main.cpp

#include <dlib/xml_parser.h>
#include <dlib/matrix.h>
#include <fstream>
#include <vector>
#include <stack>
#include <set>
#include <dlib/string.h>

using namespace std;
using namespace dlib;


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

// Only these computational layers have parameters
const std::set<string> comp_tags_with_params = {"fc", "fc_no_bias", "con", "affine_con", "affine_fc", "affine", "prelu"};

struct layer
{
    string type; // comp, loss, or input
    int idx;

    matrix<long,4,1> output_tensor_shape; // (N,K,NR,NC)

    string detail_name; // The name of the tag inside the layer tag. e.g. fc, con, max_pool, input_rgb_image.
    std::map<string,double> attributes;
    matrix<double> params;
    long tag_id = -1;   // If this isn't -1 then it means this layer was tagged, e.g. wrapped with tag2<> giving tag_id==2
    long skip_id = -1;  // If this isn't -1 then it means this layer draws its inputs from
                        // the most recent layer with tag_id==skip_id rather than its immediate predecessor. 

    double attribute (const string& key) const
    {
        auto i = attributes.find(key);
        if (i != attributes.end())
            return i->second;
        else
            throw dlib::error("Layer doesn't have the requested attribute '" + key + "'.");
    }

    string caffe_layer_name() const 
    { 
        if (type == "input")
            return "data";
        else
            return detail_name+to_string(idx);
    }
};

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

std::vector<layer> parse_dlib_xml(
    const matrix<long,4,1>& input_tensor_shape, 
    const string& xml_filename
);

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

template <typename iterator>
const layer& find_layer (
    iterator i,
    long tag_id
)
/*!
    requires
        - i is a reverse iterator pointing to a layer in the list of layers produced by parse_dlib_xml().
        - i is not an input layer.
    ensures
        - if (tag_id == -1) then
            - returns the previous layer (i.e. closer to the input) to layer i.
        - else
            - returns the previous layer (i.e. closer to the input) to layer i with the
              given tag_id.
!*/
{
    if (tag_id == -1)
    {
        return *(i-1);
    }
    else
    {
        while(true)
        {
            i--;
            // if we hit the end of the network before we found what we were looking for
            if (i->tag_id == tag_id)
                return *i;
            if (i->type == "input")
                throw dlib::error("Network definition is bad, a layer wanted to skip back to a non-existing layer.");
        }
    }
}

template <typename iterator>
const layer& find_input_layer (iterator i) { return find_layer(i, i->skip_id); }

template <typename iterator>
string find_layer_caffe_name (
    iterator i,
    long tag_id
)
{
    return find_layer(i,tag_id).caffe_layer_name();
}

template <typename iterator>
string find_input_layer_caffe_name (iterator i) { return find_input_layer(i).caffe_layer_name(); }

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

template <typename EXP>
void print_as_np_array(std::ostream& out, const matrix_exp<EXP>& m)
{
    out << "np.array([";
    for (auto x : m)
        out << x << ",";
    out << "], dtype='float32')";
}

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

void convert_dlib_xml_to_caffe_python_code(
    const string& xml_filename,
    const long N,
    const long K,
    const long NR,
    const long NC
)
{
    const string out_filename = left_substr(xml_filename,".") + "_dlib_to_caffe_model.py";
    cout << "Writing model to " << out_filename << endl;
    ofstream fout(out_filename);
    fout.precision(9);
    const auto layers = parse_dlib_xml({N,K,NR,NC}, xml_filename);


    fout << "#\n";
    fout << "# !!! This file was automatically generated by dlib's tools/convert_dlib_nets_to_caffe utility.     !!!\n";
    fout << "# !!! It contains all the information from a dlib DNN network and lets you save it as a cafe model. !!!\n";
    fout << "#\n";
    fout << "import caffe " << endl;
    fout << "from caffe import layers as L, params as P" << endl;
    fout << "import numpy as np" << endl;

    // dlib nets don't commit to a batch size, so just use 1 as the default
    fout << "\n# Input tensor dimensions" << endl;
    fout << "input_batch_size = " << N << ";" << endl;
    if (layers.back().detail_name == "input_rgb_image")
    {
        fout << "input_num_channels = 3;" << endl;
        fout << "input_num_rows = "<<NR<<";" << endl;
        fout << "input_num_cols = "<<NC<<";" << endl;
        if (K != 3)
            throw dlib::error("The dlib model requires input tensors with NUM_CHANNELS==3, but the dtoc command line specified NUM_CHANNELS=="+to_string(K));
    }
    else if (layers.back().detail_name == "input_rgb_image_sized")
    {
        fout << "input_num_channels = 3;" << endl;
        fout << "input_num_rows = " << layers.back().attribute("nr") << ";" << endl;
        fout << "input_num_cols = " << layers.back().attribute("nc") << ";" << endl;
        if (NR != layers.back().attribute("nr"))
            throw dlib::error("The dlib model requires input tensors with NUM_ROWS=="+to_string((long)layers.back().attribute("nr"))+", but the dtoc command line specified NUM_ROWS=="+to_string(NR));
        if (NC != layers.back().attribute("nc"))
            throw dlib::error("The dlib model requires input tensors with NUM_COLUMNS=="+to_string((long)layers.back().attribute("nc"))+", but the dtoc command line specified NUM_COLUMNS=="+to_string(NC));
        if (K != 3)
            throw dlib::error("The dlib model requires input tensors with NUM_CHANNELS==3, but the dtoc command line specified NUM_CHANNELS=="+to_string(K));
    }
    else if (layers.back().detail_name == "input")
    {
        fout << "input_num_channels = 1;" << endl;
        fout << "input_num_rows = "<<NR<<";" << endl;
        fout << "input_num_cols = "<<NC<<";" << endl;
        if (K != 1)
            throw dlib::error("The dlib model requires input tensors with NUM_CHANNELS==1, but the dtoc command line specified NUM_CHANNELS=="+to_string(K));
    }
    else
    {
        throw dlib::error("No known transformation from dlib's " + layers.back().detail_name + " layer to caffe.");
    }
    fout << endl;
    fout << "# Call this function to write the dlib DNN model out to file as a pair of caffe\n";
    fout << "# definition and weight files.  You can then use the network by loading it with\n";
    fout << "# this statement: \n";
    fout << "#    net = caffe.Net(def_file, weights_file, caffe.TEST);\n";
    fout << "#\n";
    fout << "def save_as_caffe_model(def_file, weights_file):\n";
    fout << "    with open(def_file, 'w') as f: f.write(str(make_netspec()));\n";
    fout << "    net = caffe.Net(def_file, caffe.TEST);\n";
    fout << "    set_network_weights(net);\n";
    fout << "    net.save(weights_file);\n\n";
    fout << "###############################################################################\n";
    fout << "#         EVERYTHING BELOW HERE DEFINES THE DLIB MODEL PARAMETERS             #\n";
    fout << "###############################################################################\n\n\n";


    // -----------------------------------------------------------------------------------
    //  The next block of code outputs python code that defines the network architecture. 
    // -----------------------------------------------------------------------------------

    fout << "def make_netspec():" << endl;
    fout << "    # For reference, the only \"documentation\" about caffe layer parameters seems to be this page:\n";
    fout << "    # https://github.com/BVLC/caffe/blob/master/src/caffe/proto/caffe.proto\n" << endl;
    fout << "    n = caffe.NetSpec(); " << endl;
    fout << "    n.data,n.label = L.MemoryData(batch_size=input_batch_size, channels=input_num_channels, height=input_num_rows, width=input_num_cols, ntop=2)" << endl;
    // iterate the layers starting with the input layer
    for (auto i = layers.rbegin(); i != layers.rend(); ++i)
    {
        // skip input and loss layers
        if (i->type == "loss" || i->type == "input")
            continue;


        if (i->detail_name == "con")
        {
            fout << "    n." << i->caffe_layer_name() << " = L.Convolution(n." << find_input_layer_caffe_name(i);
            fout << ", num_output=" << i->attribute("num_filters");
            fout << ", kernel_w=" << i->attribute("nc");
            fout << ", kernel_h=" << i->attribute("nr");
            fout << ", stride_w=" << i->attribute("stride_x");
            fout << ", stride_h=" << i->attribute("stride_y");
            fout << ", pad_w=" << i->attribute("padding_x");
            fout << ", pad_h=" << i->attribute("padding_y");
            fout << ");\n";
        }
        else if (i->detail_name == "relu")
        {
            fout << "    n." << i->caffe_layer_name() << " = L.ReLU(n." << find_input_layer_caffe_name(i);
            fout << ");\n";
        }
        else if (i->detail_name == "sig")
        {
            fout << "    n." << i->caffe_layer_name() << " = L.Sigmoid(n." << find_input_layer_caffe_name(i);
            fout << ");\n";
        }
        else if (i->detail_name == "prelu")
        {
            fout << "    n." << i->caffe_layer_name() << " = L.PReLU(n." << find_input_layer_caffe_name(i);
            fout << ", channel_shared=True"; 
            fout << ");\n";
        }
        else if (i->detail_name == "max_pool")
        {
            fout << "    n." << i->caffe_layer_name() << " = L.Pooling(n." << find_input_layer_caffe_name(i);
            fout << ", pool=P.Pooling.MAX"; 
            if (i->attribute("nc")==0)
            {
                fout << ", global_pooling=True";
            }
            else
            {
                fout << ", kernel_w=" << i->attribute("nc");
                fout << ", kernel_h=" << i->attribute("nr");
            }

            fout << ", stride_w=" << i->attribute("stride_x");
            fout << ", stride_h=" << i->attribute("stride_y");
            fout << ", pad_w=" << i->attribute("padding_x");
            fout << ", pad_h=" << i->attribute("padding_y");
            fout << ");\n";
        }
        else if (i->detail_name == "avg_pool")
        {
            fout << "    n." << i->caffe_layer_name() << " = L.Pooling(n." << find_input_layer_caffe_name(i);
            fout << ", pool=P.Pooling.AVE"; 
            if (i->attribute("nc")==0)
            {
                fout << ", global_pooling=True";
            }
            else
            {
                fout << ", kernel_w=" << i->attribute("nc");
                fout << ", kernel_h=" << i->attribute("nr");
            }
            if (i->attribute("padding_x") != 0 || i->attribute("padding_y") != 0)
            {
                throw dlib::error("dlib and caffe implement pooling with non-zero padding differently, so you can't convert a "
                    "network with such pooling layers.");
            }

            fout << ", stride_w=" << i->attribute("stride_x");
            fout << ", stride_h=" << i->attribute("stride_y");
            fout << ", pad_w=" << i->attribute("padding_x");
            fout << ", pad_h=" << i->attribute("padding_y");
            fout << ");\n";
        }
        else if (i->detail_name == "fc")
        {
            fout << "    n." << i->caffe_layer_name() << " = L.InnerProduct(n." << find_input_layer_caffe_name(i);
            fout << ", num_output=" << i->attribute("num_outputs");
            fout << ", bias_term=True";
            fout << ");\n";
        }
        else if (i->detail_name == "fc_no_bias")
        {
            fout << "    n." << i->caffe_layer_name() << " = L.InnerProduct(n." << find_input_layer_caffe_name(i);
            fout << ", num_output=" << i->attribute("num_outputs");
            fout << ", bias_term=False";
            fout << ");\n";
        }
        else if (i->detail_name == "bn_con" || i->detail_name == "bn_fc")
        {
            throw dlib::error("Conversion from dlib's batch norm layers to caffe's isn't supported.  Instead, "
                "you should put your dlib network into 'test mode' by switching batch norm layers to affine layers. "
                "Then you can convert that 'test mode' network to caffe.");
        }
        else if (i->detail_name == "affine_con")
        {
            fout << "    n." << i->caffe_layer_name() << " = L.Scale(n." << find_input_layer_caffe_name(i);
            fout << ", bias_term=True";
            fout << ");\n";
        }
        else if (i->detail_name == "affine_fc")
        {
            fout << "    n." << i->caffe_layer_name() << " = L.Scale(n." << find_input_layer_caffe_name(i);
            fout << ", bias_term=True";
            fout << ");\n";
        }
        else if (i->detail_name == "add_prev")
        {
            auto in_shape1 = find_input_layer(i).output_tensor_shape;
            auto in_shape2 = find_layer(i,i->attribute("tag")).output_tensor_shape;
            if (in_shape1 != in_shape2)
            {
                // if only the number of channels differs then we will use a dummy layer to
                // pad with zeros.  But otherwise we will throw an error.
                if (in_shape1(0) == in_shape2(0) && 
                    in_shape1(2) == in_shape2(2) && 
                    in_shape1(3) == in_shape2(3))
                {
                    fout << "    n." << i->caffe_layer_name() << "_zeropad = L.DummyData(num=" << in_shape1(0);
                    fout << ", channels="<<std::abs(in_shape1(1)-in_shape2(1));
                    fout << ", height="<<in_shape1(2);
                    fout << ", width="<<in_shape1(3);
                    fout << ");\n";

                    string smaller_layer = find_input_layer_caffe_name(i);
                    string bigger_layer = find_layer_caffe_name(i, i->attribute("tag"));
                    if (in_shape1(1) > in_shape2(1))
                        swap(smaller_layer, bigger_layer);

                    fout << "    n." << i->caffe_layer_name() << "_concat = L.Concat(n." << smaller_layer;
                    fout << ", n." << i->caffe_layer_name() << "_zeropad";
                    fout << ");\n";

                    fout << "    n." << i->caffe_layer_name() << " = L.Eltwise(n." << i->caffe_layer_name() << "_concat";
                    fout << ", n." << bigger_layer;
                    fout << ", operation=P.Eltwise.SUM";
                    fout << ");\n";
                }
                else
                {
                    std::ostringstream sout;
                    sout << "The dlib network contained an add_prev layer (layer idx " << i->idx << ") that adds two previous ";
                    sout << "layers with different output tensor dimensions.  Caffe's equivalent layer, Eltwise, doesn't support ";
                    sout << "adding layers together with different dimensions.  In the special case where the only difference is "; 
                    sout << "in the number of channels, this converter program will add a dummy layer that outputs a tensor full of zeros ";
                    sout << "and concat it appropriately so this will work.  However, this network you are converting has tensor dimensions ";
                    sout << "different in values other than the number of channels.  In particular, here are the two tensor shapes (batch size, channels, rows, cols): ";
                    std::ostringstream sout2;
                    sout2 << wrap_string(sout.str()) << endl;
                    sout2 << trans(in_shape1);
                    sout2 << trans(in_shape2);
                    throw dlib::error(sout2.str());
                }
            }
            else
            {
                fout << "    n." << i->caffe_layer_name() << " = L.Eltwise(n." << find_input_layer_caffe_name(i);
                fout << ", n." << find_layer_caffe_name(i, i->attribute("tag"));
                fout << ", operation=P.Eltwise.SUM";
                fout << ");\n";
            }
        }
        else
        {
            throw dlib::error("No known transformation from dlib's " + i->detail_name + " layer to caffe.");
        }
    }
    fout << "    return n.to_proto();\n\n" << endl;


    // -----------------------------------------------------------------------------------
    //  The next block of code outputs python code that populates all the filter weights.
    // -----------------------------------------------------------------------------------

    fout << "def set_network_weights(net):\n";
    fout << "    # populate network parameters\n";
    // iterate the layers starting with the input layer
    for (auto i = layers.rbegin(); i != layers.rend(); ++i)
    {
        // skip input and loss layers
        if (i->type == "loss" || i->type == "input")
            continue;


        if (i->detail_name == "con")
        {
            const long num_filters = i->attribute("num_filters");
            matrix<double> weights = trans(rowm(i->params,range(0,i->params.size()-num_filters-1)));
            matrix<double> biases  = trans(rowm(i->params,range(i->params.size()-num_filters, i->params.size()-1)));

            // main filter weights
            fout << "    p = "; print_as_np_array(fout,weights); fout << ";\n";
            fout << "    p.shape = net.params['"<<i->caffe_layer_name()<<"'][0].data.shape;\n";
            fout << "    net.params['"<<i->caffe_layer_name()<<"'][0].data[:] = p;\n";

            // biases
            fout << "    p = "; print_as_np_array(fout,biases); fout << ";\n";
            fout << "    p.shape = net.params['"<<i->caffe_layer_name()<<"'][1].data.shape;\n";
            fout << "    net.params['"<<i->caffe_layer_name()<<"'][1].data[:] = p;\n";
        }
        else if (i->detail_name == "fc")
        {
            matrix<double> weights = trans(rowm(i->params, range(0,i->params.nr()-2))); 
            matrix<double> biases  = rowm(i->params, i->params.nr()-1); 

            // main filter weights
            fout << "    p = "; print_as_np_array(fout,weights); fout << ";\n";
            fout << "    p.shape = net.params['"<<i->caffe_layer_name()<<"'][0].data.shape;\n";
            fout << "    net.params['"<<i->caffe_layer_name()<<"'][0].data[:] = p;\n";

            // biases
            fout << "    p = "; print_as_np_array(fout,biases); fout << ";\n";
            fout << "    p.shape = net.params['"<<i->caffe_layer_name()<<"'][1].data.shape;\n";
            fout << "    net.params['"<<i->caffe_layer_name()<<"'][1].data[:] = p;\n";
        }
        else if (i->detail_name == "fc_no_bias")
        {
            matrix<double> weights = trans(i->params); 

            // main filter weights
            fout << "    p = "; print_as_np_array(fout,weights); fout << ";\n";
            fout << "    p.shape = net.params['"<<i->caffe_layer_name()<<"'][0].data.shape;\n";
            fout << "    net.params['"<<i->caffe_layer_name()<<"'][0].data[:] = p;\n";
        }
        else if (i->detail_name == "affine_con" || i->detail_name == "affine_fc")
        {
            const long dims = i->params.size()/2;
            matrix<double> gamma = trans(rowm(i->params,range(0,dims-1)));
            matrix<double> beta  = trans(rowm(i->params,range(dims, 2*dims-1)));

            // set gamma weights
            fout << "    p = "; print_as_np_array(fout,gamma); fout << ";\n";
            fout << "    p.shape = net.params['"<<i->caffe_layer_name()<<"'][0].data.shape;\n";
            fout << "    net.params['"<<i->caffe_layer_name()<<"'][0].data[:] = p;\n";

            // set beta weights 
            fout << "    p = "; print_as_np_array(fout,beta); fout << ";\n";
            fout << "    p.shape = net.params['"<<i->caffe_layer_name()<<"'][1].data.shape;\n";
            fout << "    net.params['"<<i->caffe_layer_name()<<"'][1].data[:] = p;\n";
        }
        else if (i->detail_name == "prelu")
        {
            const double param = i->params(0);

            // main filter weights
            fout << "    tmp = net.params['"<<i->caffe_layer_name()<<"'][0].data.view();\n";
            fout << "    tmp.shape = 1;\n";
            fout << "    tmp[0] = "<<param<<";\n";
        }
    }

}

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

int main(int argc, char** argv) try
{
    if (argc != 6)
    {
        cout << "To use this program, give it an xml file generated by dlib::net_to_xml() " << endl;
        cout << "and then 4 numbers that indicate the input tensor size.  It will convert " << endl;
        cout << "the xml file into a python file that outputs a caffe model containing the dlib model." << endl;
        cout << "For example, you might run this program like this: " << endl;
        cout << "   ./dtoc lenet.xml 1 1 28 28" << endl;
        cout << "would convert the lenet.xml model into a caffe model with an input tensor of shape(1,1,28,28)" << endl;
        cout << "where the shape values are (num samples in batch, num channels, num rows, num columns)." << endl;
        return 0;
    }

    const long N = sa = argv[2];
    const long K = sa = argv[3];
    const long NR = sa = argv[4];
    const long NC = sa = argv[5];

    convert_dlib_xml_to_caffe_python_code(argv[1], N, K, NR, NC);

    return 0;
}
catch(std::exception& e)
{
    cout << "\n\n*************** ERROR CONVERTING TO CAFFE ***************\n" << e.what() << endl;
    return 1;
}

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

class doc_handler : public document_handler
{
public:
    std::vector<layer> layers;
    bool seen_first_tag = false;

    layer next_layer;
    std::stack<string> current_tag;
    long tag_id = -1;


    virtual void start_document (
    ) 
    { 
        layers.clear(); 
        seen_first_tag = false;
        tag_id = -1;
    }

    virtual void end_document (
    ) { }

    virtual void start_element ( 
        const unsigned long line_number,
        const std::string& name,
        const dlib::attribute_list& atts
    )
    {
        if (!seen_first_tag)
        {
            if (name != "net")
                throw dlib::error("The top level XML tag must be a 'net' tag.");
            seen_first_tag = true;
        }

        if (name == "layer")
        {
            next_layer = layer();
            if (atts["type"] == "skip")
            {
                // Don't make a new layer, just apply the tag id to the previous layer
                if (layers.size() == 0)
                    throw dlib::error("A skip layer was found as the first layer, but the first layer should be an input layer.");
                layers.back().skip_id = sa = atts["id"];
                
                // We intentionally leave next_layer empty so the end_element() callback
                // don't add it as another layer when called.
            }
            else if (atts["type"] == "tag")
            {
                // Don't make a new layer, just remember the tag id so we can apply it on
                // the next layer.
                tag_id = sa = atts["id"];
                
                // We intentionally leave next_layer empty so the end_element() callback
                // don't add it as another layer when called.
            }
            else
            {
                next_layer.idx = sa = atts["idx"];
                next_layer.type = atts["type"];
                if (tag_id != -1)
                {
                    next_layer.tag_id = tag_id;
                    tag_id = -1;
                }
            }
        }
        else if (current_tag.size() != 0 && current_tag.top() == "layer")
        {
            next_layer.detail_name = name;
            // copy all the XML tag's attributes into the layer struct
            atts.reset();
            while (atts.move_next())
                next_layer.attributes[atts.element().key()] = sa = atts.element().value();
        }

        current_tag.push(name);
    }

    virtual void end_element ( 
        const unsigned long line_number,
        const std::string& name
    )
    {
        current_tag.pop();
        if (name == "layer" && next_layer.type.size() != 0)
            layers.push_back(next_layer);
    }

    virtual void characters ( 
        const std::string& data
    )
    {
        if (current_tag.size() == 0)
            return;

        if (comp_tags_with_params.count(current_tag.top()) != 0)
        {
            istringstream sin(data);
            sin >> next_layer.params;
        }

    }

    virtual void processing_instruction (
        const unsigned long line_number,
        const std::string& target,
        const std::string& data
    )
    {
    }
};

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

void compute_output_tensor_shapes(const matrix<long,4,1>& input_tensor_shape, std::vector<layer>& layers)
{
    DLIB_CASSERT(layers.back().type == "input");
    layers.back().output_tensor_shape = input_tensor_shape;
    for (auto i = ++layers.rbegin(); i != layers.rend(); ++i)
    {
        const auto input_shape = find_input_layer(i).output_tensor_shape;
        if (i->type == "comp")
        {
            if (i->detail_name == "fc" || i->detail_name == "fc_no_bias")
            {
                long num_outputs = i->attribute("num_outputs");
                i->output_tensor_shape = {input_shape(0), num_outputs, 1, 1};
            }
            else if (i->detail_name == "con")
            {
                long num_filters = i->attribute("num_filters");
                long filter_nc = i->attribute("nc");
                long filter_nr = i->attribute("nr");
                long stride_x = i->attribute("stride_x");
                long stride_y = i->attribute("stride_y");
                long padding_x = i->attribute("padding_x");
                long padding_y = i->attribute("padding_y");
                long nr = 1+(input_shape(2) + 2*padding_y - filter_nr)/stride_y;
                long nc = 1+(input_shape(3) + 2*padding_x - filter_nc)/stride_x;
                i->output_tensor_shape = {input_shape(0), num_filters, nr, nc};
            }
            else if (i->detail_name == "max_pool" || i->detail_name == "avg_pool")
            {
                long filter_nc = i->attribute("nc");
                long filter_nr = i->attribute("nr");
                long stride_x = i->attribute("stride_x");
                long stride_y = i->attribute("stride_y");
                long padding_x = i->attribute("padding_x");
                long padding_y = i->attribute("padding_y");
                long nr = 1+(input_shape(2) + 2*padding_y - filter_nr)/stride_y;
                long nc = 1+(input_shape(3) + 2*padding_x - filter_nc)/stride_x;
                i->output_tensor_shape = {input_shape(0), input_shape(1), nr, nc};
            }
            else if (i->detail_name == "add_prev")
            {
                auto aux_shape = find_layer(i, i->attribute("tag")).output_tensor_shape;
                for (long j = 0; j < input_shape.size(); ++j)
                    i->output_tensor_shape(j) = std::max(input_shape(j), aux_shape(j));
            }
            else
            {
                i->output_tensor_shape = input_shape;
            }
        }
        else
        {
            i->output_tensor_shape = input_shape;
        }

    }
}

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

std::vector<layer> parse_dlib_xml(
    const matrix<long,4,1>& input_tensor_shape, 
    const string& xml_filename
)
{
    doc_handler dh;
    parse_xml(xml_filename, dh);
    if (dh.layers.size() == 0)
        throw dlib::error("No layers found in XML file!");

    if (dh.layers.back().type != "input")
        throw dlib::error("The network in the XML file is missing an input layer!");

    compute_output_tensor_shapes(input_tensor_shape, dh.layers);

    return dh.layers;
}

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