dlibs/dlib/image_keypoint/surf.h

// Copyright (C) 2009  Davis E. King ([email protected])
// License: Boost Software License   See LICENSE.txt for the full license.
#ifndef DLIB_SURf_H_
#define DLIB_SURf_H_

#include "surf_abstract.h"
#include "hessian_pyramid.h"
#include "../matrix.h"

namespace dlib
{

// ----------------------------------------------------------------------------------------
    
    struct surf_point
    {
        interest_point p;
        matrix<double,64,1> des;
        double angle;
    };

// ----------------------------------------------------------------------------------------

    inline void serialize(
        const surf_point& item,  
        std::ostream& out
    )
    {
        try
        {
            serialize(item.p,out);
            serialize(item.des,out);
            serialize(item.angle,out);
        }
        catch (serialization_error& e)
        { 
            throw serialization_error(e.info + "\n   while serializing object of type surf_point"); 
        }
    }

// ----------------------------------------------------------------------------------------

    inline void deserialize(
        surf_point& item,  
        std::istream& in 
    )
    {
        try
        {
            deserialize(item.p,in);
            deserialize(item.des,in);
            deserialize(item.angle,in);
        }
        catch (serialization_error& e)
        { 
            throw serialization_error(e.info + "\n   while deserializing object of type surf_point"); 
        }
    }

// ----------------------------------------------------------------------------------------

    inline double gaussian (double x, double y, double sig)
    {
        DLIB_ASSERT(sig > 0,
            "\tdouble gaussian()"
            << "\n\t sig must be bigger than 0"
            << "\n\t sig: " << sig 
        );
        const double sqrt_2_pi = 2.5066282746310002416123552393401041626930;
        return 1.0/(sig*sqrt_2_pi) * std::exp( -(x*x + y*y)/(2*sig*sig));
    }

// ----------------------------------------------------------------------------------------

    template <typename integral_image_type, typename T>
    double compute_dominant_angle (
        const integral_image_type& img,
        const dlib::vector<T,2>& center,
        const double& scale
    )
    {
        DLIB_ASSERT(get_rect(img).contains(centered_rect(center, (unsigned long)(17*scale),(unsigned long)(17*scale))) == true &&
                    scale > 0,
            "\tdouble compute_dominant_angle(img, center, scale)"
            << "\n\tAll arguments to this function must be > 0"
            << "\n\t get_rect(img): " << get_rect(img) 
            << "\n\t center:        " << center 
            << "\n\t scale:         " << scale 
        );


        std::vector<double> ang;
        std::vector<dlib::vector<double,2> > samples;

        const long sc = static_cast<long>(scale+0.5);

        // accumulate a bunch of angle and vector samples
        dlib::vector<double,2> vect;
        for (long r = -6; r <= 6; ++r)
        {
            for (long c = -6; c <= 6; ++c)
            {
                if (r*r + c*c < 36)
                {
                    // compute a Gaussian weighted gradient and the gradient's angle.
                    const double gauss = gaussian(c,r, 2.5);
                    vect.x() = gauss*haar_x(img, sc*point(c,r)+center, 4*sc);
                    vect.y() = gauss*haar_y(img, sc*point(c,r)+center, 4*sc);
                    samples.push_back(vect);
                    ang.push_back(atan2(vect.y(), vect.x()));
                }
            }
        }


        // now find the dominant direction
        double max_length = 0;
        double best_ang = 0;
        // look at a bunch of pie shaped slices of a circle 
        const long slices = 45;
        const double ang_step = (2*pi)/slices;
        for (long ang_i = 0; ang_i < slices; ++ang_i)
        {
            // compute the bounding angles
            double ang1 = ang_step*ang_i - pi;
            double ang2 = ang1 + pi/3;


            // compute sum of all vectors that are within the above two angles
            vect.x() = 0;
            vect.y() = 0;
            for (unsigned long i = 0; i < ang.size(); ++i)
            {
                if (ang1 <= ang[i] && ang[i] <= ang2)
                {
                    vect += samples[i];
                }
                else if (ang2 > pi && (ang[i] >= ang1 || ang[i] <= (-2*pi+ang2)))
                {
                    vect += samples[i];
                }
            }


            // record the angle of the best vectors
            if (length_squared(vect) > max_length)
            {
                max_length = length_squared(vect);
                best_ang = atan2(vect.y(), vect.x());
            }
        }

        return best_ang;
    }

// ----------------------------------------------------------------------------------------

    template <typename integral_image_type, typename T, typename MM, typename L>
    void compute_surf_descriptor (
        const integral_image_type& img,
        const dlib::vector<T,2>& center,
        const double scale,
        const double angle,
        matrix<double,64,1,MM,L>& des
    )
    {
        DLIB_ASSERT(get_rect(img).contains(centered_rect(center, (unsigned long)(32*scale),(unsigned long)(32*scale))) == true &&
                    scale > 0,
            "\tvoid compute_surf_descriptor(img, center, scale, angle)"
            << "\n\tAll arguments to this function must be > 0"
            << "\n\t get_rect(img): " << get_rect(img) 
            << "\n\t center:        " << center 
            << "\n\t scale:         " << scale 
        );

        point_rotator rot(angle);
        point_rotator inv_rot(-angle);

        const long sc = static_cast<long>(scale+0.5);
        long count = 0;

        // loop over the 4x4 grid of histogram buckets 
        for (long r = -10; r < 10; r += 5)
        {
            for (long c = -10; c < 10; c += 5)
            {
                dlib::vector<double,2> vect, abs_vect, temp;

                // 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)
                {
                    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); 

                        // 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);

                        vect += temp;
                        abs_vect += abs(temp);
                    }
                }

                des(count++) = vect.x();
                des(count++) = vect.y();
                des(count++) = abs_vect.x();
                des(count++) = abs_vect.y();
            }
        }

        // Return the length normalized descriptor.  Add a small number
        // to guard against division by zero.
        const double len = length(des) + 1e-7;
        des = des/len;
    }

// ----------------------------------------------------------------------------------------

    template <typename image_type>
    const std::vector<surf_point> get_surf_points (
        const image_type& img,
        long max_points = 10000,
        double detection_threshold = 30.0
    )
    {
        DLIB_ASSERT(max_points > 0 && detection_threshold >= 0,
            "\t std::vector<surf_point> get_surf_points()"
            << "\n\t Invalid arguments were given to this function."
            << "\n\t max_points:          " << max_points 
            << "\n\t detection_threshold: " << detection_threshold 
        );

        // Figure out the proper scalar type we should use to work with these pixels.  
        typedef typename pixel_traits<typename image_traits<image_type>::pixel_type>::basic_pixel_type bp_type;
        typedef typename promote<bp_type>::type working_pixel_type;

        // make an integral image first
        integral_image_generic<working_pixel_type> int_img;
        int_img.load(img);

        // now make a hessian pyramid
        hessian_pyramid pyr;
        pyr.build_pyramid(int_img, 4, 6, 2);

        // now get all the interest points from the hessian pyramid
        std::vector<interest_point> points; 
        get_interest_points(pyr, detection_threshold, points);
        std::vector<surf_point> spoints;

        // sort all the points by how strong their detect is
        std::sort(points.rbegin(), points.rend());

        // now extract SURF descriptors for the points
        surf_point sp;
        for (unsigned long i = 0; i < std::min((size_t)max_points,points.size()); ++i)
        {
            // ignore points that are close to the edge of the image
            const double border = 32;
            const unsigned long border_size = static_cast<unsigned long>(border*points[i].scale);
            if (get_rect(int_img).contains(centered_rect(points[i].center, border_size, border_size)))
            {
                sp.angle = compute_dominant_angle(int_img, points[i].center, points[i].scale);
                compute_surf_descriptor(int_img, points[i].center, points[i].scale, sp.angle, sp.des);
                sp.p = points[i];

                spoints.push_back(sp);
            }
        }

        return spoints;
    }

// ----------------------------------------------------------------------------------------

}

#endif // DLIB_SURf_H_