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LIGHT TRANSPORT SIMULATION in REFLECTIVE DISPLAYS By LIGHT TRANSPORT SIMULATION IN REFLECTIVE DISPLAYS by Zhanpeng Feng, B.S.E.E., M.S.E.E. A Dissertation In ELECTRICAL ENGINEERING DOCTOR OF PHILOSOPHY Dr. Brian Nutter Chair of the Committee Dr. Sunanda Mitra Dr. Tanja Karp Dr. Richard Gale Dr. Peter Westfall Peggy Gordon Miller Dean of the Graduate School May, 2012 Copyright 2012, Zhanpeng Feng Texas Tech University, Zhanpeng Feng, May 2012 ACKNOWLEDGEMENTS The pursuit of my Ph.D. has been a rather long journey. The journey started when I came to Texas Tech ten years ago, then took a change in direction when I went to California to work for Qualcomm in 2006. Over the course, I am privileged to have met the most amazing professionals in Texas Tech and Qualcomm. Without them I would have never been able to finish this dissertation. I begin by thanking my advisor, Dr. Brian Nutter, for introducing me to the brilliant world of research, and teaching me hands on skills to actually get something done. Dr. Nutter sets an example of excellence that inspired me to work as an engineer and researcher for my career. I would also extend my thanks to Dr. Mitra for her breadth and depth of knowledge; to Dr. Karp for her scientific rigor; to Dr. Gale for his expertise in color science and sense of humor; and to Dr. Westfall, for his great mind in statistics. They have provided me invaluable advice throughout the research. My colleagues and supervisors in Qualcomm also gave tremendous support and guidance along the path. Tom Fiske helped me establish my knowledge in optics from ground up and taught me how to use all the tools for optical measurements. I was amazed in a number of circumstances that he discovered software bugs by just a quick look at the data. My special thanks go to Rick Brinkley, for not only giving me time and room in busy work schedules, but for also making me believe that obtaining a doctoral degree is a significant achievement, especially when I was in doubt. I also would like to express my appreciation to Bill Cummings, Chris Hogh, Jennifer Gille, Alok Govil, Behnam Bastani, Russel Martin, and Ibrahim Sezan, for their support and inspiring discussions. My gratitude towards my family is beyond words. I would like to thank my parents, Xiushan Feng and Bixia Feng, my sister, Yingtao Feng, and my brother in law, Xiaodong Pan, for always standing behind me. When I was feeling lost and discouraged, your love and support were always there to give me strength. During the final write-up stage, the stress of long hours of writing were put at ease by home- cooked delicious meals and a warm soup at my desk. I know you have always been proud of me, and I want you to know that I am proud to be your son and brother. ii Texas Tech University, Zhanpeng Feng, May 2012 I am filled with thankfulness for the most amazing thing that has ever happened to my life, the birth of my little girl, Yongqing Feng. No matter how challenging it is to be swamped with work and research, a simple thought of your smile helps me regain my confidence and energy. Finally, I want to thank my wife, Yihua Yuan, for coming to my life. Thank you for all the long flights between Texas and California every month for over two years. Thank you for making the sacrifice to stay with me in the United States. Thank you for bringing our wonderful daughter to the world. With you, I rediscovered the goal of life. I hope we will always hold hands as tight as now and build a bright future together. iii Texas Tech University, Zhanpeng Feng, May 2012 TABLE OF CONTENTS ACKNOWLEDGEMENTS ................................................................................................ ii ABSTRACT ....................................................................................................................... vi LIST OF FIGURES ......................................................................................................... viii LIST OF TABLES ............................................................................................................. xi CHAPTER 1. INTRODUCTION ....................................................................................................... 1 2. BACKGROUND ......................................................................................................... 4 Assumptions .................................................................................................................... 4 Interference and Interferometric Displays ....................................................................... 5 Monte Carlo Ray Tracing ................................................................................................ 8 Radiometry .................................................................................................................. 8 Ray Tracing ............................................................................................................... 10 Rendering Equation ................................................................................................... 11 Monte Carlo Integration ............................................................................................ 13 Reflectance Modeling ................................................................................................... 15 Microscopic Geometry of Surfaces ........................................................................... 16 BRDF and Surface Reflection ................................................................................... 19 BSSRDF and Subsurface Scattering .......................................................................... 22 Summary ....................................................................................................................... 27 3. MODELING REFLECTIVE DISPLAYS ................................................................. 28 Introduction ................................................................................................................... 28 Related Work................................................................................................................. 29 Front of Screen .............................................................................................................. 31 Modeling and Measuring a Diffuser ............................................................................. 33 Display Pixel Array ....................................................................................................... 43 Summary ....................................................................................................................... 44 4. MONTE CARLO RAY TRACING IN REFLECTIVE DISPLAYS ........................ 45 Introduction ................................................................................................................... 45 Path Tracing .................................................................................................................. 46 Stratified Sampling ........................................................................................................ 47 iv Texas Tech University, Zhanpeng Feng, May 2012 Importance Sampling .................................................................................................... 49 Simulation with Uniform Sampling, Cosine Sampling, and Ward Sampling ............... 53 Summary ....................................................................................................................... 57 5. SIMULATING DISPLAY PERFORMANCE .......................................................... 58 Introduction ................................................................................................................... 58 Software Architecture ................................................................................................... 59 Reflectance of Display Pixels ....................................................................................... 61 Color Gamut and Contrast Ratio .................................................................................. 62 Simulation Results and Measured Data ........................................................................ 65 Typical Lighting Conditions for Display Simulation .................................................... 72 Impact of Front Surface Reflection ............................................................................... 76 Diffuser with Different Haze Values ............................................................................ 76 Auxiliary Lighting (Front Light) ................................................................................... 78 Daylight Readability ..................................................................................................... 80 Summary ....................................................................................................................... 83 6. CONCLUSIONS AND FUTURE WORK ................................................................ 84 Summary of Contributions ............................................................................................ 84 Future Work .................................................................................................................. 85 REFERENCES ................................................................................................................. 88 v Texas Tech University, Zhanpeng Feng, May 2012 ABSTRACT In the last several years, reflective displays have gained substantial popularity in mobile devices such as e-readers, because of their significant advantages in power consumption
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