1 / 32

Telephoto Lens Calibration and Model Complexity Selection

Telephoto Lens Calibration and Model Complexity Selection. Vitaliy Orekhov Imaging, Robotics, & Intelligent Systems Laboratory The University of Tennessee August 11, 2006. Outline. Telephoto Lens Calibration Definition of Telephoto Lens Tamron 28-300mm Lens Calibration Results

christiansenj
Download Presentation

Telephoto Lens Calibration and Model Complexity Selection

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Telephoto Lens Calibration and Model Complexity Selection Vitaliy Orekhov Imaging, Robotics, & Intelligent Systems Laboratory The University of Tennessee August 11, 2006

  2. Outline • Telephoto Lens Calibration • Definition of Telephoto Lens • Tamron 28-300mm Lens Calibration Results • Nikkor 18-70mm Calibration Results • Model Complexity Selection • Background and Theory • Short Survey • Experiment Results • Calibration GUI

  3. Telephoto Lens • Telephoto lens is one where the ratio of EFL:BFD is greater than unity and at least a value of 2.0 [1] • Telephoto lens is a lens whose focal length is significantly longer than the focal length of a normal lens (ex. For a 35mm camera, a normal lens generally has a focal length of 50mm while 70mm or more is considered telephoto)[2] • Classification of telephoto lenses [3] • Short telephoto (70-120mm) • Medium telephoto (135-210mm) • Extreme telephoto lenses (300mm or more) [1] Booth, L. “The Telephoto Lens.” Proc. Opt. Conv. 861, 1936 [2] www.wikipedia.com [3] www.photography.about.com/od/basics/a/bptelephoto.htm Nikon 200-400mm Source: www.dpreview.com

  4. Lens Specifications • Tamron SP AF 28-300mm • Ashperical Lens Elements • 13 groups and 15 elements • Angle of view 75-8 deg. • Focal length 28-300 mm (11X) • Distortion • Some barrel distortion at 28mm • Very slight pin-cushion distortion at 300mm • Good performance for a wider range zoom lens • http://www.photo.net/equipment/tamron/28_300_Di/page3.html 300mm/5m

  5. Source: Thomas Hogan’s Complete Guide to the Nikon D70 Nikon D70 CCD Specifications • Modified version of the Sony ICX413AQ • Size: 0.93x0.61” (23.7x15.6mm) • Pixel size: 7.8 microns • 8 to 10 images captured at each focal length setting • 28mm, 100mm, 200mm, and 300mm • At each focal length the focus was adjusted to best capture the entire calibration pattern.

  6. Model Complexity Selection 28 mm 100 mm 200 mm 300 mm

  7. Tamron 28mm Original Image Corrected Image4 Radial 2 Tangential

  8. Tamron 100mm Corrected Image2 Radial 3 Tangential Original Image

  9. Tamron 200mm Original Image Corrected Image2 Radial 0 Tangential

  10. Tamron 300mm Original Image Corrected Image2 Radial 0 Tangential

  11. Importance of Correct Distortion Model Original Image Overcorrected Image

  12. Calibration Error Calibration Error for Tamron 28-300 mm Lens • Reprojection error of calibration points is relatively small and less than the error obtained with wide angle and fisheye lenses. • Pixel errors in both x an y direction are better than using OpenCV method Calibration Error for Other Lenses

  13. Calibration Results • Principal point estimation Expect some principal point shift due to misalignment of the optical components found in the lens. The position and orientation of the lens components are changed by adjusting the focus and zoom. (1-28mm, 2-100mm, 3-200mm, 4-300mm)

  14. Calibration Results • Principal point estimation using OpenCV calibration method (1-28mm, 2-100mm, 3-200mm, 4-300mm)

  15. Calibration Results • Center of distortion estimation with Hartley/Kang method using epipolar geometry constraints (1-28mm, 2-100mm, 3-200mm, 4-300mm)

  16. Focal Length Estimation Results Using IRIS Implementation Results Using OpenCV * Focal length % error is reported only for reference. Focal length measured by the camera calibration may be different from focal length specified by the manufacturer.

  17. Results with Varied Focus Tamron Lens at 200mm (focus setting: 1-2.5m, 2-4m, 3-5m)

  18. Results with Varied Focus Tamron Lens at 200mm (focus setting: 1-2.5m, 2-4m, 3-5m)

  19. Results with Varied Focus Tamron Lens at 200mm (focus setting: 1-2.5m, 2-4m, 3-5m)

  20. Lens/CCD Specifications • Lens Specifications • Nikon Nikkor AF-S 18-70mm 1:3.5-4.5 • Focal length 18-70 mm (4X) • Angle of view: 76 ~ 22 degrees • Lens construction: 15 elements in 13 groups

  21. Initial Calibration Results • Principal point estimation with IRIS implementation (1-18mm, 2-50mm, 3-70mm, x-image center)

  22. Initial Calibration Results • Principal point estimation using OpenCV calibration method (1-18mm, 2-50mm, 3-70mm, x-image center)

  23. Focal Length Estimation Results Using IRIS Implementation Results Using OpenCV * Focal length % error is reported only for reference. Focal length measured by the camera calibration may be different from focal length specified by the manufacturer.

  24. Zoom Lens Calibration • If only the reprojection error is considered then the performance of the calibration method is good • If actual extraction of camera parameters is included, the estimated parameters are more erroneous at larger focal length settings • The focal length setting at which calibration fails is difficult to determine due to coupling of lens settings

  25. Distortion Model Complexity Selection • Necessary for a complete and automatic camera calibration method • Answers the question, “How many parameters should be used to model radial and tangential distortion for a particular imaging system?” Are two radial coefficients and two tangential coefficients sufficient to model the lens distortion? Should tangential distortion be ignored while increasing the number of coefficient used to model radial distortion?

  26. Distortion Model Complexity Selection • In most cases the distortion model is selected manually depending on which model provides better results for a particular system. • Normal lenses can be modeled with lower order polynomial terms while higher order terms may be necessary for wide-angle and fish-eye lenses [Shah96] • It was shown in [Kannala04] that lower RMS residual error can be obtained with more complex distortion models. 2 radial coefficients 4 radial coefficients [Kannala04] J. Kannala and S. Brandt, “A Generic Camera Calibration Method for Fish-eye Lenses,” In Proceeding of the IEEE International Conference on Pattern Recognition, , 2004, pp. 10-13 [Shah96] S. Shah, J. K. Aggarwal, “Intrinsic Parameter Calibration Procedure for a (High-Distortion) Fish-Eye Lens Camera with Distortion Model and Accuracy Estimation,” Pattern Recognition 29, No. 11, Novermber 1995, pp. 1175-1788.

  27. Name Formula AIC MDL BIC SSD CAIC Distortion Model Complexity Selection • A quantitative measure to aid in the selection of a model with reduced number of distortion coefficients without sacrificing accuracy • Compromise between how well model fits the data and the complexity of the model • Perform statistical model selection using Information Theoretic Criterion (AIC) Model selection criterions

  28. Other Model Selection Methods • Very few methods mention automatic model selection • [1] and [2] explore distortion model selection from Information Theoretic Criterion • Both papers validate the model selection by picking between three predetermined competing models (ex. without distortion, just with radial distortion, with both radial and tangential distortion) • [2] shows results of model selection with varied amounts of noise added to synthetic data • The same authors from [2] in [3] mention that future work will include model complexity selection • No results are shown on real data [1] G. Wei, K. Arbter, G. Hirzinger, “Active self-calibration of robotic eyes and hand-eye relationships with model identification,” IEEE Transaction Robotics and Automation, vol. 14(1), pp. 158-166, Feb. 1998. [2] M. T. El-Melegy and A. A. Farag, “Nonmetric lens distortion calibration: closed-form solutions, robust estimation and model selection,” in Ninth IEEE Int. Conf. on Computer Vision, 2003. vol. 1, pp. 554-559, 13-16 Oct. 2003. [3] M, Ahmed and A. Farag, “Nonmetric Calibration of Camera Lens Distortion: Differential Methods and Robust Estimation,” in IEEE Transactions on Image Processing, vol. 14, Iss. 8, pp. 1215-1230, August 2005.

  29. Results with Synthetic Data • Generated 8 800x600 images with random rotations and translations. • Radial and tangential distortion was added with both odd powered lens projection model and even powered radial distortion model • Radial distortion range • No distortion to 5 distortion coefficients • Tangential distortion • No distortion or 2 distortion coefficients

  30. Results with Synthetic Data • Noise was added to test the robustness of the method • Gaussian distribution with zero mean and standard deviation ranging from zero to 1.2 pixels in 0.2 increments • Model complexity selection was performed 50 times at each noise level • Each time a new set of synthetic data was generated with randomly selected distortion model (LPDD) and random translation and orientation was added • Model selection was performed between 6 competing models (most complex with 3 radial and 2 tangential coefficients) • Most of the error was in selecting whether to use tangential distortion

  31. Calibration GUI in C++

  32. Thank you Suggestions/Comments/Questions

More Related