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SUMMARY:What reflected light tells the eye about the content of the world 
 - Prof. David H. Foster\, School of Electrical and Electronic Engineering\
 , University of Manchester
DTSTART:20090330T120000Z
DTEND:20090330T130000Z
UID:TALK16911@talks.cam.ac.uk
CONTACT:John Mollon
DESCRIPTION:The spectrum of the light from a scene depends on its reflecti
 ng properties. Differences in reflectances allow surfaces to be discrimina
 ted and\, potentially\, uniquely identified. But inferences about the cont
 ent of a scene cannot be made directly from the reflected light. This is b
 ecause reflected spectra from the same surfaces change with changes in sce
 ne illumination\; and\, conversely\, under the same illumination\, reflect
 ed spectra from different surfaces can produce the same responses in the r
 eceptors of the eye. In short\, there is no one-to-one correspondence betw
 een surfaces and receptoral activity. Given these uncertainties\, what are
  the physical limits on an observer’s ability to identify surfaces\, esp
 ecially in natural scenes? The aim here is to estimate how much informatio
 n in a scene is actually available to an ideal trichromatic observer\; how
  efficiently this information is coded at receptoral and post-receptoral l
 evels\; and how efficiently it can be retrieved in practice in a simple ta
 sk requiring point-by-point identification across images of a scene. It is
  shown that coding at receptoral levels is highly redundant\, but postrece
 ptorally\, its efficiency increases markedly\, by about an order of magnit
 ude. Critically\, a postreceptoral transformation providing minimum redund
 ancy in the information available yields the maximum information retrievab
 le in identification. 
LOCATION:Kenneth Craik Room\, Craik-Marshall Building\, Downing Site
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