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Structured Light @

Structured Light @. Prasanna Rangarajan Dr. Marc P Christensen Vikrant R Bhakta Dr. Panos Papamichalis. Organization. Imaging under “Structured Light” what is “Structured Light” ? estimating depth using “Structured Light”

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Structured Light @

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  1. Structured Light @ Prasanna Rangarajan Dr. Marc P Christensen Vikrant R Bhakta Dr. Panos Papamichalis

  2. Organization Imaging under “Structured Light” • what is “Structured Light” ? • estimating depth using “Structured Light” • Optical Super-Resolution : using Structured Light to overcome the lowpass nature of an imaging system • how is Optical Super-Resolution different from Digital Super-Resolution ? • what is wrong with state-of-the-art in Optical Super-Resolution ? • Macroscopic OSR using Structured Light ( Uncalibrated ) • Depth estimation using Structured Light ( Uncalibrated ) • OSR + Depth estimation in a single setup ( Experimental Results )

  3. Structured Light and its applications What is Structured Light ? ..... periodic light patterns Why is it useful ? • Traditionally, used to recover depth maps & surface topology • Recently, used in microscopes to resolve spatial detail that cannot be resolved by the microscope

  4. Closer look at Depth from Structured LightPhase Measuring Profilometry DLP Principle • project a sinusoidal (periodic) pattern onto the scene, at a known angle • image of scene viewed from a different position AND-OR angle, reveals lateral displacements + frequency changes related to topological variations Mephisto 3D Scanner from 3D Dynamics Other DLP based SL-Scanners ViaLUX, GFM, 3D3, ShapeQuest SL hits from TI website Application Report DLPA021“Using the DLP Pico 2.0 Kit for Structured Light Applications” Blog entry “3D Metrology and Structured Light”, by Dennis Doane http://www.youtube.com/watch?v=854ZTvs8UoU http://www.youtube.com/watch?v=VGxEUKPNqcA

  5. Optical Super-Resolution using Structured Light has revolutionized microscopy in recent years Problem : Cameras behave like low-pass filters because their impulse response is real non-negative finite bandwidth & resolution Objective of Optical Super-Resolution : Improve the resolution of a camera without altering its physical parameters: Principle : shift frequencies outside the passband into the passband How ? modulate the amplitude of a periodic pattern with scene information

  6. Optical Super-Resolution using Structured Light How is it different from Digital Super-Resolution ? Optical Super-Resolution Recover spatial frequencies ( beyond the optical cutoff ) Digital Super-Resolution Recover spatial frequencies lost to aliasing ( but upto the optical cutoff ) See Optical Super-Resolution in action http://zeiss-campus.magnet.fsu.edu/tutorials/superresolution/hrsim/hrsim.swf

  7. Optical Super-Resolution using Structured LightPerspective & De-magnification Imaging & illumination systems in Structured Light-microscopy DO NOT experience significant perspective effects Perspective & de-magnification present a real challenge for macroscopic imaging /illumination systems such as commercial cameras/projectors scene-dependent distortion ( useful for recovering depth but not OSR ) imaging parallel lines on railroad track How do we eliminate the scene-dependent distortion ?

  8. Macroscopic OSR using Structured LightEliminating the scene-dependent distortion Solution-1 : Collocate the camera & projector, and illuminate the scene with a specific periodic patternDaniel A. Vaquero, RameshRaskar, Rogerio S. Feris, & Matthew Turk. ”A Projector-Camera Setup for Geometry-Invariant Frequency Demultiplexing”. In IEEE Computer Vision and Pattern Recognition (CVPR'09) Solution-2 : Coincide the camera & projector using a beam-splitterL. Zhang & S. K. Nayar, “Projection Defocus Analysis for Scene Capture and Image Display”, SIGGRAPH2006. Are we really shifting frequencies outside the passband of the optics, into the passband ? • “Macroscopic OSR” for imaging systems observing a 3D sceneunsolved since 1963 W. Lukosz and M. Marchand, "Optischen Abbildung Unter Ueberschreitung der Beugungsbedingten Aufloesungsgrenze," Opt. Acta 10, 241-255 (1963)

  9. Macroscopic OSR using Structured LightOur contributions • Identify a family of camera+projector setups that can realize OSR in macroscopic imaging , for arbitrary scenes • Unify existing embodiments of Structured Light • Single setup for recovering depth & realizing OSR Publications“Perspective Imaging under Structured Light”, accepted for publication in European Conference on Computer Vision , 2010 “Surpassing the Diffraction-limit of Digital Imaging Systems using Sinusoidal Illumination Patterns”, Computational Optical Sensing and Imaging, OSA Technical Digest (Optical Society of America), 2009 “A Method and Apparatus for Surpassing the Diffraction Limit in Imaging Systems”, filed patent super-resolved image raw image depth map

  10. Organization Imaging under “Structured Light” • what is “Structured Light” ? • estimating depth using “Structured Light” • Optical Super-Resolution : using Structured Light to overcome the lowpass nature of an imaging system • how is Optical Super-Resolution different from Digital Super-Resolution ? • what is wrong with state-of-the-art in Optical Super-Resolution ? • Macroscopic OSR using Structured Light ( Uncalibrated ) • Depth estimation using Structured Light ( Uncalibrated ) • OSR + Depth estimation in a single setup ( Experimental Results )

  11. Macroscopic OSR under Structured LightComplete Workflow • Identify the raw image and the exponentially modulated images Camera images under sinusoidal ilumination

  12. Macroscopic OSR under Structured LightComplete Workflow • Identify the frequency of the modulating pattern • After modulation, the DC component in shifts to the carrier frequency Camera images under sinusoidal ilumination The DC component of the super-resolved image must have zero phase. Use this to identify

  13. Macroscopic OSR under Structured LightComplete Workflow • Aliasing Management avoid aliasing demodulated spatial frequencies that exceed the detector Nyquist frequency Camera images under sinusoidal ilumination

  14. Macroscopic OSR under Structured LightComplete Workflow • Aliasing Management avoid aliasing demodulated spatial frequencies that exceed the detector Nyquist frequency Camera images under sinusoidal ilumination How is it done ? (sinc-interpolation) symmetrically increase the size of the modulated images by prior to demodulation

  15. Macroscopic OSR under Structured LightComplete Workflow • Aliasing Management avoid aliasing demodulated spatial frequencies that exceed the detector Nyquist frequency Camera images under sinusoidal ilumination Without aliasing management With aliasing management

  16. Macroscopic OSR under Structured LightComplete Workflow • Demodulation + Phase Compensation Camera images under sinusoidal ilumination • Quick Recap Any collocated/co-incident camera+projector setup can be used to recover spatial frequencies exceeding the bandwidth of an imaging system

  17. Organization Imaging under “Structured Light” • what is “Structured Light” ? • estimating depth using “Structured Light” • Optical Super-Resolution : using Structured Light to overcome the lowpass nature of an imaging system • how is Optical Super-Resolution different from Digital Super-Resolution ? • what is wrong with state-of-the-art in Optical Super-Resolution ? • Macroscopic OSR using Structured Light ( Uncalibrated ) • Depth estimation using Structured Light ( Uncalibrated ) • OSR + Depth estimation in a single setup ( Experimental Results )

  18. Recap : Depth from Structured LightPhase Measuring Profilometry DLP Principle • project a sinusoidal (periodic) pattern onto the scene, at a known angle • image of scene viewed from a different position AND-OR angle, reveals lateral displacements + frequency changes related to topological variations Mephisto 3D Scanner from 3D Dynamics Other DLP based SL-Scanners ViaLUX, GFM, 3D3, ShapeQuest SL hits from TI website Application Report DLPA021“Using the DLP Pico 2.0 Kit for Structured Light Applications” Blog entry “3D Metrology and Structured Light”, by Dennis Doane http://www.youtube.com/watch?v=854ZTvs8UoU http://www.youtube.com/watch?v=VGxEUKPNqcA

  19. Depth from Collocated Structured LightComplete Workflow To avoid ambiguities in phase unwrapping, 2 patterns ( 1 small frequency , 1 large frequency) are employed

  20. Organization Imaging under “Structured Light” • what is “Structured Light” ? • estimating depth using “Structured Light” • Optical Super-Resolution : using Structured Light to overcome the lowpass nature of an imaging system • how is Optical Super-Resolution different from Digital Super-Resolution ? • what is wrong with state-of-the-art in Optical Super-Resolution ? • Macroscopic OSR using Structured Light ( Uncalibrated ) • Depth estimation using Structured Light ( Uncalibrated ) • OSR + Depth estimation in a single setup ( Experimental Results )

  21. Experimental ResultsSetup-1 : vertically collocated camera+projector

  22. Experimental Results - OSRSetup-1 : vertically collocated camera+projector OSR is possible only in the horizontal direction

  23. Experimental Results – Estimating depthSetup-1 : vertically collocated camera+projector

  24. Experimental Results - OSRSetup-2 : non-collocated camera+projector

  25. Experimental ResultsSetup-2 : non-collocated camera+projector With aliasing management Without aliasing management

  26. Closing Arguments & Open IssuesPutting things in perspective • It is possible to resolve detail exceeding the BW of a macroscopic imaging system • There are camera+projector setups that can recover depth information + resolve detail exceeding the bandwidth of the imaging system • Can we super-reslove when the optical axes of the camera and projector are crossed ? • Can we accommodate aliasing during image capture ? Non-contact fingerprint scanning Non-contact archived document scanning Artwork authentication • Bar-code scanners • Counterfeit Bill Detection

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