dlib/examples/object_detector_ex.cpp

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

    This is an example illustrating the use of the dlib tools for
    detecting objects in images.  In this example we will create
    three simple images, each containing some white squares.  We
    will then use the sliding window classifier tools to learn to 
    detect these squares.

*/


#include "dlib/svm_threaded.h"
#include "dlib/gui_widgets.h"
#include "dlib/array.h"
#include "dlib/array2d.h"
#include "dlib/image_keypoint.h"
#include "dlib/image_processing.h"

#include <iostream>
#include <fstream>


using namespace std;
using namespace dlib;

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

template <
    typename image_array_type
    >
void make_simple_test_data (
    image_array_type& images,
    std::vector<std::vector<rectangle> >& object_locations
)
/*!
    ensures
        - #images.size() == 3
        - #object_locations.size() == 3
        - Creates some simple images to test the object detection routines.  In particular, 
          this function creates images with white 70x70 squares in them.  It also stores 
          the locations of these squares in object_locations.  
        - for all valid i:
            - object_locations[i] == A list of all the white rectangles present in images[i].
!*/
{
    images.clear();
    object_locations.clear();

    images.resize(3);
    images[0].set_size(400,400);
    images[1].set_size(400,400);
    images[2].set_size(400,400);

    // set all the pixel values to black
    assign_all_pixels(images[0], 0);
    assign_all_pixels(images[1], 0);
    assign_all_pixels(images[2], 0);

    // Now make some squares and draw them onto our black images. All the
    // squares will be 70 pixels wide and tall.

    std::vector<rectangle> temp;
    temp.push_back(centered_rect(point(100,100), 70,70)); 
    fill_rect(images[0],temp.back(),255); // Paint the square white
    temp.push_back(centered_rect(point(200,300), 70,70));
    fill_rect(images[0],temp.back(),255); // Paint the square white
    object_locations.push_back(temp);

    temp.clear();
    temp.push_back(centered_rect(point(140,200), 70,70));
    fill_rect(images[1],temp.back(),255); // Paint the square white
    temp.push_back(centered_rect(point(303,200), 70,70));
    fill_rect(images[1],temp.back(),255); // Paint the square white
    object_locations.push_back(temp);

    temp.clear();
    temp.push_back(centered_rect(point(123,121), 70,70));
    fill_rect(images[2],temp.back(),255); // Paint the square white
    object_locations.push_back(temp);
}

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

int main()
{  
    try
    {
        // The first thing we do is create the set of 3 images discussed above.  
        typedef array<array2d<unsigned char> >::expand_1b  grayscale_image_array_type;
        grayscale_image_array_type images;
        std::vector<std::vector<rectangle> > object_locations;
        make_simple_test_data(images, object_locations);


        /*
            This next block of code specifies the type of sliding window classifier we will
            be using to detect the white squares.  The most important thing here is the
            scan_image_pyramid template.  Instances of this template represent the core
            of a sliding window classifier.  To go into more detail, the sliding window 
            classifiers used by this object have three parts: 
                   1. The underlying feature extraction.  See the dlib documentation for a detailed 
                      discussion of how the hashed_feature_image and hog_image feature extractors
                      work.  However, to understand this example, all you need to know is that the 
                      feature extractor associates a vector with each location in an image.  This 
                      vector is supposed to capture information which describes how parts of the 
                      image look in a way that is relevant to the problem you are trying to solve.

                   2. A detection template.  This is a rectangle which defines the shape of a 
                      sliding window (the object_box), as well as a set of rectangles which
                      envelop it.  This set of enveloping rectangles defines the spatial
                      structure of the overall feature extraction within a sliding window.  
                      In particular, each location of a sliding window has a feature vector
                      associated with it.  This feature vector is defined as follows:
                        - Let N denote the number of enveloping rectangles.
                        - Let M denote the dimensionality of the vectors output by feature_extractor_type
                          objects.
                        - Let F(i) == the M dimensional vector which is the sum of all vectors 
                          given by our feature_extractor_type object inside the ith enveloping 
                          rectangle.
                        - Then the feature vector for a sliding window is an M*N dimensional vector
                          [F(1) F(2) F(3) ... F(N)] (i.e. it is a concatenation of the N vectors).
                          This feature vector can be thought of as a collection of N "bags of features",
                          each bag coming from a spatial location determined by one of the enveloping 
                          rectangles. 
                          
                   3. A weight vector and a threshold value.  The dot product between the weight
                      vector and the feature vector for a sliding window location gives the score 
                      of the window.  If this score is greater than the threshold value then the 
                      window location is output as a detection.  You don't need to determine these
                      parameters yourself.  They are automatically populated by the 
                      structural_object_detection_trainer.

                Finally, the sliding window classifiers described above are applied to every level 
                of an image pyramid.   So you need to tell scan_image_pyramid what kind of pyramid
                you want to use.  In this case we are using pyramid_down which downsamples each
                pyramid layer by half (dlib also contains other version of pyramid_down which result 
                in finer grained pyramids).
        */
        typedef hashed_feature_image<hog_image<3,3,1,4,hog_signed_gradient,hog_full_interpolation> > feature_extractor_type;
        typedef scan_image_pyramid<pyramid_down, feature_extractor_type> image_scanner_type;
        image_scanner_type scanner;
        // Setup the sliding window box.  Lets use a window with the same shape as the white boxes we
        // are trying to detect.
        const rectangle object_box = compute_box_dimensions(1,    // width/height ratio
                                                            70*70 // box area 
                                                            );
        // Setup the detection template so it contains 4 feature extraction zones inside the object_box.  These
        // are the upper left, upper right, lower left, and lower right quadrants of object_box.  (Note that
        // in general we can add more than one detection template.  But in this case one is enough.)
        scanner.add_detection_template(object_box, create_grid_detection_template(object_box,2,2));





        // Now that we have defined the kind of sliding window classifier system we want and stored 
        // the details into the scanner object we are ready to use the structural_object_detection_trainer
        // to learn the weight vector and threshold needed to produce a complete object detector.
        structural_object_detection_trainer<image_scanner_type> trainer(scanner);
        trainer.set_num_threads(4); // Set this to the number of processing cores on your machine. 

        // This line tells the algorithm that it is never OK for two detections to overlap.  So
        // this controls how the non-max suppression is performed and in general you can set this up
        // any way you like. 
        trainer.set_overlap_tester(test_box_overlap(0));

        // There are a variety of other useful parameters to the structural_object_detection_trainer.  
        // Examples of the ones you are most likely to use follow (see dlib documentation for what they do):
        //trainer.set_overlap_eps(0.80);
        //trainer.set_c(1.0);
        //trainer.set_loss_per_missed_target(1);
        //trainer.set_loss_per_false_alarm(1);


        // Do the actual training and save the results into the detector object.  
        object_detector<image_scanner_type> detector = trainer.train(images, object_locations);

        // We can easily test the new detector against our training data.  This print statement will indicate that it
        // has perfect precision and recall on this simple task.
        cout << "Test detector (precision,recall): " << test_object_detection_function(detector, images, object_locations) << endl;

        // The cross validation should also indicate perfect precision and recall.
        cout << "3-fold cross validation (precision,recall): "
             << cross_validate_object_detection_trainer(trainer, images, object_locations, 3) << endl;




        // Lets display the output of the detector along with our training images.
        image_window win;
        for (unsigned long i = 0; i < images.size(); ++i)
        {
            // Run the detector on images[i] 
            const std::vector<rectangle> rects = detector(images[i]);
            cout << "Number of detections: "<< rects.size() << endl;

            // Put the image and detections into the window.
            win.clear_overlay();
            win.set_image(images[i]);
            for (unsigned long j = 0; j < rects.size(); ++j)
            {
                // Add each detection as a red box.
                win.add_overlay(image_display::overlay_rect(rects[j], rgb_pixel(255,0,0)));
            }

            cout << "Hit enter to see the next image.";
            cin.get();
        }

        


        // Finally, note that the detector can be serialized to disk just like other dlib objects.
        ofstream fout("object_detector.dat", ios::binary);
        serialize(detector, fout);
        fout.close();

        // Recall from disk.
        ifstream fin("object_detector.dat", ios::binary);
        deserialize(detector, fin);
    }
    catch (exception& e)
    {
        cout << "\nexception thrown!" << endl;
        cout << e.what() << endl;
    }
    catch (...)
    {
        cout << "Some error occurred" << endl;
    }
}

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