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Telephoto and Zoom Lens Calibration

Telephoto and Zoom Lens Calibration. Vitaliy Orekhov Imaging, Robotics, & Intelligent Systems Laboratory The University of Tennessee December 1, 2006. Outline. IRIS Demos Tasks Telephoto Lens Calibration Lens Parameter Optimization in C++ Thesis/Publication

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Telephoto and Zoom Lens Calibration

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  1. Telephoto and Zoom Lens Calibration Vitaliy Orekhov Imaging, Robotics, & Intelligent Systems Laboratory The University of Tennessee December 1, 2006

  2. Outline • IRIS Demos • Tasks • Telephoto Lens Calibration • Lens Parameter Optimization in C++ • Thesis/Publication • Telephoto and Zoom Lens Calibration Results • Previous Observations • 50mm Lens • 18-70mm Lens • 70-210mm Lens • Overview of Literature on Zoom Lens Calibration • Conclusions and Future Work

  3. IRIS Demos • Homecoming Demo • URPR Demo for DOE • Engineer’s Day Demo URPR Demo Engineer’s Day Demo

  4. IRIS Tasks • Telephoto Lens Calibration • Lens Parameter Optimization in C++ • Thesis/Publication • Telephoto and zoom lens calibration • Capture images with Rodenstock 50mm lens • Put together a portable image recording setup

  5. Rodenstock 50mm Lens Sony DXC-930 CCD Color Video Camera Sony ExwareHAD SSC-DC393 CCD Color Video Camera IQEye3 Camera CCD Video Camera Module

  6. Rodenstock 50mm Lens 1/3 Type Sensor CCD Board

  7. IRIS Tasks • Telephoto Lens Calibration • Lens Parameter Optimization in C++ • Thesis/Publication • Final Step of Complete Camera Calibration • Levenberg-Marquardt nonlinear least squares algorithm • Numerical Recipes Implementation • Code is completely written • Still need to finish debugging and run test to compare performance to MATLAB

  8. IRIS Tasks • Telephoto Lens Calibration • Lens Parameter Optimization in C++ • Thesis/Publication • Introduction • Survey and Background Theory • Camera Models and Calibration • Wide Angle and Omnidirectinal Camera Calibration • Telephoto and Zoom Lens Calibration • Complete Camera Calibration • Experimental Results and Comparison • Automatic Model Complexity Selection Validation • Telephoto and Zoom Lens Calibration Synthetic Data Real Data • Improved Complete Camera Calibration Method • Practical Implementations • Real Time Video Distortion Correction • Calibration GUI • Summary and Conclusion

  9. Outline • IRIS Demos • Tasks • Telephoto Lens Calibration • Lens Parameter Optimization in C++ • Thesis/Publication • Telephoto and Zoom Lens Calibration Results • Previous Observations • 50mm Lens • 18-70mm Lens • 70-210mm Lens • Overview of Literature on Zoom Lens Calibration • Conclusions and Future Work

  10. Telephoto and Zoom Lens Calibration Results • Motivation: Normal to Telephoto Lens Calibration • Previous results were inconclusive • Go back to the basics (50mm Lens) (1-28mm, 2-100mm, 3-200mm, 4-300mm)

  11. Nikon 50mm Lens • Lens Specifications • Nikon Nikkor AF/MF 50mm F/1:1.4-16 • Manual aperture f2.8 • Varied focus settings www.nikon.com (focus settings: 1-0.7m, 2-1.0m, 3-1.2m, 4-1.5m, 5-2.1m, 6-3.0m, x-image center)

  12. Nikon18-70mm Lens • Lens Specifications • Nikon Nikkor AF-S 18-70mm 1:3.5-4.5 • Manual aperture • Fixed focus settings • Varied focal length www.nikon.com Focal Length Estimation with IRIS Method (1-18mm, 2-50mm, 3-70mm, x-image center)

  13. Nikon18-70mm Lens • Lens Specifications • Nikon Nikkor AF-S 18-70mm 1:3.5-4.5 • Manual aperture • Fixed focus settings • Varied focal length www.nikon.com Focal Length Estimation with OpenCV (1-18mm, 2-50mm, 3-70mm, x-image center)

  14. Nikon 70-210mm Lens • Lens Specifications • Nikon Nikkor AF/MF 70-210mm F/4-5.6 • Focal length 70-210mm • Lens construction: 12 elements in 9 groups • Manual aperture • Varied focus settings (1.5m, 2m, 3m) • Varied focal length (70mm, 90mm, 110mm, 135mm, 210mm) www.amazon.com

  15. Varifocal Error Measurements

  16. Focal Length Measurements

  17. Principal Point Location

  18. f=210mm (3m) f=70mm (1.5m) Nikon 70-210mm Lens Principal Point Location

  19. Nikon 70-210mm Lens Principal Point Location

  20. Distortion Center [Hartley05] R. I. Hartley and S. B. Kang, “Parameter-free Radial Distortion Correction with Centre of Distortion Estimation,” Computer Vision, 2005. ICCV 2005. Tenth IEEE International Conference on , vol.2, no.pp. 1834- 1841, 17-20 Oct. 2005 • Center of distortion is found by computing the fundamental matrix relating the known coordinates of points on a planer calibration pattern and the extracted points from the image. • Radial distortion forces ideal points to be expanded towards or away from the center of distortion. Epipole in one view is the camera center of the other view. Center of radial expansion is the epipole.

  21. Distortion Center

  22. f=210mm at 3 meters from target Distortion Center

  23. Survey of Zoom Lens Calibration Methods Willson, R.G., Modeling and Calibration of Automated Zoom Lenses, Ph.D. Thesis, Carnegie Mellon University, CMU-RI-TR-94-03, 1994 Mengxiang Li; Lavest, J.-M., "Some aspects of zoom lens camera calibration," Pattern Analysis and Machine Intelligence, IEEE Transactions on , vol.18, no.11pp.1105-1110, Nov 1996 Collins, R.T.; Tsin, Y., "Calibration of an outdoor active camera system," Computer Vision and Pattern Recognition, 1999. IEEE Computer Society Conference on. , vol.1, no.pp.-534 Vol. 1, 1999 Yong-Sheng Chen; Shen-Wen Shih; Yi-Ping Hung; Chiou-Shann Fuh, "Camera calibration with a motorized zoom lens," Pattern Recognition, 2000. Proceedings. 15th International Conference on , vol.4, no.pp.495-498 vol.4, 2000 Ahmed, M.T.; Farag, A.A., "A neural optimization framework for zoom lens camera calibration ," Computer Vision and Pattern Recognition, 2000. Proceedings. IEEE Conference on , vol.1, no.pp.403-409 vol.1, 2000 Thirthala, S.R.; Sinha, S.N.; Pollefeys, M., "Calibration of pan-tilt-zoom (PTZ) cameras and omni-directional cameras," Computer Vision and Pattern Recognition, 2005. CVPR 2005. IEEE Computer Society Conference on , vol.2, no.pp. 1198 vol. 2-, 20-25 June 2005

  24. Mengxiang Li; Lavest, J.-M., "Some aspects of zoom lens camera calibration," Pattern Analysis and Machine Intelligence, IEEE Transactions on , vol.18, no.11pp.1105-1110, Nov 1996 Parameters are calibrated at discrete lens positions (focus and zoom) based on Tsai Camera Calibration method • Determine principal point by zooming • Center of expansion moves about 0.5 of a pixel on average • Fixed principal point • Focal length changed as a smooth function • Focus effect is not so important for short distances but increases greatly for long distances • Polynomials of order five were used to model the surface www.cas.kth.se/~hic/active-vision.pdf KTH Head-Eye System Focus: 0.8m – inf. Lens: f=12.5mm to 75mm Residual errors, i.e., fitness between model and data for different zoom and focus settings. Least squares technique is applied to minimize measurement error in images. Calibrated results of focal length (fx) for the zoom lens mounted on the KTH head-eye system.

  25. SONY / EVI370 www.broadcaststore.com Figure 2. Calibration by zooming. Left: image center vs. zoom. Right: Detail of image center for one camera. Image center (384,247). Collins, R.T.; Tsin, Y., "Calibration of an outdoor active camera system," Computer Vision and Pattern Recognition, 1999. IEEE Computer Society Conference on. , vol.1, no.pp.-534 Vol. 1, 1999 Parameters are calibrated at discrete lens positions using Tsai Camera Model • First the center of zoom expansion is recovered • 205 images for each camera • Image center can vary by as much as 40 pixels • Later calibration by pure rotation determines the remaining intrinsic parameters (f, s, k) • Extrinsic calibration (R) is performed last Color Camera- 1/3 inch NTSC HAD 12x optical zoom, auto focus, auto iris lens High resolution: 768 x 494 effective pixels, 460 TV lines Lens: f=5.4mm to 64.8mm, F1.8 to 2.7

  26. Ahmed, M.T.; Farag, A.A., "A neural optimization framework for zoom lens camera calibration ," Computer Vision and Pattern Recognition, 2000. Proceedings. IEEE Conference on , vol.1, no.pp.403-409 vol.1, 2000 • Since optimal polynomial fails to follow complex variations in the model parameters they use neural network approach • Parameters are calibrated at discrete lens positions based on Tsai Camera Calibration method except they decouple distortion parameter estimation • Use chessboard calibration pattern • Focal length range from 11mm to 110mm (10x) Focal Length Yong-Sheng Chen; Shen-Wen Shih; Yi-Ping Hung; Chiou-Shann Fuh, "Camera calibration with a motorized zoom lens," Pattern Recognition, 2000. Proceedings. 15th International Conference on , vol.4, no.pp.495-498 vol.4, 2000 • Parameters are calibrated at discrete lens positions based on Weng (92) Camera Calibration method • Use calibration pattern with circular control points • Different calibration patterns are used depending on the field of view of a particular lens setting • Fujinon 12.5-75 mm manual lens • Focus range from 1m to ∞ • 3 servo motors used to control lens settings

  27. Future Work • Telephoto and Zoom Lens Calibration • Perform experiments on 70-300mm lens • Calculate the center of zoom expansion • Lens Parameter Optimization in C++ • Debug and compare optimization results of parameters • Continue work on user friendly calibration GUI • Thesis/Publication • Finish adding content of telephoto and zoom lens calibration

  28. Thank you Suggestions/Comments/Questions

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