dark flash photography dilip krishnan rob fergus dept. of computer science courant institute, new...
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Dark Flash Photography
Dilip KrishnanRob Fergus
Dept. of Computer ScienceCourant Institute,
New York University
Taking Photos in Low Light Levels
Taking Photos in Low Light Levels
Taking Photos in Low Light Levels
Want to avoid sensor noise & camera shake Possible solutions:
1. Large Aperture Lens
Expensive, Depth-of Field issues
Drawbacks:
2. Image stabilization
Only gives a few extra stops of exposure
3. Camera flash
Active method, Disturbs Scene
Can be used in conjunctionwith our approach Our paper addresses
these issues
• Dark flash is ~200 times dimmer than conventional Ground truthReconstruction2. Ambient image
Dark Flash Photography
1. Dark Flash image
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.
Digital Camera Sensor
Two Sensors
The Human Retina
Human Retina Spectral Sensitivity
Human Retina Sensitivity – Log Scale
Note:Steep falloff outside400-700nm
range
Digital Camera Sensor
Two Sensors
The Human Retina
Camera Spectral Sensitivity
• Spectral response curves for an unmodified DSLR
Modify camera by:
1. Remove IR-blocksensor filter
2. Adding lens filter to remove IR >800nm
Some sensitivityin UV & IR just outside visible
Camera Spectral Sensitivity
Camera Spectral Sensitivity
Human Response Curve (not to scale)
• Comparison with human sensitivity curve
• Camera’s response is significantly broader
• Possible to addlight without being easy perceived
Dark Flash Emission Spectrum
CameraSpectralSensitivity
Dark FlashEmission
Demonstration of Dark Flash
• Please look directly at the demonstration,NOT at the projection screens
Comparison to Visible Flash
• Both flashes will fire simultaneously• Both give comparable camera exposure
• Dark flash is ~220x dimmer than visible flash
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 @ 1m
• Equivalent to being outside for 1/100th second
Dark Flash
Dark Light @ 1m for
~1 sec
Hazard Factor
Human Spectral Sensitivity Function
Vos 1978
350 400 450 500 550 600 650 700 750 8000
200
400
600
800
1000
1200
1400
1600
1800
Wavelength (nm)
Luminous efficacy (lumens/watt)
Scotopic (rod - dark adjusted)
Photopic (cones - bright light)
Shuman(λ)
Log Human Spectral Sensitivity Function
Vos 1978
350 400 450 500 550 600 650 700 750 800-4
-3
-2
-1
0
1
2
3
4
Wavelength (nm)
Log Luminous efficacy (lumens/watt)
Scotopic (rods - dark adjusted)
Photopic (cones - bright light)
log Shuman(λ)
• Spectral response curves for DSLR with IR-blocksensor filter removed
• Too much IRsensitivity forour application
add partialIR block filterto lens
Camera Spectral Sensitivity
• Spectral response curves for DSLR with IR-blocksensor filter removed& IR lens filter
• Some sensitivityin UV & IRjust outsidevisible
Camera Spectral Sensitivity
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