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Polarization- Beneficial for Visibility Enhancement?. Tali Treibitz, Yoav Y. Schechner Technion, Israel. Visibility in Haze. Treibitz & Schechner, Polarization- Beneficial for Visibility Enhancement?. L. object. total intensity. object radiance. airlight. I. A. D.
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Polarization- Beneficial for Visibility Enhancement? Tali Treibitz, Yoav Y. Schechner Technion, Israel
Visibility in Haze Treibitz & Schechner, Polarization- Beneficial for Visibility Enhancement?
L object total intensity object radiance airlight I A D direct transmission scattering 0 z 1 0 z
Visibility in Haze Treibitz & Schechner, Polarization- Beneficial for Visibility Enhancement?
best polarized image Haze Through a Polarizer Treibitz & Schechner, Polarization- Beneficial for Visibility Enhancement?
best polarized image Haze Through a Polarizer increased exposure time single frame- used by photographers Treibitz & Schechner, Polarization- Beneficial for Visibility Enhancement?
best polarized image worst polarized image Haze Through a Polarizer post-processing 2 frames two frames- Schechner et al. Treibitz & Schechner, Polarization- Beneficial for Visibility Enhancement?
Is it worth using a polarizer? best polarized image unpolarized image post-processing 2 frames • goal: object detection • local contrast stretch- OK Treibitz & Schechner, Polarization- Beneficial for Visibility Enhancement?
9 Method-Independent Visibility Limits • Noise induces a resolution cutoff, without imaging blur • Independent of post processing detection no detection system input SNR frequency “Recovery Limits in Pointwise Degradations”, Treibitz & Schechner, ICCP ’09
Method-Dependent Performance increase acquisition time? gain SNR? constraint: equal acquisition time related works:
Noise Model photon noise dominates courtesy of Brian Curless Treibitz & Schechner, Polarization- Beneficial for Visibility Enhancement?
Degradations in Haze deterministic random reduce SNR even if known SNRhaze=
Using a Single Polarized Image I best Best polarized image degree of polarization
acquisition time = exposure time X number of frames technical details in the paper SNR Comparison equal acquisition time
a single saturated image SNRpolarized SNRunpolarized maximal value in nature Treibitz & Schechner, Polarization- Beneficial for Visibility Enhancement?
same total acquisition time SNRpolarized SNRunpolarized p<0.4 in our experiments maximal value in nature Treibitz & Schechner, Polarization- Beneficial for Visibility Enhancement?
Experiment larger FOV - average of 2 images same total acquisition time Treibitz & Schechner, Polarization- Beneficial for Visibility Enhancement?
Polarization-Based Dehazing I best Best polarized image degree of polarization
Polarization-Based Dehazing I worst Worst polarized image degree of polarization
technical details in the paper SNR Comparison dehazing equal acquisition time optimal exposures
“In defense of contrast stretch” Our analysis: higher noise in dehazed image dehazing Treibitz & Schechner, Polarization- Beneficial for Visibility Enhancement?
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?
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?
Summary • Case study of method comparison • Performance trade-offs • Unpolarized images are best(equal acquisition time) Treibitz & Schechner, Polarization- Beneficial for Visibility Enhancement?