Tali Treibitz, Yoav Y. Schechner

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Polarization- Beneficial for Visibility
Enhancement?

• Tali Treibitz, Yoav Y. Schechner
• Technion, Israel

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Visibility in Haze
Treibitz Schechner, Polarization- Beneficial
for Visibility Enhancement?
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1
0
z
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Visibility in Haze
Treibitz Schechner, Polarization- Beneficial
for Visibility Enhancement?
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Haze Through a Polarizer
Treibitz Schechner, Polarization- Beneficial
for Visibility Enhancement?
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Haze Through a Polarizer
increased exposure time
single frame- used by photographers
Treibitz Schechner, Polarization- Beneficial
for Visibility Enhancement?
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Haze Through a Polarizer
post-processing 2 frames
two frames- Schechner et al.
Treibitz Schechner, Polarization- Beneficial
for Visibility Enhancement?
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• goal object detection
• local contrast stretch- OK

Treibitz Schechner, Polarization- Beneficial
for Visibility Enhancement?
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Method-Independent Visibility Limits

• Noise induces a resolution cutoff, without
  imaging blur
• Independent of post processing

no detection
detection
system input SNR
frequency
Recovery Limits in Pointwise Degradations,
Treibitz Schechner, ICCP 09
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Method-Dependent Performance
increase acquisition time?
gain SNR?
constraint equal acquisition time
related works
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Noise Model
photon noise dominates
courtesy of Brian Curless
Treibitz Schechner, Polarization- Beneficial
for Visibility Enhancement?
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Degradations in Haze
deterministic
random
reduce SNR even if known
SNRhaze
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Using a Single Polarized Image
I
best
Best polarized image
degree of polarization
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SNR Comparison
technical details in the paper
?
?
equal acquisition time
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a single saturated image
SNRpolarized
SNRunpolarized
maximal value in nature
Treibitz Schechner, Polarization- Beneficial
for Visibility Enhancement?
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same total acquisition time
SNRpolarized
SNRunpolarized
plt0.4 in our experiments
maximal value in nature
Treibitz Schechner, Polarization- Beneficial
for Visibility Enhancement?
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Experiment
larger FOV
- average of 2 images
same total acquisition time
Treibitz Schechner, Polarization- Beneficial
for Visibility Enhancement?
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Polarization-Based Dehazing
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best
Best polarized image
degree of polarization
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Polarization-Based Dehazing
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worst
Worst polarized image
degree of polarization
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SNR Comparison
technical details in the paper
dehazing
?
equal acquisition time
optimal exposures
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In defense of contrast stretch
Our analysis higher noise in dehazed image
dehazing
Treibitz Schechner, Polarization- Beneficial
for Visibility Enhancement?
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Advantages of Polarization-Based Dehazing
recover distance map

• contrast stretch in non-uniform distances
• color
• compensate for attenuation

• Goal is object detection
• Local contrast stretch on areas with similar
  distances

Treibitz Schechner, Polarization- Beneficial
for Visibility Enhancement?
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Single Image Dehazing

• Tan, CVPR 08
• Fattal, SIGGRAPH 08
• Kopf et al., SIGGRAPH Asia 08
• He et al., CVPR 09 (tomorrow- best paper
  session)

• our context
• Polarization does not give SNR advantage
• Puts these methods in a more favorable position

Treibitz Schechner, Polarization- Beneficial
for Visibility Enhancement?
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Summary

• Case study of method comparison
• Performance trade-offs
• Unpolarized images are best (equal acquisition
  time)

Treibitz Schechner, Polarization- Beneficial
for Visibility Enhancement?