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Dark Flash Photography

Dark Flash Photography. Dilip Krishnan Rob Fergus Dept. of Computer Science Courant 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:.

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Dark Flash Photography

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  1. Dark Flash Photography Dilip Krishnan Rob Fergus Dept. of Computer ScienceCourant Institute, New York University

  2. Taking Photos in Low Light Levels Taking Photos in Low Light Levels

  3. Taking Photos in Low Light Levels Want to avoid sensor noise & camera shake Possible solutions: • Large Aperture Lens • Expensive, Depth-of Field issues • 2. Image stabilization • Only gives a few extra stops of exposure • 3. Camera flash • Active method, • Disturbs Scene Drawbacks: Can be used in conjunctionwith our approach Our paper addresses these issues

  4. Dark Flash Photography • Dark flash is ~200 times dimmer than conventional 1. Dark Flash image 2. Ambient image Reconstruction Ground truth

  5. Key Challenges • How to add light to the scene without it being perceived by people. • How to obtain an image to true colors.

  6. Two Sensors The Human Retina Digital Camera Sensor

  7. Human Retina Spectral Sensitivity

  8. Human Retina Sensitivity – Log Scale Note:Steep fall off outside400-700nmrange

  9. Two Sensors The Human Retina Digital Camera Sensor

  10. Camera Spectral Sensitivity • Spectral response curves for an unmodified DSLR

  11. Camera Spectral Sensitivity Modify camera by: 1. Remove IR-blocksensor filter 2. Adding lensfilter to remove IR >800nm  Some sensitivityin UV & IR just outside visible

  12. Camera Spectral Sensitivity • Comparison with human sensitivity curve • Camera’s response is significantly broader • Possible to addlight without being easy perceived Human Response Curve (not to scale)

  13. Dark Flash Emission Spectrum CameraSpectralSensitivity Dark FlashEmission

  14. Demonstration of Dark Flash • Please look directly at the demonstration,NOT at the projection screens

  15. Comparison to Visible Flash • Both flashes will fire simultaneously • Both give comparable camera exposure • Dark flash is ~220x dimmer than visible flash

  16. 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 Hazard Factor Dark Light @ 1m for ~1 sec

  17. Luminous efficacy (lumens/watt) 1800 1600 Scotopic (rod - dark adjusted) 1400 Photopic (cones - bright light) 1200 1000 800 600 400 200 0 350 400 450 500 550 600 650 700 750 800 Wavelength (nm) Human Spectral Sensitivity Function Shuman(λ) Vos 1978

  18. Log Luminous efficacy (lumens/watt) 4 3 2 1 0 -1 Scotopic (rods - dark adjusted) -2 Photopic (cones - bright light) -3 -4 350 400 450 500 550 600 650 700 750 800 Wavelength (nm) Log Human Spectral Sensitivity Function log Shuman(λ) Vos 1978

  19. Camera Spectral Sensitivity • Spectral response curves for DSLR with IR-blocksensor filter removed • Too much IRsensitivity forour application add partialIR block filterto lens

  20. 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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