sensors-15apr10-150dpi-med

sensors-15apr10-150dpi-med - Photons and sensors (with an...

Info iconThis preview shows pages 1–13. Sign up to view the full content.

View Full Document Right Arrow Icon
Photons and sensors (with an interlude on the history of color photography) Marc Levoy Computer Science Department Stanford University CS 178, Spring 2010
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
! Marc Levoy Camera pixel pipeline ! every camera uses different algorithms ! the processing order may vary ! most of it is proprietary 2 sensor processing: demosaicing, white balancing, sharpening, compression analog to digital conversion (ADC) storage
Background image of page 2
! Marc Levoy Canon 21 Mpix CMOS sensor Canon DIGIC 4 processor Example pipeline 3 sensor processing: demosaicing, white balancing, sharpening, compression analog to digital conversion (ADC) storage Compact Flash card
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
! Marc Levoy Canon 21 Mpix CMOS sensor Canon DIGIC 4 processor Example pipeline 4 Compact Flash card
Background image of page 4
! Marc Levoy Outline ! converting photons to charge ! getting the charge off the sensor CCD versus CMOS analog to digital conversion (ADC) ! supporting technology microlenses antialiasing Flters ! sensing color 5
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
! Marc Levoy The photoelectric effect ! when a photon strikes a material, an electron may be emitted depends on the photon’s energy, which depends on its wavelength there is no notion of “brighter photons”, only more or fewer of them 6 Albert Einstein E photon = h ! c " (wikipedia)
Background image of page 6
! Marc Levoy Quantum efFciency ! not all photons will produce an electron depends on quantum efFciency of the device human vision: ~15% typical digital camera: < 50% best back-thinned CCD: > 90% 7 QE = # electrons # photons Hubble Space Telescope Camera 2 back-illuminated CMOS (Sony)
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
! Marc Levoy Pixel size ! the current from one electron is small (10-100 fA) so integrate over space and time (pixel area ! exposure time) larger pixel ! longer exposure means more accurate measure ! typical pixel sizes casio EX-F1: 2.5μ ! 2.5μ = 2 Canon 5D II: 6.4μ ! 6.4μ = 41μ 2 8
Background image of page 8
! Marc Levoy Full well capacity ! how many electrons can a pixel hold? depends mainly on the size of the pixel ! too many photons causes saturation larger capacity leads to higher dynamic range between the brightest scene feature that won’t saturate and the darkest that isn’t too noisy 9 (clarkvision.com)
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
! Marc Levoy Blooming ! charge spilling over to nearby pixels can happen on CCD and CMOS sensors don’t confuse with glare or other image artifacts 10 (ccd-sensor.de)
Background image of page 10
! Marc Levoy Image artifacts can be hard to diagnose 11 Q. Is this blooming? (http://farm3.static.Fickr.com/2102/2248725961_540be5f9af.jpg?v=0)
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
! Marc Levoy Explanation of preceding image (contents of whiteboard) ! there may be blooming in the sky, but the shrinkage of the horse’s leg can be explained purely as a byproduct of misfocus in the accompanying plan view diagram, the horse’s leg is shown at top (in cross section) the solid bundle of rays, corresponding to one sensor pixel, crossed before the leg (was misfocused), then spread out again, but saw only more leg, so its color would be dark
Background image of page 12
Image of page 13
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 52

sensors-15apr10-150dpi-med - Photons and sensors (with an...

This preview shows document pages 1 - 13. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online