Dark Flash Photography

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Dark Flash Photography

• Dilip Krishnan
• Rob Fergus
• Dept. of Computer ScienceCourant Institute, New
  York University

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Taking Photos in Low Light Levels
Taking Photos in Low Light Levels
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Taking Photos in Low Light Levels

• Want to avoid sensor noise camera shake
  Possible solutions

Drawbacks
Can be used in conjunctionwith our approach
Our paper addresses these issues
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Dark Flash Photography

• Dark flash is 200 times dimmer than conventional

Ground truth
Reconstruction
2. Ambient image
1. Dark Flash image
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Key Challenges

1. How to add light to the scene without it being
   perceived by people.
2. How to obtain an image to true colors.

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Two Sensors
The Human Retina
Digital Camera Sensor
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Human Retina Spectral Sensitivity
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Human Retina Sensitivity Log Scale
NoteSteep fall off outside400-700nmrange
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Two Sensors
The Human Retina
Digital Camera Sensor
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Camera Spectral Sensitivity

• Spectral response curves for an unmodified DSLR

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Camera Spectral Sensitivity
Modify camera by 1. Remove IR-blocksensor
filter 2. Adding lens filter to remove IR
gt800nm ? Some sensitivityin UV IR just
outside visible
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Camera Spectral Sensitivity

• Comparison with human sensitivity curve
• Cameras response is significantly broader
• Possible to addlight without being easy
  perceived

Human Response Curve (not to scale)
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Dark Flash Emission Spectrum

• CameraSpectralSensitivity
• Dark FlashEmission

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Demonstration of Dark Flash

• Please look directly at the demonstration,NOT at
  the projection screens

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Comparison to Visible Flash

• Both flashes will fire simultaneously
• Both give comparable camera exposure
• Dark flash is 220x dimmer than visible flash

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Flash Safety

• Eye is most sensitive part of the body to UV
• Government TLVtables specify Hazard Factor
  safe limits
• ? Safety limit is 115,000 Flashesper day _at_ 1m
• Equivalent to being outside for 1/100th second

Dark Flash
Hazard Factor
Dark Light _at_ 1m for 1 sec
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Human Spectral Sensitivity Function
Shuman(?)
Vos 1978
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Log Human Spectral Sensitivity Function
log Shuman(?)
Vos 1978
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Camera Spectral Sensitivity

• Spectral response curves for DSLR with
  IR-blocksensor filter removed
• Too much IRsensitivity forour application?
  add partialIR block filterto lens

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Camera Spectral Sensitivity

• Spectral response curves for DSLR with
  IR-blocksensor filter removed IR lens filter
• Some sensitivityin UV IRjust outsidevisible

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