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);