# dlib C++ Library - dnn_semantic_segmentation_ex.cpp

    // The contents of this file are in the public domain. See LICENSE_FOR_EXAMPLE_PROGRAMS.txt
    /*
        This example shows how to do semantic segmentation on an image using net pretrained
        on the PASCAL VOC2012 dataset.  For an introduction to what segmentation is, see the
        accompanying header file dnn_semantic_segmentation_ex.h.

        Instructions how to run the example:
        1. Download the PASCAL VOC2012 data, and untar it somewhere.
           http://host.robots.ox.ac.uk/pascal/VOC/voc2012/VOCtrainval_11-May-2012.tar
        2. Build the dnn_semantic_segmentation_train_ex example program.
        3. Run:
           ./dnn_semantic_segmentation_train_ex /path/to/VOC2012
        4. Wait while the network is being trained.
        5. Build the dnn_semantic_segmentation_ex example program.
        6. Run:
           ./dnn_semantic_segmentation_ex /path/to/VOC2012-or-other-images

        An alternative to steps 2-4 above is to download a pre-trained network
        from here: http://dlib.net/files/semantic_segmentation_voc2012net_v2.dnn

        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.
    */

    #include "dnn_semantic_segmentation_ex.h"

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

    using namespace std;
    using namespace dlib;

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

    // The PASCAL VOC2012 dataset contains 20 ground-truth classes + background.  Each class
    // is represented using an RGB color value.  We associate each class also to an index in the
    // range [0, 20], used internally by the network.  To generate nice RGB representations of
    // inference results, we need to be able to convert the index values to the corresponding
    // RGB values.

    // Given an index in the range [0, 20], find the corresponding PASCAL VOC2012 class
    // (e.g., 'dog').
    const Voc2012class& find_voc2012_class(const uint16_t& index_label)
    {
        return find_voc2012_class(
            [&index_label](const Voc2012class& voc2012class)
            {
                return index_label == voc2012class.index;
            }
        );
    }

    // Convert an index in the range [0, 20] to a corresponding RGB class label.
    inline rgb_pixel index_label_to_rgb_label(uint16_t index_label)
    {
        return find_voc2012_class(index_label).rgb_label;
    }

    // Convert an image containing indexes in the range [0, 20] to a corresponding
    // image containing RGB class labels.
    void index_label_image_to_rgb_label_image(
        const matrix<uint16_t>& index_label_image,
        matrix<rgb_pixel>& rgb_label_image
    )
    {
        const long nr = index_label_image.nr();
        const long nc = index_label_image.nc();

        rgb_label_image.set_size(nr, nc);

        for (long r = 0; r < nr; ++r)
        {
            for (long c = 0; c < nc; ++c)
            {
                rgb_label_image(r, c) = index_label_to_rgb_label(index_label_image(r, c));
            }
        }
    }

    // Find the most prominent class label from amongst the per-pixel predictions.
    std::string get_most_prominent_non_background_classlabel(const matrix<uint16_t>& index_label_image)
    {
        const long nr = index_label_image.nr();
        const long nc = index_label_image.nc();

        std::vector<unsigned int> counters(class_count);

        for (long r = 0; r < nr; ++r)
        {
            for (long c = 0; c < nc; ++c)
            {
                const uint16_t label = index_label_image(r, c);
                ++counters[label];
            }
        }

        const auto max_element = std::max_element(counters.begin() + 1, counters.end());
        const uint16_t most_prominent_index_label = max_element - counters.begin();

        return find_voc2012_class(most_prominent_index_label).classlabel;
    }

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

    int main(int argc, char** argv) try
    {
        if (argc != 2)
        {
            cout << "You call this program like this: " << endl;
            cout << "./dnn_semantic_segmentation_train_ex /path/to/images" << endl;
            cout << endl;
            cout << "You will also need a trained '" << semantic_segmentation_net_filename << "' file." << endl;
            cout << "You can either train it yourself (see example program" << endl;
            cout << "dnn_semantic_segmentation_train_ex), or download a" << endl;
            cout << "copy from here: http://dlib.net/files/" << semantic_segmentation_net_filename << endl;
            return 1;
        }

        // Read the file containing the trained network from the working directory.
        anet_type net;
        deserialize(semantic_segmentation_net_filename) >> net;

        // Show inference results in a window.
        image_window win;

        matrix<rgb_pixel> input_image;
        matrix<uint16_t> index_label_image;
        matrix<rgb_pixel> rgb_label_image;

        // Find supported image files.
        const std::vector<file> files = dlib::get_files_in_directory_tree(argv[1],
            dlib::match_endings(".jpeg .jpg .png"));

        cout << "Found " << files.size() << " images, processing..." << endl;

        for (const file& file : files)
        {
            // Load the input image.
            load_image(input_image, file.full_name());

            // Create predictions for each pixel. At this point, the type of each prediction
            // is an index (a value between 0 and 20). Note that the net may return an image
            // that is not exactly the same size as the input.
            const matrix<uint16_t> temp = net(input_image);

            // Crop the returned image to be exactly the same size as the input.
            const chip_details chip_details(
                centered_rect(temp.nc() / 2, temp.nr() / 2, input_image.nc(), input_image.nr()),
                chip_dims(input_image.nr(), input_image.nc())
            );
            extract_image_chip(temp, chip_details, index_label_image, interpolate_nearest_neighbor());

            // Convert the indexes to RGB values.
            index_label_image_to_rgb_label_image(index_label_image, rgb_label_image);

            // Show the input image on the left, and the predicted RGB labels on the right.
            win.set_image(join_rows(input_image, rgb_label_image));

            // Find the most prominent class label from amongst the per-pixel predictions.
            const std::string classlabel = get_most_prominent_non_background_classlabel(index_label_image);

            cout << file.name() << " : " << classlabel << " - hit enter to process the next image";
            cin.get();
        }
    }
    catch(std::exception& e)
    {
        cout << e.what() << endl;
    }