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SUMMARY:What is a flutter shutter good for? - Jean-Michel Morel (ENS Cacha
 n)
DTSTART:20130425T140000Z
DTEND:20130425T150000Z
UID:TALK39487@talks.cam.ac.uk
CONTACT:Carola-Bibiane Schoenlieb
DESCRIPTION:Until recently moving objects could only be photographed with 
 short exposure times\, to avoid motion blur.\nYet\, recently two groundbre
 aking works in computational photography offer new  camera designs  allowi
 ng arbitrary exposure times. The "flutter shutter" of Agrawal et al. creat
 es an invertible motion blur by using a clever shutter technique to interr
 upt the photon flux during the exposure time according to a well chosen bi
 nary sequence. The "motion-invariant photography" of Levin et al. gets the
  same result by a uniformly accelerated camera motion.  \nThis talk propos
 es a simple mathematical method for evaluating the image quality of these 
 new cameras. The theory\, providing explicit formulas for the SNR obtained
  after deconvolution\, raises a central paradox for these cameras: It show
 s that even an infinite exposure time cannot bring an SNR increase of more
  than 17%! \n Nevertheless\, three consequences of the theory permit to mi
 tigate this harsh limitation. First\, this SNR gain can be obtained on any
  video with moderate motion blur by a very simple new video temporal filte
 r.  The video  improvement by this blind deconvolution is visible. Second\
 , we show that if a probabilistic motion model is available\, then one can
  compute an optimal flutter shutter with SNR exceeding significantly the p
 redicted limit. Third\, we show that the "best snapshot'' for a given expo
 sure time is not obtained with a  constant aperture: it is obtained with a
  flutter shutter. \n\nThis is joint work with Yohann Tendero
LOCATION:MR 14\, CMS
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