vigra - Symmetry Detection

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| Symmetry Detection |

## Functions
template<... >
void | radialSymmetryTransform (...)
| Find centers of radial symmetry in an image. More...

## Detailed Description

Measure the local symmetry at each pixel.

## Function Documentation

void vigra::radialSymmetryTransform | ( |  | ... | ) |

Find centers of radial symmetry in an image.

This algorithm implements the Fast Radial Symmetry Transform according to [G. Loy, A. Zelinsky: "A Fast Radial Symmetry Transform for Detecting Points of Interest", in: A. Heyden et al. (Eds.): Proc. of 7th European Conf. on Computer Vision, Part 1, pp. 358-368, Springer LNCS 2350, 2002]. Minima of the algorithm response mark dark blobs, maxima correspond to light blobs. The "radial strictness parameter" is fixed at `alpha` = 2.0, the spatial spreading of the raw response is done by a Gaussian convolution at `0.25*scale` (these values are recommendations from the paper). Loy and Zelinsky additionally propose to add the operator response from several scales (see usage example below).

Declarations:

pass 2D array views:

namespace vigra {
template <class T1, class S1,
class T2, class S2>
void
radialSymmetryTransform(MultiArrayView<2, T1, S1> const & src,
MultiArrayView<2, T2, S2> dest,
double scale);
}

show deprecated declarations

pass Image Iterators and Data Accessors :
namespace vigra {
template <class SrcIterator, class SrcAccessor,
class DestIterator, class DestAccessor>
void
radialSymmetryTransform(SrcIterator sul, SrcIterator slr, SrcAccessor as,
DestIterator dul, DestAccessor ad,
double scale)
}

use argument objects in conjunction with Argument Object Factories :

namespace vigra {
template <class SrcIterator, class SrcAccessor,
class DestIterator, class DestAccessor>
inline
void radialSymmetryTransform(
triple<SrcIterator, SrcIterator, SrcAccessor> src,
pair<DestIterator, DestAccessor> dest,
double scale)
}

Usage:

#include <vigra/symmetry.hxx>
Namespace: vigra

MultiArray<2, unsigned char> src(w,h), centers(w,h);
MultiArray<2, float> symmetry(w,h);
// use edge detection filters at various scales
for(double scale = 2.0; scale <= 8.0; scale *= 2.0)
{
MultiArray<2, float> tmp(w,h);
// find centers of symmetry
radialSymmetryTransform(src, tmp, scale);
symmetry += tmp;
}
// mark centers of symmetry
centers.init(128);
localMinima(symmetry, centers, 0);
localMaxima(symmetry, centers, 255);

show deprecated examples

vigra::BImage src(w,h), centers(w,h);
vigra::FImage symmetry(w,h);
// empty result image
centers.init(128);
symmetry.init(0.0);
// input width of edge detection filter
for(double scale = 2.0; scale <= 8.0; scale *= 2.0)
{
vigra::FImage tmp(w,h);
// find centers of symmetry
radialSymmetryTransform(srcImageRange(src), destImage(tmp), scale);
combineTwoImages(srcImageRange(symmetry), srcImage(tmp), destImage(symmetry),
std::plus<float>());
}
localMinima(srcImageRange(symmetry), destImage(centers), 0);
localMaxima(srcImageRange(symmetry), destImage(centers), 255);

Required Interface:

SrcImageIterator src_upperleft, src_lowerright;
DestImageIterator dest_upperleft;
SrcAccessor src_accessor;
DestAccessor dest_accessor;
// SrcAccessor::value_type must be a built-in type
SrcAccessor::value_type u = src_accessor(src_upperleft);
dest_accessor.set(u, dest_upperleft);

© Ullrich Köthe (ullrich.koethe@iwr.uni-heidelberg.de) Heidelberg Collaboratory for Image Processing, University of Heidelberg, Germany | html generated using doxygen and Python vigra 1.10.0 (Mon Nov 18 2013)