dlib/examples/surf_ex.cpp

// The contents of this file are in the public domain. See LICENSE_FOR_EXAMPLE_PROGRAMS.txt
/*

    This is a simple example illustrating the use of the get_surf_points()
    function.  It pulls out the first 100 SURF points from an input image 
    and displays them on the screen as an overlay on the image.

    For a description of the SURF algorithm you should consult the following
    papers:
        This is the original paper which introduced the algorithm:
            SURF: Speeded Up Robust Features
            By Herbert Bay, Tinne Tuytelaars, and Luc Van Gool

        This paper provides a nice detailed overview of how the algorithm works:
            Notes on the OpenSURF Library by Christopher Evans

*/



#include "dlib/gui_widgets.h"
#include "dlib/image_io.h"
#include "dlib/image_keypoint.h"
#include <fstream>


using namespace std;
using namespace dlib;

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

int main(int argc, char** argv)
{
    try
    {
        // make sure the user entered an argument to this program
        if (argc != 2)
        {
            cout << "error, you have to enter a BMP file as an argument to this program" << endl;
            return 1;
        }

        // Here we open the image file.  Note that when you open a binary file with 
        // the C++ ifstream you must supply the ios::binary flag.
        ifstream fin(argv[1],ios::binary);
        if (!fin)
        {
            cout << "error, can't find " << argv[1] << endl;
            return 1;
        }

        // Here we declare an image object that can store rgb_pixels.  Note that in 
        // dlib there is no explicit image object, just a 2D array and
        // various pixel types.  
        array2d<rgb_pixel>::kernel_1a img;

        // now load the bmp file into our image.  If the file isn't really a BMP
        // or is corrupted then load_bmp() will throw an exception.
        load_bmp(img, fin);

        // get the 100 strongest SURF points from the image
        std::vector<surf_point> sp = get_surf_points(img, 100);

        // create a window to display the input image and the SURF boxes
        image_window my_window(img);

        // Now lets draw some rectangles on top of the image so we can see where
        // SURF found its points.
        for (unsigned long i = 0; i < sp.size(); ++i)
        {
            // Pull out the info from the SURF point relevant to figuring out
            // where its rotated box should be.
            const unsigned long box_size = static_cast<unsigned long>(sp[i].p.scale*20);
            const double ang = sp[i].angle;
            const point center(sp[i].p.center);
            rectangle rect = centered_rect(center, box_size, box_size); 

            // Rotate the 4 corners of the rectangle 
            const point p1 = rotate_point(center, rect.tl_corner(), ang);
            const point p2 = rotate_point(center, rect.tr_corner(), ang);
            const point p3 = rotate_point(center, rect.bl_corner(), ang);
            const point p4 = rotate_point(center, rect.br_corner(), ang);

            // Draw the sides of the box as red lines
            my_window.add_overlay(image_window::overlay_line(p1, p2, rgb_pixel(255,0,0)));
            my_window.add_overlay(image_window::overlay_line(p1, p3, rgb_pixel(255,0,0)));
            my_window.add_overlay(image_window::overlay_line(p4, p2, rgb_pixel(255,0,0)));
            my_window.add_overlay(image_window::overlay_line(p4, p3, rgb_pixel(255,0,0)));

            // Draw a line from the center to the top side so we can see how the box is oriented.
            // Also make this line green.
            my_window.add_overlay(image_window::overlay_line(center, (p1+p2)/2, rgb_pixel(0,255,0)));
        }

        // wait until the user closes the window before we let the program 
        // terminate.
        my_window.wait_until_closed();
    }
    catch (exception& e)
    {
        cout << "exception thrown: " << e.what() << endl;
    }
}

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