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Seamless Projection Overlaps using Image Warping and Intensity Blending

This presentation explores a method for creating seamless projection overlaps using image warping and intensity blending. It discusses the benefits of this approach and its applications in various display setups. Presented by Ramesh Raskar, Greg Welch, and Henry Fuchs from the University of North Carolina at Chapel Hill.

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Seamless Projection Overlaps using Image Warping and Intensity Blending

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  1. Seamless Projection Overlaps using Image Warping and Intensity Blending Presented by : …….. Ramesh Raskar, Greg Welch and Henry Fuchs University of North Carolina at Chapel Hill

  2. Acknowledgements • Office of the Future group at UNC Chapel Hill • Andrei State (sketches) • Support • NSF Science and Technology Center for Graphics and Visualization, USA • Advanced Networks and Services,National Tele-Immersion Initiative • Defense Advanced Research Projects Agency, USA • Intel Corporation

  3. Seamless Projection Overlaps Traditional Flexible Setup Display Surface Projectors P1 P3 P2 P2 P1 P3 Irregular display and projector configuration Well Defined Display Configuration

  4. Goal • High Resolution, Wide Field of View Display • Overlapping front projection system • Seamless display • Geometric Registration of overlaps • Intensity Blending near edges • Irregular display surface configuration P3 P2 P1

  5. Motivation :Office of the Future (UNC ‘98) • Irregular surfaces • No specific projector configuration

  6. Other Spatially Immersive Displays • 1. CAVE (UIC EVL) • Non-overlapping projections • Flat displays walls • Well-defined projection configuration

  7. Other Spatially Immersive Displays (Cont.) • 2. VisionDome (Alternate Realities) • Single Projector with expensive optics • Well defined display surfaces

  8. Other Spatially Immersive Displays (Cont.) • 3. Cylindrical Screens (Trimension, Panoram) • 3 Projectors with side-by-side rectangular overlap • Well defined display surface • Precise electro-mechanical setup

  9. Office of the Future (UNC ‘98) • Irregular surfaces • No specific projector configuration

  10. Office of the Future Configuration Irregular Surfaces Projectors Top View User Single User

  11. Our Approach • Calibration of display configuration using a video camera • Rendering using texture mapping hardware • Pair-wise registration and blending of projection overlaps

  12. Key Features • Display surfaces may not be flat walls • Projection axis not orthogonal to displays • Flexible projection configuration • Projector’s intrinsic or extrinsic parameters not needed • Generated image correct for a single ideal viewer’s location

  13. Calibration • Step 1 : Geometric Registration • Pre-distort images so that when projected they appear • Perspectively correct • Aligned with neighboring projection • Step 2 : Intensity Normalization • Blend images from overlapping projections

  14. Calibration Step 1 : Geometric Registration • Warping Images • For irregular display surfaces • Desired image is pre-warped • Warping function is found using a wide field of view camera (WFOV) • For flat display surfaces • Projected images related by a 3x2 transformation

  15. Calibration Step 1 : Geometric Registration • Warping Images for Irregular Display Surfaces • Keep the WFOV camera at ideal viewer’s location • Project dots with the projector one by one • Find mapping from projector image to camera image • Invert mapping to find the warping function

  16. Camera to Projector warping function Icamera(u,v) = Which projector pixel ? Display Surface WFOV Camera Observing a point on display surface Icamera(u,v)

  17. Camera to Projector warping function Icamera(u,v) = Iproj1(x,y), Iproj2(x,y) Display Surface Projector P1 Iproj1(x,y) Which projector pixel illuminated the same point on display surface ? Iproj2(x,y) Projector P2

  18. Calibration Step 2 : Intensity Normalization • Blending Projected Images • For irregular display surfaces • Projection overlap observed in camera image space • Assign intensity weights for projector pixels

  19. Intensity in Projector Overlap Display Surface Projector P1 Iproj1(x,y) How to make intensity in overlap region same as everywhere else ? WFOV Camera Icamera(u,v) Iproj2(x,y) Projector P2

  20. Intensity Normalization Projected Intensity Resultant Intensity Before Normalization P1 P2 Camera Scanline Projected Intensity Resultant Intensity After Normalization P1 P2 Camera Scanline

  21. Rendering • Two pass rendering method • First pass : Compute the desired image • Second pass : • Warping with standard OpenGL texture mapping • Intensity blending using Alpha channel of graphics hardware

  22. Results: correct view for one user Live Panoramic Video Image captured using a WFOV camera cluster

  23. Summary • Robust general purpose method to create seamless images • General configuration of projectors and display surfaces • High-resolution wide-field of view display using cluster of projectors • No expensive optics or electro-mechanical setup • One-time calibration procedure

  24. Applications • Office Scenarios, flexible setup • Dome shaped displays using cluster of projectors instead of expensive optics • Ease of setup for cylindrical projection screens using multiple projectors • Synthetic images or Video images on large display environments

  25. Ten Years from now .. • Light bulbs replaced by cheap projectors • Sufficient number of inexpensive cameras • Widely available texture mapping graphics hardware • Projectors, LCD panels to create ‘desktop’ instead of looking at a 21’ monitor

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