# dlib C++ Library - dnn_mmod_ex.cpp

    // The contents of this file are in the public domain. See LICENSE_FOR_EXAMPLE_PROGRAMS.txt
    /*
        This example shows how to train a CNN based object detector using dlib's
        loss_mmod loss layer.  This loss layer implements the Max-Margin Object
        Detection loss as described in the paper:
            Max-Margin Object Detection by Davis E. King (http://arxiv.org/abs/1502.00046).
        This is the same loss used by the popular SVM+HOG object detector in dlib
        (see fhog_object_detector_ex.cpp) except here we replace the HOG features
        with a CNN and train the entire detector end-to-end.  This allows us to make
        much more powerful detectors.

        It would be a good idea to become familiar with dlib's DNN tooling before
        reading this example.  So you should read dnn_introduction_ex.cpp and
        dnn_introduction2_ex.cpp before reading this example program.

        Just like in the fhog_object_detector_ex.cpp example, we are going to train
        a simple face detector based on the very small training dataset in the
        examples/faces folder.  As we will see, even with this small dataset the
        MMOD method is able to make a working face detector.  However, for real
        applications you should train with more data for an even better result.
    */

    #include <iostream>
    #include <dlib/dnn.h>
    #include <dlib/data_io.h>
    #include <dlib/gui_widgets.h>

    using namespace std;
    using namespace dlib;

    // The first thing we do is define our CNN.  The CNN is going to be evaluated
    // convolutionally over an entire image pyramid.  Think of it like a normal
    // sliding window classifier.  This means you need to define a CNN that can look
    // at some part of an image and decide if it is an object of interest.  In this
    // example I've defined a CNN with a receptive field of approximately 50x50
    // pixels.  This is reasonable for face detection since you can clearly tell if
    // a 50x50 image contains a face.  Other applications may benefit from CNNs with
    // different architectures.
    //
    // In this example our CNN begins with 3 downsampling layers.  These layers will
    // reduce the size of the image by 8x and output a feature map with
    // 32 dimensions.  Then we will pass that through 4 more convolutional layers to
    // get the final output of the network.  The last layer has only 1 channel and
    // the values in that last channel are large when the network thinks it has
    // found an object at a particular location.

    // Let's begin the network definition by creating some network blocks.

    // A 5x5 conv layer that does 2x downsampling
    template <long num_filters, typename SUBNET> using con5d = con<num_filters,5,5,2,2,SUBNET>;
    // A 3x3 conv layer that doesn't do any downsampling
    template <long num_filters, typename SUBNET> using con3  = con<num_filters,3,3,1,1,SUBNET>;

    // Now we can define the 8x downsampling block in terms of conv5d blocks.  We
    // also use relu and batch normalization in the standard way.
    template <typename SUBNET> using downsampler  = relu<bn_con<con5d<32, relu<bn_con<con5d<32, relu<bn_con<con5d<32,SUBNET>>>>>>>>>;

    // The rest of the network will be 3x3 conv layers with batch normalization and
    // relu.  So we define the 3x3 block we will use here.
    template <typename SUBNET> using rcon3  = relu<bn_con<con3<32,SUBNET>>>;

    // Finally, we define the entire network.   The special input_rgb_image_pyramid
    // layer causes the network to operate over a spatial pyramid, making the detector
    // scale invariant.
    using net_type  = loss_mmod<con<1,6,6,1,1,rcon3<rcon3<rcon3<downsampler<input_rgb_image_pyramid<pyramid_down<6>>>>>>>>;

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

    int main(int argc, char** argv) try
    {
        // In this example we are going to train a face detector based on the
        // small faces dataset in the examples/faces directory.  So the first
        // thing we do is load that dataset.  This means you need to supply the
        // path to this faces folder as a command line argument so we will know
        // where it is.
        if (argc != 2)
        {
            cout << "Give the path to the examples/faces directory as the argument to this" << endl;
            cout << "program.  For example, if you are in the examples folder then execute " << endl;
            cout << "this program by running: " << endl;
            cout << "   ./dnn_mmod_ex faces" << endl;
            cout << endl;
            return 0;
        }
        const std::string faces_directory = argv[1];
        // The faces directory contains a training dataset and a separate
        // testing dataset.  The training data consists of 4 images, each
        // annotated with rectangles that bound each human face.  The idea is
        // to use this training data to learn to identify human faces in new
        // images.
        //
        // Once you have trained an object detector it is always important to
        // test it on data it wasn't trained on.  Therefore, we will also load
        // a separate testing set of 5 images.  Once we have a face detector
        // created from the training data we will see how well it works by
        // running it on the testing images.
        //
        // So here we create the variables that will hold our dataset.
        // images_train will hold the 4 training images and face_boxes_train
        // holds the locations of the faces in the training images.  So for
        // example, the image images_train[0] has the faces given by the
        // rectangles in face_boxes_train[0].
        std::vector<matrix<rgb_pixel>> images_train, images_test;
        std::vector<std::vector<mmod_rect>> face_boxes_train, face_boxes_test;

        // Now we load the data.  These XML files list the images in each dataset
        // and also contain the positions of the face boxes.  Obviously you can use
        // any kind of input format you like so long as you store the data into
        // images_train and face_boxes_train.  But for convenience dlib comes with
        // tools for creating and loading XML image datasets.  Here you see how to
        // load the data.  To create the XML files you can use the imglab tool which
        // can be found in the tools/imglab folder.  It is a simple graphical tool
        // for labeling objects in images with boxes.  To see how to use it read the
        // tools/imglab/README.txt file.
        load_image_dataset(images_train, face_boxes_train, faces_directory+"/training.xml");
        load_image_dataset(images_test, face_boxes_test, faces_directory+"/testing.xml");

        cout << "num training images: " << images_train.size() << endl;
        cout << "num testing images:  " << images_test.size() << endl;

        // The MMOD algorithm has some options you can set to control its behavior.  However,
        // you can also call the constructor with your training annotations and a "target
        // object size" and it will automatically configure itself in a reasonable way for your
        // problem.  Here we are saying that faces are still recognizably faces when they are
        // 40x40 pixels in size.  You should generally pick the smallest size where this is
        // true.  Based on this information the mmod_options constructor will automatically
        // pick a good sliding window width and height.  It will also automatically set the
        // non-max-suppression parameters to something reasonable.  For further details see the
        // mmod_options documentation.
        mmod_options options(face_boxes_train, 40,40);
        // The detector will automatically decide to use multiple sliding windows if needed.
        // For the face data, only one is needed however.
        cout << "num detector windows: "<< options.detector_windows.size() << endl;
        for (auto& w : options.detector_windows)
            cout << "detector window width by height: " << w.width << " x " << w.height << endl;
        cout << "overlap NMS IOU thresh:             " << options.overlaps_nms.get_iou_thresh() << endl;
        cout << "overlap NMS percent covered thresh: " << options.overlaps_nms.get_percent_covered_thresh() << endl;

        // Now we are ready to create our network and trainer.
        net_type net(options);
        // The MMOD loss requires that the number of filters in the final network layer equal
        // options.detector_windows.size().  So we set that here as well.
        net.subnet().layer_details().set_num_filters(options.detector_windows.size());
        dnn_trainer<net_type> trainer(net);
        trainer.set_learning_rate(0.1);
        trainer.be_verbose();
        trainer.set_synchronization_file("mmod_sync", std::chrono::minutes(5));
        trainer.set_iterations_without_progress_threshold(300);

        // Now let's train the network.  We are going to use mini-batches of 150
        // images.   The images are random crops from our training set (see
        // random_cropper_ex.cpp for a discussion of the random_cropper).
        std::vector<matrix<rgb_pixel>> mini_batch_samples;
        std::vector<std::vector<mmod_rect>> mini_batch_labels;
        random_cropper cropper;
        cropper.set_chip_dims(200, 200);
        // Usually you want to give the cropper whatever min sizes you passed to the
        // mmod_options constructor, which is what we do here.
        cropper.set_min_object_size(40,40);
        dlib::rand rnd;
        // Run the trainer until the learning rate gets small.  This will probably take several
        // hours.
        while(trainer.get_learning_rate() >= 1e-4)
        {
            cropper(150, images_train, face_boxes_train, mini_batch_samples, mini_batch_labels);
            // We can also randomly jitter the colors and that often helps a detector
            // generalize better to new images.
            for (auto&& img : mini_batch_samples)
                disturb_colors(img, rnd);

            trainer.train_one_step(mini_batch_samples, mini_batch_labels);
        }
        // wait for training threads to stop
        trainer.get_net();
        cout << "done training" << endl;

        // Save the network to disk
        net.clean();
        serialize("mmod_network.dat") << net;

        // Now that we have a face detector we can test it.  The first statement tests it
        // on the training data.  It will print the precision, recall, and then average precision.
        // This statement should indicate that the network works perfectly on the
        // training data.
        cout << "training results: " << test_object_detection_function(net, images_train, face_boxes_train) << endl;
        // However, to get an idea if it really worked without overfitting we need to run
        // it on images it wasn't trained on.  The next line does this.   Happily,
        // this statement indicates that the detector finds most of the faces in the
        // testing data.
        cout << "testing results:  " << test_object_detection_function(net, images_test, face_boxes_test) << endl;

        // If you are running many experiments, it's also useful to log the settings used
        // during the training experiment.  This statement will print the settings we used to
        // the screen.
        cout << trainer << cropper << endl;

        // Now lets run the detector on the testing images and look at the outputs.
        image_window win;
        for (auto&& img : images_test)
        {
            pyramid_up(img);
            auto dets = net(img);
            win.clear_overlay();
            win.set_image(img);
            for (auto&& d : dets)
                win.add_overlay(d);
            cin.get();
        }
        return 0;

        // Now that you finished this example, you should read dnn_mmod_train_find_cars_ex.cpp,
        // which is a more advanced example.  It discusses many issues surrounding properly
        // setting the MMOD parameters and creating a good training dataset.

    }
    catch(std::exception& e)
    {
        cout << e.what() << endl;
    }