InterestPoints.h

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// -*- c-basic-offset: 4 -*-

#ifndef VIGRA_EXT_INTEREST_POINTS
#define VIGRA_EXT_INTEREST_POINTS

#include <vector>
#include <map>

#include <vigra/error.hxx>
#include <vigra/impex.hxx>
#include <vigra/cornerdetection.hxx>
#include <vigra/localminmax.hxx>
#include <vigra/diff2d.hxx>

namespace vigra_ext
{

template <class ImageIter, class ImageAcc>
void findInterestPointsPartial(vigra::triple<ImageIter, ImageIter, ImageAcc> img, const vigra::Rect2D& rect, double scale,
    unsigned nPoints, std::multimap<double, vigra::Diff2D> &points
    )
{
    // find interesting corners using harris corner detector
    // working only in given rectangle

    // select the nPoints with the highest response
    // some distribution criteria might be useful, too
    // to avoid clustering all points on a single object.
    vigra::BImage leftCorners(rect.size(), vigra::UInt8(0));
    vigra::FImage leftCornerResponse(rect.size());

    DEBUG_DEBUG("running corner detector. nPoints: " << nPoints << ",  scale: " << scale);
    // find corner response at scale scale
    vigra::cornerResponseFunction(srcIterRange(img.first + rect.upperLeft(), img.first + rect.lowerRight(), img.third),
        vigra::destImage(leftCornerResponse), scale);

    // find local maxima of corner response, mark with 1
    vigra::localMaxima(vigra::srcImageRange(leftCornerResponse), vigra::destImage(leftCorners), 255);

    double minResponse = 0;
    points.clear();
    // sample grid on img1 and try to add ctrl points
    for (int y = 0; y < rect.height(); y++)
    {
        for (int x = 0; x < rect.width(); x++)
        {
            if (leftCorners(x, y) == 0)
            {
                continue;
            }
            double resp = leftCornerResponse(x, y);
            if (resp > minResponse)
            {
                // add to point map
                points.insert(std::make_pair(resp, vigra::Diff2D(x, y) + rect.upperLeft()));
                // if we have reached the maximum
                // number of points, increase the threshold, to avoid
                // growing the points map too much.
                // extract more than nPoints, because some might be bad
                // and cannot be matched with the other image.
                if (points.size() > nPoints)
                {
                    // remove the point with the lowest corner response.
                    points.erase(points.begin());
                    // use new threshold for next selection.
                    minResponse = points.begin()->first;
                }
            }
        }
    }
}

} // namespace

#endif