Structured
Light in
Sunlight
Manish Sinha
Introduction
Related Work

Structured Light in Sunlight

Concentrate
and Scan
Ex...
Overview
Structured
Light in
Sunlight
Manish Sinha
Introduction

1 Introduction
2 Related Work

Related Work
Concentrate
a...
Introduction to Structured light 3-D Reconstruction
Structured
Light in
Sunlight
Manish Sinha
Introduction
Related Work
Co...
Related Work
Structured
Light in
Sunlight
Manish Sinha
Introduction
Related Work
Concentrate
and Scan

Structured light co...
What is Concentrate and Scan
Structured
Light in
Sunlight
Manish Sinha
Introduction
Related Work
Concentrate
and Scan
Expe...
Acquisition Time comparison
Structured
Light in
Sunlight
Manish Sinha
Introduction
Related Work
Concentrate
and Scan
Exper...
Hardware Prototype
Structured
Light in
Sunlight
Manish Sinha
Introduction
Related Work
Concentrate
and Scan
Experiment
Adv...
Concentrate and Scan versus Spread and Average
Structured
Light in
Sunlight
Manish Sinha
Introduction
Related Work
Concent...
Advantages of Concentrate and Scan
Structured
Light in
Sunlight
Manish Sinha
Introduction
Related Work
Concentrate
and Sca...
Disadvantages of Concentrate and Scan
Structured
Light in
Sunlight
Manish Sinha
Introduction
Related Work
Concentrate
and ...
Summary and Conclusion
Structured
Light in
Sunlight
Manish Sinha
Introduction
Related Work
Concentrate
and Scan
Experiment...
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Structured Light Sunlight

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Paper Abstract:
Strong ambient illumination severely degrades the performance of structured light based techniques. This is especially true in outdoor scenarios, where the structured light sources have to compete with sunlight, whose power is often 2-5 orders of magnitude larger than the projected light. In this paper, we propose the concept of light-concentration to overcome strong ambient illumination. Our key observation is that given a fixed light (power) budget, it is always better to allocate it sequentially in several portions of the scene, as compared to spreading it over the entire scene at once.

For a desired level of accuracy, we show that by distributing light appropriately, the proposed approach requires 1-2 orders lower acquisition time than existing approaches. Our approach is illumination-adaptive as the optimal light distribution is determined based on a measurement of the ambient illumination level. Since current light sources have a fixed light distribution, we have built a prototype light source that supports flexible light distribution by controlling the scanning speed of a laser scanner. We show several high quality 3D scanning results in a wide range of outdoor scenarios. The proposed approach will benefit 3D vision systems that need to operate outdoors under extreme ambient illumination levels on a limited time and power budget.

Paper Link: http://www1.cs.columbia.edu/CAVE/publications/pdfs/Gupta_ICCV13a.pdf

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Structured Light Sunlight

  1. 1. Structured Light in Sunlight Manish Sinha Introduction Related Work Structured Light in Sunlight Concentrate and Scan Experiment Manish Sinha Advantages Disadvantages Conclusion Arizona State University manish.sinha@asu.edu November 13, 2013
  2. 2. Overview Structured Light in Sunlight Manish Sinha Introduction 1 Introduction 2 Related Work Related Work Concentrate and Scan 3 Concentrate and Scan Experiment Advantages 4 Experiment Disadvantages Conclusion 5 Advantages 6 Disadvantages 7 Conclusion
  3. 3. Introduction to Structured light 3-D Reconstruction Structured Light in Sunlight Manish Sinha Introduction Related Work Concentrate and Scan Experiment Advantages Disadvantages Conclusion Structured light based techniques: Reconstruction of an object in 3-Dimension by projecting a structured light of a specific pattern and using sensors to read the projected light on the object. Challenges faced when using 3-D object reconstruction using structured light in scenarios of high intensity ambient light. Old method: Exposing structured light all over the object frame and taking f observations and averaging (Spread and Average) New method: Exposing structured light to a narrow column of the object increases SNR and total time computation (Concentrate and Scan)
  4. 4. Related Work Structured Light in Sunlight Manish Sinha Introduction Related Work Concentrate and Scan Structured light coding patterns Examples are single line stripes and binary patterns. In scenarios with extremely low SNR, optional SNR is achieved with pattern with fewest possible intensity levels. Spread and Average Experiment Advantages Disadvantages Conclusion For every image of the object, take ’f ’ frames and then compute √ average intensity, this way noise is reduced by the factor of f Optical Ambient Illumination Suppression Methods Using narrow spectral lasers, with narrow-band spectral filter and light source being polarized reduces the effect of intense ambient light.
  5. 5. What is Concentrate and Scan Structured Light in Sunlight Manish Sinha Introduction Related Work Concentrate and Scan Experiment Advantages Disadvantages Conclusion An intensity of the light at a scene is: I = Il + Ia + η. The goal is to extract the Il component. The SNR is Il /η If Rl and Ra are illumination value for structured light and ambient light, then decodability condition needs to be Rl τ satisfied for an acceptable SNR: √R ≥ λ where τ is a threashold SNR and λ is a constant for a given specific setting. Break the scene into C columns. Focus structured light onto a smaller region of the scene called a block. A scene has ’s’ blocks and a block has C/s columns. Code each block separately and scan the focused structured light on the scene for all s blocks.
  6. 6. Acquisition Time comparison Structured Light in Sunlight Manish Sinha Introduction Related Work Concentrate and Scan Experiment Advantages Disadvantages Conclusion For spread and average, f frames [F1 , F2 , ...,√f ], averaging F intensity, noise can be reduced by factor of f , So √ R l SNRavg = f λ Ra . Since SNRavg should be more than τ , τ so f ≥ ( λRl )2 Ra . For spread and average, Nc is number of images, so number of calculations M = Nc * f, which means that acquisition time runs in order of O(Ra ) for Concentrate and Scan, if the scene is broken into C columns with each block of K columns, then s = C/K. In C that case total illumination is Rl K . Substituting that in Rl incredibility condition. Kopt = λC √R τ a For Concentrate and Scan, Nk is number of blocks, so √ C τ Mcs = Nk ∗ K , then substituting Kopt , Mcs = Nk λRl Ra . √ We see acquisition time runs in order of O( Ra )
  7. 7. Hardware Prototype Structured Light in Sunlight Manish Sinha Introduction Related Work Concentrate and Scan Experiment Advantages Disadvantages Conclusion
  8. 8. Concentrate and Scan versus Spread and Average Structured Light in Sunlight Manish Sinha Introduction Related Work Concentrate and Scan Experiment Advantages Disadvantages Conclusion
  9. 9. Advantages of Concentrate and Scan Structured Light in Sunlight Manish Sinha Introduction Related Work Concentrate and Scan Experiment Advantages Disadvantages Conclusion For fixed light budget and same SNR, number of √ measurements is O( Ra ) instead of O(Ra ) in Spread and Average. The improvements in SNR via Concentrate and Scan is way more than the improvements in SNR via optical methods. For typical low power projectors, the Concentrate and Scan approach requires 1-2 orders of magnitude lower acquisition time than the existing schemes, for all outdoor ambient illuminance levels.
  10. 10. Disadvantages of Concentrate and Scan Structured Light in Sunlight Manish Sinha Introduction Related Work Concentrate and Scan Experiment Advantages Disadvantages Conclusion Lower structured light power: Concentrate and Scan fails when the structured light incident on the object has lower power. To put it in other words, when the ambient light is intense, the decodability condition is not satisfied. Loss of light when focussing: Some light is lost by the device which focuses structured light on the block of the object. Expensive focussing equipment: Since we cannot increase the power output of structured light source, we need extra apparatus just to focus light properly on the object and scan it. Moving parts devices are more prone to failures.
  11. 11. Summary and Conclusion Structured Light in Sunlight Manish Sinha Introduction Related Work Concentrate and Scan Experiment Advantages Disadvantages Conclusion Spread and Average with optical suppression methods is insufficient for scenes with high ambient light intensity. We need to focus light on narrow block and scan the scene for overcoming high ambient light intensity. Concentrate and Scan is faster than Spread and Average method for same light budget.

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