opencv/modules/contrib/src/facerec.cpp

/*
 * Copyright (c) 2011. Philipp Wagner <bytefish[at]gmx[dot]de>.
 * Released to public domain under terms of the BSD Simplified license.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *   * Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *   * Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *   * Neither the name of the organization nor the names of its contributors
 *     may be used to endorse or promote products derived from this software
 *     without specific prior written permission.
 *
 *   See <http://www.opensource.org/licenses/bsd-license>
 */
#include "precomp.hpp"
#include <set>

namespace cv
{

using std::set;
    
// Reads a sequence from a FileNode::SEQ with type _Tp into a result vector.
template<typename _Tp>
inline void readFileNodeList(const FileNode& fn, vector<_Tp>& result) {
    if (fn.type() == FileNode::SEQ) {
        for (FileNodeIterator it = fn.begin(); it != fn.end();) {
            _Tp item;
            it >> item;
            result.push_back(item);
        }
    }
}

// Writes the a list of given items to a cv::FileStorage.
template<typename _Tp>
inline void writeFileNodeList(FileStorage& fs, const string& name,
                              const vector<_Tp>& items) {
    // typedefs
    typedef typename vector<_Tp>::const_iterator constVecIterator;
    // write the elements in item to fs
    fs << name << "[";
    for (constVecIterator it = items.begin(); it != items.end(); ++it) {
        fs << *it;
    }
    fs << "]";
}
    
static Mat asRowMatrix(InputArrayOfArrays src, int rtype, double alpha=1, double beta=0)
{
    // number of samples
    int n = (int) src.total();
    // return empty matrix if no data given
    if(n == 0)
        return Mat();
    // dimensionality of samples
    int d = src.getMat(0).total();
    // create data matrix
    Mat data(n, d, rtype);
    // copy data
    for(int i = 0; i < n; i++) {
        Mat xi = data.row(i);
        src.getMat(i).reshape(1, 1).convertTo(xi, rtype, alpha, beta);
    }
    return data;
}
    
// Removes duplicate elements in a given vector.
template<typename _Tp>
inline vector<_Tp> remove_dups(const vector<_Tp>& src) {
    typedef typename set<_Tp>::const_iterator constSetIterator;
    typedef typename vector<_Tp>::const_iterator constVecIterator;
    set<_Tp> set_elems;
    for (constVecIterator it = src.begin(); it != src.end(); ++it)
        set_elems.insert(*it);
    vector<_Tp> elems;
    for (constSetIterator it = set_elems.begin(); it != set_elems.end(); ++it)
        elems.push_back(*it);
    return elems;
}

    
// Turk, M., and Pentland, A. "Eigenfaces for recognition.". Journal of
// Cognitive Neuroscience 3 (1991), 71–86.
class Eigenfaces : public FaceRecognizer
{
private:
    int _num_components;
    vector<Mat> _projections;
    vector<int> _labels;
    Mat _eigenvectors;
    Mat _eigenvalues;
    Mat _mean;

public:
    using FaceRecognizer::save;
    using FaceRecognizer::load;

    // Initializes an empty Eigenfaces model.
    Eigenfaces(int num_components = 0) :
        _num_components(num_components) { }

    // Initializes and computes an Eigenfaces model with images in src and
    // corresponding labels in labels. num_components will be kept for
    // classification.
    Eigenfaces(InputArray src, InputArray labels,
            int num_components = 0) :
        _num_components(num_components) {
        train(src, labels);
    }

    // Computes an Eigenfaces model with images in src and corresponding labels
    // in labels.
    void train(InputArray src, InputArray labels);

    // Predicts the label of a query image in src.
    int predict(const InputArray src) const;

    // See FaceRecognizer::load.
    void load(const FileStorage& fs);

    // See FaceRecognizer::save.
    void save(FileStorage& fs) const;

    // Returns the eigenvectors of this PCA.
    Mat eigenvectors() const { return _eigenvectors; }

    // Returns the eigenvalues of this PCA.
    Mat eigenvalues() const { return _eigenvalues; }

    // Returns the sample mean of this PCA.
    Mat mean() const { return _mean; }

    // Returns the number of components used in this PCA.
    int num_components() const { return _num_components; }
};

// Belhumeur, P. N., Hespanha, J., and Kriegman, D. "Eigenfaces vs. Fisher-
// faces: Recognition using class specific linear projection.". IEEE
// Transactions on Pattern Analysis and Machine Intelligence 19, 7 (1997),
// 711–720.
class Fisherfaces: public FaceRecognizer
{
private:
    int _num_components;
    Mat _eigenvectors;
    Mat _eigenvalues;
    Mat _mean;
    vector<Mat> _projections;
    vector<int> _labels;

public:
    using FaceRecognizer::save;
    using FaceRecognizer::load;

    // Initializes an empty Fisherfaces model.
    Fisherfaces(int num_components = 0) :
        _num_components(num_components) {}

    // Initializes and computes a Fisherfaces model with images in src and
    // corresponding labels in labels. num_components will be kept for
    // classification.
    Fisherfaces(InputArray src,
            InputArray labels,
            int num_components = 0) :
        _num_components(num_components) {
        train(src, labels);
    }

    ~Fisherfaces() { }

    // Computes a Fisherfaces model with images in src and corresponding labels
    // in labels.
    void train(InputArray src, InputArray labels);

    // Predicts the label of a query image in src.
    int predict(InputArray src) const;

    // See FaceRecognizer::load.
    virtual void load(const FileStorage& fs);

    // See FaceRecognizer::save.
    virtual void save(FileStorage& fs) const;

    // Returns the eigenvectors of this Fisherfaces model.
    Mat eigenvectors() const { return _eigenvectors; }

    // Returns the eigenvalues of this Fisherfaces model.
    Mat eigenvalues() const { return _eigenvalues; }

    // Returns the sample mean of this Fisherfaces model.
    Mat mean() const { return _eigenvalues; }

    // Returns the number of components used in this Fisherfaces model.
    int num_components() const { return _num_components; }
};

// Face Recognition based on Local Binary Patterns.
//
// TODO Allow to change the distance metric.
// TODO Allow to change LBP computation (Extended LBP used right now).
// TODO Optimize, Optimize, Optimize!
//
//  Ahonen T, Hadid A. and Pietikäinen M. "Face description with local binary
//  patterns: Application to face recognition." IEEE Transactions on Pattern
//  Analysis and Machine Intelligence, 28(12):2037-2041.
//
class LBPH : public FaceRecognizer
{
private:
    int _grid_x;
    int _grid_y;
    int _radius;
    int _neighbors;

    vector<Mat> _histograms;
    vector<int> _labels;

public:
    using FaceRecognizer::save;
    using FaceRecognizer::load;

    // Initializes this LBPH Model. The current implementation is rather fixed
    // as it uses the Extended Local Binary Patterns per default.
    //
    // radius, neighbors are used in the local binary patterns creation.
    // grid_x, grid_y control the grid size of the spatial histograms.
    LBPH(int radius=1, int neighbors=8, int grid_x=8, int grid_y=8) :
        _grid_x(grid_x),
        _grid_y(grid_y),
        _radius(radius),
        _neighbors(neighbors) {}

    // Initializes and computes this LBPH Model. The current implementation is
    // rather fixed as it uses the Extended Local Binary Patterns per default.
    //
    // (radius=1), (neighbors=8) are used in the local binary patterns creation.
    // (grid_x=8), (grid_y=8) controls the grid size of the spatial histograms.
    LBPH(InputArray src,
            InputArray labels,
            int radius=1, int neighbors=8,
            int grid_x=8, int grid_y=8) :
                _grid_x(grid_x),
                _grid_y(grid_y),
                _radius(radius),
                _neighbors(neighbors) {
        train(src, labels);
    }

    ~LBPH() { }

    // Computes a LBPH model with images in src and
    // corresponding labels in labels.
    void train(InputArray src, InputArray labels);

    // Predicts the label of a query image in src.
    int predict(InputArray src) const;

    // See FaceRecognizer::load.
    void load(const FileStorage& fs);

    // See FaceRecognizer::save.
    void save(FileStorage& fs) const;

    // Getter functions.
    int neighbors() const { return _neighbors; }
    int radius() const { return _radius; }
    int grid_x() const { return _grid_x; }
    int grid_y() const { return _grid_y; }

};


//------------------------------------------------------------------------------
// FaceRecognizer
//------------------------------------------------------------------------------
void FaceRecognizer::save(const string& filename) const {
    FileStorage fs(filename, FileStorage::WRITE);
    if (!fs.isOpened())
        CV_Error(CV_StsError, "File can't be opened for writing!");
    this->save(fs);
    fs.release();
}

void FaceRecognizer::load(const string& filename) {
    FileStorage fs(filename, FileStorage::READ);
    if (!fs.isOpened())
        CV_Error(CV_StsError, "File can't be opened for writing!");
    this->load(fs);
    fs.release();
}


//------------------------------------------------------------------------------
// Eigenfaces
//------------------------------------------------------------------------------
void Eigenfaces::train(InputArray src, InputArray _lbls) {
    // assert type
    if(_lbls.getMat().type() != CV_32SC1)
        CV_Error(CV_StsUnsupportedFormat, "Labels must be given as integer (CV_32SC1).");
    // get labels
    vector<int> labels = _lbls.getMat();
    // observations in row
    Mat data = asRowMatrix(src, CV_64FC1);
    // number of samples
    int n = data.rows;
    // dimensionality of data
    //int d = data.cols;
    // assert there are as much samples as labels
    if(n != labels.size())
        CV_Error(CV_StsBadArg, "The number of samples must equal the number of labels!");
    // clip number of components to be valid
    if((_num_components <= 0) || (_num_components > n))
        _num_components = n;
    // perform the PCA
    PCA pca(data, Mat(), CV_PCA_DATA_AS_ROW, _num_components);
    // copy the PCA results
    _mean = pca.mean.reshape(1,1); // store the mean vector
    _eigenvalues = pca.eigenvalues.clone(); // eigenvalues by row
    transpose(pca.eigenvectors, _eigenvectors); // eigenvectors by column
    _labels = labels; // store labels for prediction
    // save projections
    for(int sampleIdx = 0; sampleIdx < data.rows; sampleIdx++) {
        Mat p = subspaceProject(_eigenvectors, _mean, data.row(sampleIdx));
        this->_projections.push_back(p);
    }
}

int Eigenfaces::predict(InputArray _src) const {
    // get data
    Mat src = _src.getMat();
    // project into PCA subspace
    Mat q = subspaceProject(_eigenvectors, _mean, src.reshape(1,1));
    double minDist = DBL_MAX;
    int minClass = -1;
    for(int sampleIdx = 0; sampleIdx < _projections.size(); sampleIdx++) {
        double dist = norm(_projections[sampleIdx], q, NORM_L2);
        if(dist < minDist) {
            minDist = dist;
            minClass = _labels[sampleIdx];
        }
    }
    return minClass;
}

void Eigenfaces::load(const FileStorage& fs) {
    //read matrices
    fs["num_components"] >> _num_components;
    fs["mean"] >> _mean;
    fs["eigenvalues"] >> _eigenvalues;
    fs["eigenvectors"] >> _eigenvectors;
    // read sequences
    readFileNodeList(fs["projections"], _projections);
    readFileNodeList(fs["labels"], _labels);
}

void Eigenfaces::save(FileStorage& fs) const {
    // write matrices
    fs << "num_components" << _num_components;
    fs << "mean" << _mean;
    fs << "eigenvalues" << _eigenvalues;
    fs << "eigenvectors" << _eigenvectors;
    // write sequences
    writeFileNodeList(fs, "projections", _projections);
    writeFileNodeList(fs, "labels", _labels);
}

//------------------------------------------------------------------------------
// Fisherfaces
//------------------------------------------------------------------------------
void Fisherfaces::train(InputArray src, InputArray _lbls) {
    if(_lbls.getMat().type() != CV_32SC1)
            CV_Error(CV_StsUnsupportedFormat, "Labels must be given as integer (CV_32SC1).");
    // get data
    vector<int> labels = _lbls.getMat();
    Mat data = asRowMatrix(src, CV_64FC1);
    // dimensionality
    int N = data.rows; // number of samples
    //int D = data.cols; // dimension of samples
    // assert correct data alignment
    if(labels.size() != N)
        CV_Error(CV_StsUnsupportedFormat, "Labels must be given as integer (CV_32SC1).");
    // compute the Fisherfaces
    int C = remove_dups(labels).size(); // number of unique classes
    // clip number of components to be a valid number
    if((_num_components <= 0) || (_num_components > (C-1)))
        _num_components = (C-1);
    // perform a PCA and keep (N-C) components
    PCA pca(data, Mat(), CV_PCA_DATA_AS_ROW, (N-C));
    // project the data and perform a LDA on it
    LDA lda(pca.project(data),labels, _num_components);
    // store the total mean vector
    _mean = pca.mean.reshape(1,1);
    // store labels
    _labels = labels;
    // store the eigenvalues of the discriminants
    lda.eigenvalues().convertTo(_eigenvalues, CV_64FC1);
    // Now calculate the projection matrix as pca.eigenvectors * lda.eigenvectors.
    // Note: OpenCV stores the eigenvectors by row, so we need to transpose it!
    gemm(pca.eigenvectors, lda.eigenvectors(), 1.0, Mat(), 0.0, _eigenvectors, CV_GEMM_A_T);
    // store the projections of the original data
    for(int sampleIdx = 0; sampleIdx < data.rows; sampleIdx++) {
        Mat p = subspaceProject(_eigenvectors, _mean, data.row(sampleIdx));
        _projections.push_back(p);
    }
}

int Fisherfaces::predict(InputArray _src) const {
    Mat src = _src.getMat();
    // project into LDA subspace
    Mat q = subspaceProject(_eigenvectors, _mean, src.reshape(1,1));
    // find 1-nearest neighbor
    double minDist = DBL_MAX;
    int minClass = -1;
    for(int sampleIdx = 0; sampleIdx < _projections.size(); sampleIdx++) {
        double dist = norm(_projections[sampleIdx], q, NORM_L2);
        if(dist < minDist) {
            minDist = dist;
            minClass = _labels[sampleIdx];
        }
    }
    return minClass;
}


// See FaceRecognizer::load.
void Fisherfaces::load(const FileStorage& fs) {
    //read matrices
    fs["num_components"] >> _num_components;
    fs["mean"] >> _mean;
    fs["eigenvalues"] >> _eigenvalues;
    fs["eigenvectors"] >> _eigenvectors;
    // read sequences
    readFileNodeList(fs["projections"], _projections);
    readFileNodeList(fs["labels"], _labels);
}

// See FaceRecognizer::save.
void Fisherfaces::save(FileStorage& fs) const {
    // write matrices
    fs << "num_components" << _num_components;
    fs << "mean" << _mean;
    fs << "eigenvalues" << _eigenvalues;
    fs << "eigenvectors" << _eigenvectors;
    // write sequences
    writeFileNodeList(fs, "projections", _projections);
    writeFileNodeList(fs, "labels", _labels);
}
//------------------------------------------------------------------------------
// LBPH
//------------------------------------------------------------------------------

template <typename _Tp> static
void olbp_(InputArray _src, OutputArray _dst) {
    // get matrices
    Mat src = _src.getMat();
    // allocate memory for result
    _dst.create(src.rows-2, src.cols-2, CV_8UC1);
    Mat dst = _dst.getMat();
    // zero the result matrix
    dst.setTo(0);
    // calculate patterns
    for(int i=1;i<src.rows-1;i++) {
        for(int j=1;j<src.cols-1;j++) {
            _Tp center = src.at<_Tp>(i,j);
            unsigned char code = 0;
            code |= (src.at<_Tp>(i-1,j-1) >= center) << 7;
            code |= (src.at<_Tp>(i-1,j) >= center) << 6;
            code |= (src.at<_Tp>(i-1,j+1) >= center) << 5;
            code |= (src.at<_Tp>(i,j+1) >= center) << 4;
            code |= (src.at<_Tp>(i+1,j+1) >= center) << 3;
            code |= (src.at<_Tp>(i+1,j) >= center) << 2;
            code |= (src.at<_Tp>(i+1,j-1) >= center) << 1;
            code |= (src.at<_Tp>(i,j-1) >= center) << 0;
            dst.at<unsigned char>(i-1,j-1) = code;
        }
    }
}


//------------------------------------------------------------------------------
// cv::elbp
//------------------------------------------------------------------------------
template <typename _Tp> static
inline void elbp_(InputArray _src, OutputArray _dst, int radius, int neighbors) {
    //get matrices
    Mat src = _src.getMat();
    // allocate memory for result
    _dst.create(src.rows-2*radius, src.cols-2*radius, CV_32SC1);
    Mat dst = _dst.getMat();
    // zero
    dst.setTo(0);
    for(int n=0; n<neighbors; n++) {
        // sample points
        float x = static_cast<float>(-radius) * sin(2.0*CV_PI*n/static_cast<float>(neighbors));
        float y = static_cast<float>(radius) * cos(2.0*CV_PI*n/static_cast<float>(neighbors));
        // relative indices
        int fx = static_cast<int>(floor(x));
        int fy = static_cast<int>(floor(y));
        int cx = static_cast<int>(ceil(x));
        int cy = static_cast<int>(ceil(y));
        // fractional part
        float ty = y - fy;
        float tx = x - fx;
        // set interpolation weights
        float w1 = (1 - tx) * (1 - ty);
        float w2 =      tx  * (1 - ty);
        float w3 = (1 - tx) *      ty;
        float w4 =      tx  *      ty;
        // iterate through your data
        for(int i=radius; i < src.rows-radius;i++) {
            for(int j=radius;j < src.cols-radius;j++) {
                // calculate interpolated value
                float t = w1*src.at<_Tp>(i+fy,j+fx) + w2*src.at<_Tp>(i+fy,j+cx) + w3*src.at<_Tp>(i+cy,j+fx) + w4*src.at<_Tp>(i+cy,j+cx);
                // floating point precision, so check some machine-dependent epsilon
                dst.at<int>(i-radius,j-radius) += ((t > src.at<_Tp>(i,j)) || (std::abs(t-src.at<_Tp>(i,j)) < std::numeric_limits<float>::epsilon())) << n;
            }
        }
    }
}

static void elbp(InputArray src, OutputArray dst, int radius, int neighbors)
{
    switch (src.type()) {
        case CV_8SC1:   elbp_<char>(src,dst, radius, neighbors); break;
        case CV_8UC1:   elbp_<unsigned char>(src, dst, radius, neighbors); break;
        case CV_16SC1:  elbp_<short>(src,dst, radius, neighbors); break;
        case CV_16UC1:  elbp_<unsigned short>(src,dst, radius, neighbors); break;
        case CV_32SC1:  elbp_<int>(src,dst, radius, neighbors); break;
        case CV_32FC1:  elbp_<float>(src,dst, radius, neighbors); break;
        case CV_64FC1:  elbp_<double>(src,dst, radius, neighbors); break;
        default: break;
    }
}

static Mat
histc_(const Mat& src, int minVal=0, int maxVal=255, bool normed=false)
{
    Mat result;
    // Establish the number of bins.
    int histSize = maxVal-minVal+1;
    // Set the ranges.
    float range[] = { minVal, maxVal } ;
    const float* histRange = { range };
    // calc histogram
    calcHist(&src, 1, 0, Mat(), result, 1, &histSize, &histRange, true, false);
    // normalize
    if(normed) {
        result /= src.total();
    }
    return result.reshape(1,1);
}

static Mat histc(InputArray _src, int minVal, int maxVal, bool normed)
{
    Mat src = _src.getMat();
    switch (src.type()) {
        case CV_8SC1:
            return histc_(Mat_<float>(src), minVal, maxVal, normed);
            break;
        case CV_8UC1:
            return histc_(src, minVal, maxVal, normed);
            break;
        case CV_16SC1:
            return histc_(Mat_<float>(src), minVal, maxVal, normed);
            break;
        case CV_16UC1:
            return histc_(src, minVal, maxVal, normed);
            break;
        case CV_32SC1:
            return histc_(Mat_<float>(src), minVal, maxVal, normed);
            break;
        case CV_32FC1:
            return histc_(src, minVal, maxVal, normed);
            break;
        default:
            CV_Error(CV_StsUnmatchedFormats, "This type is not implemented yet."); break;
    }
    return Mat();
}

    
static Mat spatial_histogram(InputArray _src, int numPatterns,
                             int grid_x, int grid_y, bool normed)
{
    Mat src = _src.getMat();
    // calculate LBP patch size
    int width = static_cast<int>(floor(src.cols/grid_x));
    int height = static_cast<int>(floor(src.rows/grid_y));
    // allocate memory for the spatial histogram
    Mat result = Mat::zeros(grid_x * grid_y, numPatterns, CV_32FC1);
    // return matrix with zeros if no data was given
    if(src.empty())
        return result.reshape(1,1);
    // initial result_row
    int resultRowIdx = 0;
    // iterate through grid
    for(int i = 0; i < grid_y; i++) {
        for(int j = 0; j < grid_x; j++) {
            Mat src_cell = Mat(src, Range(i*height,(i+1)*height), Range(j*width,(j+1)*width));
            Mat cell_hist = histc(src_cell, 0, (numPatterns-1), true);
            // copy to the result matrix
            Mat result_row = result.row(resultRowIdx);
            cell_hist.reshape(1,1).convertTo(result_row, CV_32FC1);
            // increase row count in result matrix
            resultRowIdx++;
        }
    }
    // return result as reshaped feature vector
    return result.reshape(1,1);
}

//------------------------------------------------------------------------------
// cv::elbp, cv::olbp, cv::varlbp wrapper
//------------------------------------------------------------------------------

static Mat elbp(InputArray src, int radius, int neighbors) {
    Mat dst;
    elbp(src, dst, radius, neighbors);
    return dst;
}
    
void LBPH::load(const FileStorage& fs) {
    fs["radius"] >> _radius;
    fs["neighbors"] >> _neighbors;
    fs["grid_x"] >> _grid_x;
    fs["grid_y"] >> _grid_y;
    //read matrices
    readFileNodeList(fs["histograms"], _histograms);
    readFileNodeList(fs["labels"], _labels);
}

// See FaceRecognizer::save.
void LBPH::save(FileStorage& fs) const {
    fs << "radius" << _radius;
    fs << "neighbors" << _neighbors;
    fs << "grid_x" << _grid_x;
    fs << "grid_y" << _grid_y;
    // write matrices
    writeFileNodeList(fs, "histograms", _histograms);
    writeFileNodeList(fs, "labels", _labels);
}

void LBPH::train(InputArray _src, InputArray _lbls) {
    if(_src.kind() != _InputArray::STD_VECTOR_MAT && _src.kind() != _InputArray::STD_VECTOR_VECTOR)
        CV_Error(CV_StsUnsupportedFormat, "LBPH::train expects InputArray::STD_VECTOR_MAT or _InputArray::STD_VECTOR_VECTOR.");
    // get the vector of matrices
    vector<Mat> src;
    _src.getMatVector(src);
    // turn the label matrix into a vector
    vector<int> labels = _lbls.getMat();
    if(labels.size() != src.size())
        CV_Error(CV_StsUnsupportedFormat, "The number of labels must equal the number of samples.");
    // store given labels
    _labels = labels;
    // store the spatial histograms of the original data
    for(int sampleIdx = 0; sampleIdx < src.size(); sampleIdx++) {
        // calculate lbp image
        Mat lbp_image = elbp(src[sampleIdx], _radius, _neighbors);
        // get spatial histogram from this lbp image
        Mat p = spatial_histogram(
                lbp_image, /* lbp_image */
                static_cast<int>(std::pow(2.0, static_cast<double>(_neighbors))), /* number of possible patterns */
                _grid_x, /* grid size x */
                _grid_y, /* grid size y */
                true);
        // add to templates
        _histograms.push_back(p);
    }
}


int LBPH::predict(InputArray _src) const {
    Mat src = _src.getMat();
    // get the spatial histogram from input image
    Mat lbp_image = elbp(src, _radius, _neighbors);
    Mat query = spatial_histogram(
            lbp_image, /* lbp_image */
            static_cast<int>(std::pow(2.0, static_cast<double>(_neighbors))), /* number of possible patterns */
            _grid_x, /* grid size x */
            _grid_y, /* grid size y */
            true /* normed histograms */);
    // find 1-nearest neighbor
    double minDist = DBL_MAX;
    int minClass = -1;
    for(int sampleIdx = 0; sampleIdx < _histograms.size(); sampleIdx++) {
        double dist = compareHist(_histograms[sampleIdx], query, CV_COMP_CHISQR);
        if(dist < minDist) {
            minDist = dist;
            minClass = _labels[sampleIdx];
        }
    }
    return minClass;
}
    
    
Ptr<FaceRecognizer> createEigenFaceRecognizer(int num_components)
{
    return new Eigenfaces(num_components);
}
    
Ptr<FaceRecognizer> createFisherFaceRecognizer(int num_components)
{
    return new Fisherfaces(num_components);
}
    
Ptr<FaceRecognizer> createLBPHFaceRecognizer(int radius, int neighbors,
                                             int grid_x, int grid_y)
{
    return new LBPH(radius, neighbors, grid_x, grid_y);
}

}