Transcript CS332 Visual Processing - Computer Science

Early Processing in Biological Vision
Analyzing intensity changes
in the retinal image
CS332 Visual Processing
Department of Computer Science
Wellesley College
The human eye
CS332 Visual Processing
Department of Computer Science
Wellesley College
The structure of a neuron
Major parts of a neuron:
1) dendrites
2) cell body
3) axon
4) terminals and synapses
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1011 neurons in the brain
1-3
Projection from the retina
1st cortical stage of
visual processing:
primary visual cortex
(or area V1)
1-4
Retinal ganglion cells
receptive fields exhibit a center-surround structure,
whose cross-section is the difference of two Gaussians
1-5
Processing within the retina
1-6
Analyzing a 2D image
image
image after
smoothing and
second derivative
black =
negative
zero-crossings
white =
positive
1-7
Mapping cortical receptive fields
David Hubel & Torston Wiesel
1-8
Single-cell recording from visual cortex
Hubel & Wiesel identified 3 basic cell types:
simple, complex, hypercomplex cells
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Some simple cells respond best to lines…
B. Dark Line Detector
Firing
Rate
Horizontal Position
… of a particular contrast sign, orientation, position
1-10
Some simple cells respond best to edges
C. Dark-to-light Edge Detector
Firing
Rate
D. Light-to-dark Edge Detector
Firing
Rate
Horizontal Position
Horizontal Position
Again, of a particular contrast sign, orientation, position
large receptive fields  coarse spatial structure
small receptive fields  fine spatial structure
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Detection of luminance edges
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Simple cells appear to
detect edges and lines
Many complex cells are
also selective for stereo
disparity and motion
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