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Automatic Projector Calibration with Embedded Light Sensors
Johnny C. Lee1,2
Paul H. Dietz2
Dan Maynes-Aminzade2,3
Ramesh Raskar2
Scott E. Hudson1
1Carnegie Mellon University2Mitsubishi Electric Research Labs3Stanford University
Santa Fe, NM UIST 2004
Introduction to Projection
Introduction to Projection
Projector Calibration
Projector Calibration
Our Approach
- Embed light sensors into the target surface
- optical fibers channel light energy from each corner to sensors
- USB connection to the PC
- White front surface hides fibers and acts as a light diffuser
Calibration Demo
Demonstration of calibration process
Gray Code Patterns- Binary sequence where only 1-bit changes
from one entry to the next.- Robust spatial encoding property
• Frequently used in Range-Finding systems
Binary Gray
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
0000
0001
0011
0010
0110
0111
0101
0100
1100
1101
1111
1110
1010
1011
1001
1000
Binary Gray
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
0000
0001
0011
0010
0110
0111
0101
0100
1100
1101
1111
1110
1010
1011
1001
1000
Binary Gray
Binary Gray
Binary Gray
Binary Gray
Binary Gray
Binary Gray
Binary Gray
Binary Gray
Binary Gray
Binary Gray
Binary Gray
Binary Gray
Scalability and Robustness
- Pattern count = log2(pixels)
- Constant time with respect to # of sensors- Decoding location requires only one XOR
operation per location bit (cheap & fast)- Robust against inter-pixel sensor positioning- Robust against super-pixel size sensors- Accurate to the nearest pixel when in focus- Degrades gracefully in under defocusing- Strong angular robustness
Angular Robustness & Mirrors
Demonstration Video
Optical Path
Optical path between the projector and the sensor does not need to be known.
Pixel location of a sensor can be found so long as there exists a path.
Additional sensors in the target surface can increase robustness to partial occlusion.
Application Demonstrations
Demonstration Video
Research Applications
Everywhere Displays, IBM Digital Merchandising, MERL
ShaderLamps, projector AR, UNC/MERL
Other Applications
Cheap, light-weight displays
Projector array stitching
- data walls
- planetariums
Redundant projector alignment
- shadow reduction
- stereoscopic displays
- increasing brightness
- high-dynamic range display
Trade OffsDigital correction inherently sacrifices
pixels and resamples the image.– Image filtering– Higher resolution projectors– Pan-Tilt-Zoom projectors (preserve pixel
density)– Optical correction
Requires instrumented surface– Not a problem for some
high QoS applications– Removable/reusable wireless
calibration tags
Future WorkInteractive Rates - Movable Screens
– High speed projection (DLP)– n-ary and RGB Gray Codes– Adaptive Patterns
Imperceptible calibration– High speed steganography– Infrared
Multiple projectors– Smart rooms– 3D positioning
Concluding remarks
• Robust• Fast• Accurate• Low-Cost• Scalable• Applicable in HCI and out
Contact InfoJohnny Chung [email protected]
Thanks!
Haptic Pen: A Tactile Feedback Stylus for Touch Screens
Wednesday 3pm session
Homography
Four sensor coordinates are used to compute a homography – (loosely) a transformation between two coordinate spaces.
• Automatically flips image in the presence of mirrors.
• Works with OpenGL and DirectX matrix stacks for real-time warping on low-cost commodity hardware.
• Warping extends beyond the bounds of the sensors (internal feature registration, characterization)
• If more than 4 sensors are use, sub-pixel accuracy can be achieved through best-fit solutions
vs. Camera Based Approach Standard computer vision problems
– Background separation– Variable lighting conditions– Material reflectance properties– Non-planar/Non-continuous surfaces can be difficult
Accurate registration to world features requires high resolution cameras– Expensive (and high-speed is even more expensive)– High-computational overhead (Pentium vs. PIC)
Rigid camera-projector geometry– Requires calibration– Zooming may be problematic
Not as flexible– Projector stitching/Redundancy– ShaderLamps/Non-planar surfaces