Time of Flight Cameras - Refael Whyte

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  • Currentcolor imaging technology only provides clues about the depth in the scene. Only social cues like the size of objects and shadows.
  • Time of flight cameras measure the depth for each pixel. This is an example figure from a time of flight camera. Each pixel is located in X,Y,Z in space. Person infront of the scene.
  • Phase translates to distance. Measure phase because measuring direct time of flight is hard.
  • Really say that four frames are required. Say something about motion.
  • Talk about the noise. The black table cloth returns less light therefore is more noisy.
  • Say the modulation frequency is the length of the pulse. The shorter the pulse the more precision the measurements however phase wrapping.
  • Add comments about mixed pixels.
  • Talk about how we are exploring other areas for ToF. Medical imaging.
  • Time of Flight Cameras - Refael Whyte

    1. 1. MIT Media Lab Camera Culture Introduction to Time-of-Flight Range Imaging Refael Whyte
    2. 2. MIT Media Lab Camera Culture Why Depth? • Color photos have limited depth information
    3. 3. MIT Media Lab Camera Culture Time-of-Flight Cameras 18 October 2013 © THE UNIVERSITY OF WAIKATO • TE WHARE WANANGA O WAIKATO 3
    4. 4. MIT Media Lab Camera Culture Measuring Distance • Illuminate scene with amplitude modulated light. • Phase difference between transmitted and reflected light encodes distance. • Transmitted and returning light is correlated to measure distance. 18 October 2013 © THE UNIVERSITY OF WAIKATO • TE WHARE WANANGA O WAIKATO 4
    5. 5. MIT Media Lab Camera Culture Measuring Distance • Returning light is correlated with reference waveform. • Reference waveform is phase shifted • Measured points fit a sine wave. 5
    6. 6. MIT Media Lab Camera Culture Correlation Function
    7. 7. MIT Media Lab Camera Culture Measuring Distance
    8. 8. MIT Media Lab Camera Culture Real Data • Measured correlation waveform of one pixel • Compute phase and amplitude from FFT.
    9. 9. MIT Media Lab Camera Culture Camera Data • Phase and amplitude images, 120x160 sensor.
    10. 10. MIT Media Lab Camera Culture Measurement Errors
    11. 11. MIT Media Lab Camera Culture Multipath • Multiple propagation paths. • In scene paths and lens flare effects. • Still an unsolved problem. Use low reflective material around objects of interest to mitigate 18/10/2013 © THE UNIVERSITY OF WAIKATO • TE WHARE WANANGA O WAIKATO 11
    12. 12. MIT Media Lab Camera Culture Multipath • The measured pixels value is the sum of both components on the complex plane. • Reflect table tops and floors can see reflection in the amplitude image.
    13. 13. MIT Media Lab Camera Culture Other Sources • Temperature drift. • Jitter. Jitter in the modulation signal limits precision. • Photon shot noise in pixel structure. Is assumed to be an independent guassian noise source. • Readout noise. Noise added by ADC and readout process. • Harmonic aliasing impacts accuracy.
    14. 14. MIT Media Lab Camera Culture Time-of-Flight at MIT • Access to commercial Time of flight cameras and custom built ones • Commercial ones from: Softkinetic, PMD and Mesa Imaging
    15. 15. MIT Media Lab Camera Culture Coke Bottle Light Sweep • Visualization of light in a coke bottle http://www.youtube.com/watch?v=fSqFWcb4rE • Light sweep with ToF Camera https://sites.google.com/site/tofvid/ • Similar results 1000x reduction in cost of hardware.
    16. 16. MIT Media Lab Camera Culture Time of Flight Applications • Next generation Kinect for Xbox One. http://www.youtube.com/watch?v=Hi5kMNfgDS 4 • Object Scanning http://www.youtube.com/watch?v=IXr9zqz6Bjc • Hand tracking http://www.youtube.com/watch?v=Qj4ymzTNw Dw • Other http://www.youtube.com/watch?v=eAlSfEqBBhM
    17. 17. MIT Media Lab Camera Culture Other Applications • • • • Manufacturing Automation Robotic navigation. Rumoured to being developed for phones so the sky is the limit.

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