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Added a non-uniform weighting to each SURF bin. This improves 

the mean average precision when matching SURF descriptors
by about 2%.
This commit is contained in:
Davis King 2013-02-18 17:37:49 -05:00
parent f52f4522b1
commit bba96f36b5
1 changed files with 18 additions and 5 deletions
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23
dlib/image_keypoint/surf.h
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@ -187,16 +187,29 @@ namespace dlib
{
dlib::vector<double,2> vect, abs_vect, temp;
// now loop over 25 points in this bucket and sum their features
for (long y = r; y < r+5; ++y)
// now loop over 25 points in this bucket and sum their features. Note
// that we include 1 pixels worth of padding around the outside of each 5x5
// cell. This is to help neighboring cells interpolate their counts into
// each other a little bit.
for (long y = r-1; y < r+5+1; ++y)
{
for (long x = c; x < c+5; ++x)
if (y < -10 || y >= 10)
continue;
for (long x = c-1; x < c+5+1; ++x)
{
if (x < -10 || x >= 10)
continue;
// get the rotated point for this extraction point
point p(rot(point(x,y)*scale) + center);
temp.x() = haar_x(img, p, 2*sc);
temp.y() = haar_y(img, p, 2*sc);
// Give points farther from the center of the bucket a lower weight.
const long center_r = r+2;
const long center_c = c+2;
const double weight = 1.0/(4+std::abs(center_r-y) + std::abs(center_c-x));
temp.x() = weight*haar_x(img, p, 2*sc);
temp.y() = weight*haar_y(img, p, 2*sc);
// rotate this vector into alignment with the surf descriptor box
temp = inv_rot(temp);