Active Illumination for the RealWorld

Active illumination systems use a controllable light source and a light sensor to measure properties of a scene. For such a system to work reliably across a wide range of environments it must be able to handle the effects of global light transport, bright ambient light, interference from other active illumination devices, defocus, and scene motion. The goal of this thesis is to develop computational techniques and hardware arrangements to make active illumination devices based on commodity-grade components that work under real world conditions. We aim to combine the robustness of a scanning laser rangefinder with the speed, measurement density, compactness, and economy of a consumer depth camera. Towards this end, we have made four contributions. The first is a computational technique for compensating for the effects of motion while separating the direct and global components of illumination. The second is a method that combines triangulation and depth from illumination defocus cues to increase the working range of a projector-camera system. The third is a new active illumination device that can efficiently image the epipolar component of light transport between a source and sensor. The device can measure depth using active stereo or structured light and is robust to many global light transport effects. Most importantly, it works outdoors in bright sunlight despite using a low power source. Finally, we extend the proposed epipolar-only imaging technique to time-of-flight sensing and build a low-power sensor that is robust to sunlight, global illumination, multi-device interference, and camera shake. We believe that the algorithms and sensors proposed and developed in this thesis could find applications in a diverse set of fields including mobile robotics, medical imaging, gesture recognition, and agriculture. Acknowledgments I am extremely grateful to my advisor Srinivasa Narasimhan for all the guidance and support he provided during my doctoral studies. The lessons I’ve learnt working along with him have had a great impact on my thinking and the way I approach problems. I couldn’t have asked for a better mentor. I would like to thank Red Whittaker, Simon Lucey, Kyros Kutulakos and Wolfgang Heidrich for making the time to be part of my thesis committee and for all the advice and feedback they gave me. Parts of this thesis are the result of a very fruitful collaboration with Kyros and Matthew O’Toole from the University of Toronto and build upon some of their earlier work. Working with Matt has been a real privilege he has great ideas and also the ability to develop them in a systematic, rigorous way. Over the last few years Kyros has been like an unofficial co-advisor for me our weekly discussions and his insights have done a lot to shape this thesis. Special thanks to Red who has been a wonderful advocate for the work developed in this thesis. He has supported and encouraged efforts to investigate applications for our sensors in robotics, mining and agriculture. This work was done in the Illumination and Imaging Lab, a lab whose chief defect is that it is a gray, windowless room in the basement of Newell-Simon Hall. Its main redeeming feature is wonderful group of people working inside who have been my labmates in graduate school. Robert, Minh, Joe, Chao, Shumian, Jian and Suren have been great, intellectually stimulating company and they’ve always been willing to jump in and lend a hand while setting up experiments, collecting data or tracking down parts. Robert is also a co-inventor of FloorTennisTM and ScienceTimeTM, some of the finest afternoon diversions that have ever been created. A lot of the work in this thesis required skills and knowledge that I lacked and which no one in our lab had either. Luckily, the Robotics Institute is a place where people are incredibly generous with both their time and their expertise. During the early stages of the Episcan3D project, Christoph Mertz and John Kozac showed me how they had accessed the synchronization signals of the projector we were using which helped the project along immensely. Then, of course, there is Chuck Whittaker. Before Chuck, our prototype was a jumble of cameras and cables held together by prayers and duct tape. After Chuck, Episcan3D was a cool red box whose content never needed to be fiddled with or realigned again. My life in grad school was fun thanks to the company of a large and amazing group of friends. Abhijeet, Ajit, Apurva, Aranya, Aravindh, Arvind, Ashwati, Avinash, Chitra, Divya, Erle, Garg, Harsha, Harini, Ji, Jiuguang, Keshav, Lavanya, Maddali, Max, Mike, Nishtha, Riteja, Sahana, Sammy, Satya, Srinivas (the one who is not my advisor), Sudarshan, Suyash, Tommy, Toups, Uday, Utsav, Varun, Vas and Vinod a big thank you to all of you. Pittsburgh wouldn’t have been the same without the Youth Hostel, the zero Watt bulbs, the climbing, Dino, Mafia, or the “Table for 17 please” dinners and you are the people who made it all happen. The quizzing wasn’t bad either. Last, but definitely not least, I’d like to thank my parents and my sister without whose encouragement and support none of this would have been possible.