom lens camera calibration,” IEEE Transactions on Pattern Analysis and Machine Intelligence, vol. 18, Nr. 11, p. 1105–1110, 1996.10.1109/34.544080Search in Google Scholar
9. D. C. Brown, “Close-Range Camera Calibration,” Photogrammetric Engineering, vol. 37, p. 855–866, 1971.Search in Google Scholar
10. A. E. Conrady, “Decentred Lens-Systems,” Monthly Notices of the Royal Astronomical Society, vol. 79, Nr. 5, p. 384–390, 1919.10.1093/mnras/79.5.384Search in Google Scholar
11. Z. Zhang, “A flexible new technique for camera calibration,” IEEE transactions on pattern analysis and machine intelligence, vol. 22, Nr. 11, p. 1330–1334, 2000.10.1109/34.888718Search in Google Scholar
12. R. Tsai, “A versatile camera calibration technique for high-accuracy 3D machine vision metrology using off-the-shelf TV cameras and lenses,” IEEE Journal on Robotics and Automation, vol. 3, Nr. 4, p. 323–344, 1987.10.1109/JRA.1987.1087109Search in Google Scholar
13. J. Heikkila and O. Silven, “A four-step camera calibration procedure with implicit image correction,” Proceedings of IEEE Computer Society Conference on Computer Vision and Pattern Recognition, 1997, p. 1106–1112.10.1109/CVPR.1997.609468Search in Google Scholar
14. K. H. Strobl and G. Hirzinger, “More accurate pinhole camera calibration with imperfect planar target,” 2011 IEEE International Conference on Computer Vision Workshops (ICCV Workshops), IEEE, 2011, p. 1068–1075.10.1109/ICCVW.2011.6130369Search in Google Scholar
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