front-end computations in human vision jitendra malik u.c. berkeley references: devalois &...

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