surf descriptors - stanford universitysurf – speeded up robust features [bay et al. 2006]! compute...
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Digital Image Processing: Bernd Girod, © 2013 Stanford University -- Image Matching 8
SURF descriptors
n SURF – Speeded Up Robust Features [Bay et al. 2006]!
n Compute horizontal and vertical pixel differences, dx, dy (in local coordinate system for rotation and scale invariance, window size 20σ x 20σ, where σ2 is feature scale)
n Sum dx, dy, and |dx|,|dy| over 4x4 subregions (SURF-64) or 3x3 subregions (SURF-36)"n Normalize vector for gain invariance, but distinguish bright blobs and dark blobs based on sign of
Laplacian (trace of Hessian matrix)"
Digital Image Processing: Bernd Girod, © 2013 Stanford University -- Image Matching 9
DxxDyy-(0.9Dxy)2
Filters"
Dxx
Dxy
Dyy
Blob Response"
Gray"
Computing feature descriptors
Digital Image Processing: Bernd Girod, © 2013 Stanford University -- Image Matching 10
DxxDyy-(0.9Dxy)2
Filters"
Dxx
Dxy
Dyy
Blob Response"
Gray"
Computing feature descriptors
Digital Image Processing: Bernd Girod, © 2013 Stanford University -- Image Matching 11
DxxDyy-(0.9Dxy)2
Filters"
Dxx
Dxy
Dyy
Blob Response"
Gray"
Computing feature descriptors
Digital Image Processing: Bernd Girod, © 2013 Stanford University -- Image Matching 12
Computing feature descriptors
DxxDyy-(0.9Dxy)2
Filters"
Dxx
Dxy
Dyy
Blob Response"
Gray"
Digital Image Processing: Bernd Girod, © 2013 Stanford University -- Image Matching 13
Computing feature descriptors
Maxima"
x"
y"
Digital Image Processing: Bernd Girod, © 2013 Stanford University -- Image Matching 14
Computing feature descriptors
Gradient Field for Oriented Patch"
Orient Along "Dominant Gradient"
Digital Image Processing: Bernd Girod, © 2013 Stanford University -- Image Matching 15
Computing feature descriptors SU
RF
Des
crip
tor"
Σ dx Σ dy Σ|dx| Σ|dy|
Σ dx Σ dy Σ|dx| Σ|dy|
Σ dx Σ dy Σ|dx| Σ|dy|
SIFT
Des
crip
tor"
Σ Σ Σ Σ Σ Σ Σ Σ
dx
dy
…"
…"