Real-Time Projector Tracking on Complex Geometry Using Ordinary Imagery Tyler Johnson and Henry...
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Transcript of Real-Time Projector Tracking on Complex Geometry Using Ordinary Imagery Tyler Johnson and Henry...
Real-Time Projector Tracking on Complex
Geometry Using Ordinary Imagery
Tyler Johnson and Henry FuchsUniversity of North Carolina – Chapel Hill
ProCams June 18, 2007 - Minneapolis, MN
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Multi-Projector Display
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Dynamic Projector Repositioning
Make new portions of the scene visible
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Dynamic Projector Repositioning (2)
Increase spatial resolution or field-of-view
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Dynamic Projector Repositioning
Accidental projector bumping
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Goal
Given a pre-calibrated projector display, automatically compensate for changes in projector pose while the system is being used
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Previous Work
Class Active Passive
Technique Embedded Imperceptible Structured Light
Unmodified Imagery, Fixed Fiducials
References
Cotting04-05 Raskar03, Yang01
Online Projector Display Calibration Techniques
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Our Approach
Projector pose on complex geometry from unmodified user imagery without fixed fiducials
Rely on feature matches between projector and stationary camera.
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Overview
UpfrontCamera/projector calibrationDisplay surface estimation
At run-time in independent threadMatch features between projector and cameraUse RANSAC to identify false correspondencesUse feature matches to compute projector posePropagate new pose to the rendering
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Projector Pose Computation
Display Surface
Camera
Projector
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Difficulties
Projector and camera images are difficult to match
Radiometric differences, large baselines etc.
No guarantee of correct matchesNo guarantee of numerous strong features
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Feature Matching
Projector Image
Camera Image
P
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Feature Matching SolutionPredictive Rendering
Projector Image
Prediction Image Camera Image
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Predictive Rendering
Account for the followingProjector transfer functionCamera transfer functionProjector spatial intensity variation• How the brightness of the projector varies with FOV
Camera response to the three projector primaries
CalibrationProject a number of uniform white/color images• see paper for details
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Predictive Rendering Steps
Two steps: Geometric Prediction• Warp projector image to correspond with the
camera’s view of the imagery
Radiometric Prediction• Calculate the intensity that the camera will
observe at each pixel
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Step 1: Geometric Prediction
Two-Pass RenderingCamera takes place of viewer
Display Surface
Camera
Projector
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Step 2: Radiometric Prediction
Pixels of the projector image have been warped to their corresponding location in the camera image.Now, transform the corresponding projected intensity at each camera pixel to take into account radiometry.
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Radiometric Prediction (2)
Projector Intensity
(r,g,b)
Predicted Camera Intensity
(i)
Projector Response Projector IntensitySurface
Orientation/DistanceCamera Response
Spatial Intensity Scaling
θ
Proj. COP
r
2
cos
r
bgr III ,,
Projector Image
Prediction Image
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Prediction Results
Captured Camera Image Predicted Camera Image
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Prediction Results (2)
Errormean - 15.1 intensity levelsstd - 3.3 intensity levels
Contrast Enhanced Difference Image
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Video
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Implementation
Predictive RenderingGPU pixel shader
Feature detectionOpenCV
Feature matchingOpenCV implementation of Pyramidal KLT Tracking
Pose calculationNon-linear least-squares • [Haralick and Shapiro, Computer and Robot Vision, Vol.
2]• Strictly co-planar correspondences are not degenerate
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Matching Performance
Performance using geometric and radiometric prediction
Performance using only geometric prediction
Matching performance over 1000 frames for different types of imagery
Max. 200 feature detected per frame
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Tracking Performance
Pose estimation at 27 HzCommodity laptop• 2.13 GHz Pentium M• NVidia GeForce 7800 GTX GO
640x480 greyscale cameraMax. 75 feature matches/frame
Implement in separate thread to guarantee rendering performance
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Contribution
New projector display technique allowing rapid and automatic compensation for changes in projector pose
Does not rely on fixed fiducials or modifications to user imageryFeature-based, with predictive rendering used to improve matching reliabilityRobust against false stereo correspondencesApplicable to synthetic imagery with fewer strong features
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Limitations
Camera cannot be movedTracking can be lost due to
Insufficient featuresRapid projector motion
Affected by changes in environmental lighting conditionsRequires uniform surface
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Future Work
Extension to multi-projector displayWhich features belong to which projector?
Extension to intelligent projector modules
Cameras move with projector
Benefits of global illumination simulation in predictive rendering
[Bimber VR 2006]
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Thank You
Funding support: ONR N00014-03-1-0589Funding support: ONR N00014-03-1-0589DARWARS Training Superiority program DARWARS Training Superiority program
VIRTE – Virtual Technologies and Environments programVIRTE – Virtual Technologies and Environments program