front-end computations in human vision
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Front-end computations in human vision
Jitendra MalikU.C. Berkeley
References: DeValois & DeValois,Hubel, Palmer, Spillman &Werner, Wandell
Cerebral Cortex
Monocular Visual Field: 160 deg (w) X 135 deg (h)Binocular Visual Field: 200 deg (w) X 135 deg (h)
Cones and Rods
ON and OFF cells in retinal ganglia
Modeling simple cells
• Elongated directional Gaussian derivatives
• 2nd derivative and Hilbert transform
• L1 normalized for scale invariance
• 6 orientations, 3 scales• Zero mean
Orientation Energy
• Gaussian 2nd derivative and its Hilbert pair
•
• Can detect combination of bar and edge features; also insensitive to linear shading [Perona&Malik 90]
• Multiple scales
22 )()( evenodd fIfIOE
Visual Processing Areas
Macaque Visual Areas
Textons (Malik et al, IJCV 2001)• K-means on vectors of filter responses
Textons (cont.)
Texton Histograms
i
j
k
K
m ji
jiji mhmh
mhmhhh
1
22
)()()]()([
21),(Chi square test:
0.1
0.8
CSF as function of eccentricity
Receptor density vs eccentricity
Cortical Magnification Factor
Mapping from Retina to V1
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