structured light sunlight
TRANSCRIPT
StructuredLight inSunlight
Manish Sinha
Introduction
Related Work
Concentrateand Scan
Experiment
Advantages
Disadvantages
Conclusion
Structured Light in Sunlight
Manish Sinha
Arizona State University
November 13, 2013
StructuredLight inSunlight
Manish Sinha
Introduction
Related Work
Concentrateand Scan
Experiment
Advantages
Disadvantages
Conclusion
Overview
1 Introduction
2 Related Work
3 Concentrate and Scan
4 Experiment
5 Advantages
6 Disadvantages
7 Conclusion
StructuredLight inSunlight
Manish Sinha
Introduction
Related Work
Concentrateand Scan
Experiment
Advantages
Disadvantages
Conclusion
Introduction to Structured light 3-D Reconstruction
Structured light based techniques: Reconstruction of anobject in 3-Dimension by projecting a structured light of aspecific pattern and using sensors to read the projectedlight on the object.
Challenges faced when using 3-D object reconstructionusing structured light in scenarios of high intensityambient light.
Old method: Exposing structured light all over the objectframe and taking f observations and averaging (Spreadand Average)
New method: Exposing structured light to a narrowcolumn of the object increases SNR and total timecomputation (Concentrate and Scan)
StructuredLight inSunlight
Manish Sinha
Introduction
Related Work
Concentrateand Scan
Experiment
Advantages
Disadvantages
Conclusion
Related Work
Structured light coding patterns
Examples are single line stripes and binary patterns. Inscenarios with extremely low SNR, optional SNR is achievedwith pattern with fewest possible intensity levels.
Spread and Average
For every image of the object, take ’f ’ frames and thencompute the average intensity, this way noise is reduced byfactor of
√f
Optical Ambient Illumination Suppression Methods
Using narrow spectral lasers, with narrow-band spectral filterand light source being polarized reduces the effect of intenseambient light.
StructuredLight inSunlight
Manish Sinha
Introduction
Related Work
Concentrateand Scan
Experiment
Advantages
Disadvantages
Conclusion
What is Concentrate and Scan
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 andambient light, then decodability condition needs to besatisfied for an acceptable SNR: Rl√
Ra≥ τ
λ where τ is
threashold SNR and λ is a constant for a given specificsetting.
Break the scene into C columns. Focus structured lightonto a smaller region of the scene called a block. A scenehas ’s’ blocks and a block has C/s columns.
Code each block separately and scan the focusedstructured light on the scene for all s blocks.
StructuredLight inSunlight
Manish Sinha
Introduction
Related Work
Concentrateand Scan
Experiment
Advantages
Disadvantages
Conclusion
Acquisition Time comparison
For spread and average, f frames [F1,F2, ...,Ff ], averagingintensity, noise can be reduced by factor of
√f , So
SNRavg =√f λ Rl
Ra. Since SNRavg should be more than τ ,
so f ≥ ( τλRl
)2Ra.
For spread and average, Nc is number of images, sonumber of calculations M = Nc * f, which means thatacquisition time runs in order of O(Ra)
for Concentrate and Scan, if the scene is broken into Ccolumns with each block of K columns, then s = C/K. Inthat case total illumination is Rl
CK . Substituting that in
incredibility condition. Kopt = λCτ
Rl√Ra
For Concentrate and Scan, Nk is number of blocks, soMcs = Nk ∗ C
K , then substituting Kopt , Mcs = Nkτ
λRl
√Ra.
We see acquisition time runs in order of O(√Ra)
StructuredLight inSunlight
Manish Sinha
Introduction
Related Work
Concentrateand Scan
Experiment
Advantages
Disadvantages
Conclusion
Hardware Prototype
StructuredLight inSunlight
Manish Sinha
Introduction
Related Work
Concentrateand Scan
Experiment
Advantages
Disadvantages
Conclusion
Concentrate and Scan versus Spread and Average
StructuredLight inSunlight
Manish Sinha
Introduction
Related Work
Concentrateand Scan
Experiment
Advantages
Disadvantages
Conclusion
Advantages of Concentrate and Scan
For fixed light budget and same SNR, number ofmeasurements is O(
√Ra) instead of O(Ra) in Spread and
Average.
The improvements in SNR via Concentrate and Scan isway more than the improvements in SNR via opticalmethods.
For typical low power projectors, the Concentrate andScan approach requires 1-2 orders of magnitude loweracquisition time than the existing schemes, for all outdoorambient illuminance levels.
StructuredLight inSunlight
Manish Sinha
Introduction
Related Work
Concentrateand Scan
Experiment
Advantages
Disadvantages
Conclusion
Disadvantages of Concentrate and Scan
Lower structured light power: Concentrate and Scanfails when the structured light incident on the object haslower power. To put it in other words, when the ambientlight is intense, the decodability condition is not satisfied.
Loss of light when focussing: Some light is lost by thedevice which focuses structured light on the block of theobject.
Expensive focussing equipment: Since we cannotincrease the power output of structured light source, weneed extra apparatus just to focus light properly on theobject and scan it. Moving parts devices are more prone tofailures.
StructuredLight inSunlight
Manish Sinha
Introduction
Related Work
Concentrateand Scan
Experiment
Advantages
Disadvantages
Conclusion
Summary and Conclusion
Spread and Average with optical suppression methods isinsufficient for scenes with high ambient light intensity.
We need to focus light on narrow block and scan thescene for overcoming high ambient light intensity.
Concentrate and Scan is faster than Spread and Averagemethod for same light budget.