Transcript
Page 1: Dark Flash Photography

Dark Flash Photography

Dilip KrishnanRob 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 LevelsWant 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

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• Dark flash is ~200 times dimmer than conventional Ground truthReconstruction2. Ambient image

Dark Flash Photography

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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Digital Camera Sensor

Two Sensors

The Human Retina

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Human Retina Spectral Sensitivity

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Human Retina Sensitivity – Log Scale

Note:Steep falloff outside400-700nm

range

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Digital Camera Sensor

Two Sensors

The Human Retina

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Camera Spectral Sensitivity

• Spectral response curves for an unmodified DSLR

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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

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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

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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 TLV

tables 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

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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)

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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)

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• Spectral response curves for DSLR with IR-blocksensor filter removed

• Too much IRsensitivity forour application

add partialIR block filterto lens

Camera Spectral Sensitivity

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• 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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