front-end computations in human vision jitendra malik u.c. berkeley references: devalois &...
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Front-end computations in human vision
Front-end computations in human vision
Jitendra MalikU.C. Berkeley
References: DeValois & DeValois,Hubel, Palmer, Spillman &Werner, Wandell
Jitendra MalikU.C. Berkeley
References: DeValois & DeValois,Hubel, Palmer, Spillman &Werner, Wandell
Cerebral CortexCerebral Cortex
Monocular Visual Field: 160 deg (w) X 135 deg (h)Binocular Visual Field: 200 deg (w) X 135 deg (h)Monocular Visual Field: 160 deg (w) X 135 deg (h)Binocular Visual Field: 200 deg (w) X 135 deg (h)
Cones and RodsCones and Rods
ON and OFF cells in retinal gangliaON and OFF cells in retinal ganglia
Modeling simple cellsModeling simple cells
• Elongated directional Gaussian derivatives
• 2nd derivative and Hilbert transform
• L1 normalized for scale invariance
• 6 orientations, 3 scales• Zero mean
• Elongated directional Gaussian derivatives
• 2nd derivative and Hilbert transform
• L1 normalized for scale invariance
• 6 orientations, 3 scales• Zero mean
Orientation EnergyOrientation 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 AreasVisual Processing Areas
Macaque Visual AreasMacaque Visual Areas
Textons (Malik et al, IJCV 2001)Textons (Malik et al, IJCV 2001)• K-means on vectors of filter responses• K-means on vectors of filter responses
Textons (cont.)Textons (cont.)
Texton HistogramsTexton Histograms
i
j
k
K
m ji
jiji mhmh
mhmhhh
1
22
)()(
)]()([
2
1),(Chi square test:
0.1
0.8
CSF as function of eccentricityCSF as function of eccentricity
Receptor density vs eccentricityReceptor density vs eccentricity
Cortical Magnification FactorCortical Magnification Factor
Mapping from Retina to V1Mapping from Retina to V1