opencv7-ml之KNN

准备知识

在文件”opencv\sources\modules\ml\src\precomp.hpp“中

有cvPrepareTrainData的函数原型。

int
cvPrepareTrainData( const char* /*funcname*/,
                    const CvMat* train_data, int tflag,
                    const CvMat* responses, int response_type,
                    const CvMat* var_idx,
                    const CvMat* sample_idx,
                    bool always_copy_data,
                    const float*** out_train_samples,
                    int* _sample_count,
                    int* _var_count,
                    int* _var_all,
                    CvMat** out_responses,
                    CvMat** out_response_map,
                    CvMat** out_var_idx,
                    CvMat** out_sample_idx=0 )

从函数原型的参数可以看出主要为：

const char* /funcname/： 函数的名称

const CvMat* train_data, int tflag,： 训练集、训练集样本的布局

const CvMat* responses, int response_type,：训练集标签、对应数据类型

const CvMat* var_idx,： 用了哪些特征

const CvMat* sample_idx,： 用了哪些样本

bool always_copy_data,： 是否复制数据集

const float*** out_train_samples,： 输出处理过的的训练集

int* _sample_count, ： 样本的总数

int* _var_count,： 特征的总数

int* _var_all,

CvMat** out_responses,： 输出训练集标签

CvMat** out_response_map,

CvMat** out_var_idx, ： 输出用了哪些特征

CvMat** out_sample_idx=0 ： 默认输出为使用了所有的样本

在文件”opencv\sources\modules\ml\src\inner_functions.cpp“中有cvPrepareTrainData的函数实现：

int
cvPrepareTrainData( const char* /*funcname*/,
                    const CvMat* train_data, int tflag,
                    const CvMat* responses, int response_type,
                    const CvMat* var_idx,
                    const CvMat* sample_idx,
                    bool always_copy_data,
                    const float*** out_train_samples,
                    int* _sample_count,
                    int* _var_count,
                    int* _var_all,
                    CvMat** out_responses,
                    CvMat** out_response_map,
                    CvMat** out_var_idx,
                    CvMat** out_sample_idx )
{
    int ok = 0;//用于标记该函数是否成功执行
    CvMat* _var_idx = 0;//默认使用所有的特征
    CvMat* _sample_idx = 0;//默认使用所有的样本
    CvMat* _responses = 0;
    int sample_all = 0, sample_count = 0, var_all = 0, var_count = 0;

    CV_FUNCNAME( "cvPrepareTrainData" );

    // step 0. clear all the output pointers to ensure we do not try
    // to call free() with uninitialized pointers
    //第0步，先释放所有输出的指针以确保不会有未初始化的指针。
    if( out_responses )
        *out_responses = 0;

    if( out_response_map )
        *out_response_map = 0;

    if( out_var_idx )
        *out_var_idx = 0;

    if( out_sample_idx )
        *out_sample_idx = 0;

    if( out_train_samples )
        *out_train_samples = 0;

    if( _sample_count )
        *_sample_count = 0;

    if( _var_count )
        *_var_count = 0;

    if( _var_all )
        *_var_all = 0;
//重置完成
    __BEGIN__;

    if( !out_train_samples )
        CV_ERROR( CV_StsBadArg, "output pointer to train samples is NULL" );

    CV_CALL( cvCheckTrainData( train_data, tflag, 0, &var_all, &sample_all ));

    if( sample_idx )
        CV_CALL( _sample_idx = cvPreprocessIndexArray( sample_idx, sample_all ));
    if( var_idx )
        CV_CALL( _var_idx = cvPreprocessIndexArray( var_idx, var_all ));

    if( responses )
    {
        if( !out_responses )
            CV_ERROR( CV_StsNullPtr, "output response pointer is NULL" );

        if( response_type == CV_VAR_NUMERICAL )
        {
            CV_CALL( _responses = cvPreprocessOrderedResponses( responses,
                                                _sample_idx, sample_all ));
        }
        else
        {
            CV_CALL( _responses = cvPreprocessCategoricalResponses( responses,
                                _sample_idx, sample_all, out_response_map, 0 ));
        }
    }

    CV_CALL( *out_train_samples =
                cvGetTrainSamples( train_data, tflag, _var_idx, _sample_idx,
                                   &var_count, &sample_count, always_copy_data ));

    ok = 1;

    __END__;
//如果上面的操作都结束了，那么检测对应的输出需要的指针，是否已经初始化，然后接着对各自的输出指针指向的对象进行置0初始化
    if( ok )
    {
        if( out_responses )
            *out_responses = _responses, _responses = 0;

        if( out_var_idx )
            *out_var_idx = _var_idx, _var_idx = 0;

        if( out_sample_idx )
            *out_sample_idx = _sample_idx, _sample_idx = 0;

        if( _sample_count )
            *_sample_count = sample_count;

        if( _var_count )
            *_var_count = var_count;

        if( _var_all )
            *_var_all = var_all;
    }
    else
    {
        if( out_response_map )
            cvReleaseMat( out_response_map );
        cvFree( out_train_samples );
    }

    if( _responses != responses )
        cvReleaseMat( &_responses );
    cvReleaseMat( &_var_idx );
    cvReleaseMat( &_sample_idx );

    return ok;//返回该函数是否成功执行
}

首先在文件“opencv\sources\modules\ml\include\opencv2\ml\ml.hpp”中有：

#define CV_TYPE_NAME_ML_KNN     "opencv-ml-knn"
struct CvVectors
{
    int type;
    int dims, count;
    CvVectors* next;
    union
    {
        uchar** ptr;
        float** fl;
        double** db;
    } data;
}；

/*********K-Nearest Neighbour Classifier **********/

class CV_EXPORTS_W CvKNearest : public CvStatModel
{
public:

    CV_WRAP CvKNearest();//默认构造函数
    virtual ~CvKNearest();//虚析构函数
//2个重载的构造函数，参数中一个是CvMat，一个是Mat
//trainData:训练集
//responses:训练集的目标值
//sampleIdx：用来指定使用哪些训练样本，0表示使用所有的训练样本
//isRegression：trueb表示knn作为回归，否则为分类器
//max_k：K的上限
    CvKNearest( const CvMat* trainData, const CvMat* responses,
                const CvMat* sampleIdx=0, bool isRegression=false, int max_k=32 );

    CV_WRAP CvKNearest( const cv::Mat& trainData, const cv::Mat& responses,
               const cv::Mat& sampleIdx=cv::Mat(), bool isRegression=false, int max_k=32 );
//训练模型，两个重载函数，一个使用的是CvMat；一个使用的是Mat；Mat的会调用CvMat的train实现训练功能。
//updateBase:用于指定该模型是从头开始训练？(update_base=false)，还是使用新的训练数据来进行更新
//(update_base=true).在后者中，参数maxK不能大于原始的值
         virtual bool train( const CvMat* trainData, const CvMat* responses,
                        const CvMat* sampleIdx=0, bool is_regression=false,
                        int maxK=32, bool updateBase=false );

    CV_WRAP virtual bool train( const cv::Mat& trainData, const cv::Mat& responses,
                       const cv::Mat& sampleIdx=cv::Mat(), bool isRegression=false,
                       int maxK=32, bool updateBase=false );
//寻找邻居 然后预测输入向量的目标：3个重载函数
   virtual float find_nearest( const CvMat* samples, int k, CV_OUT CvMat* results=0,
        const float** neighbors=0, CV_OUT CvMat* neighborResponses=0, CV_OUT CvMat* dist=0 ) const;

    virtual float find_nearest( const cv::Mat& samples, int k, cv::Mat* results=0,
                                const float** neighbors=0, cv::Mat* neighborResponses=0,
                                cv::Mat* dist=0 ) const;

    CV_WRAP virtual float find_nearest( const cv::Mat& samples, int k, CV_OUT cv::Mat& results,
                                        CV_OUT cv::Mat& neighborResponses, CV_OUT cv::Mat& dists) const;
//
        virtual void find_neighbors_direct( const CvMat* _samples, int k, int start, int end,
        float* neighbor_responses, const float** neighbors, float* dist ) const;

    virtual void clear();
    int get_max_k() const;//返回近邻中最大值的个数
    int get_var_count() const;//返回特征的维度（变量的个数）
    int get_sample_count() const;//返回训练样本的个数
    bool is_regression() const;//返回的true为回归；false为分类
//将结果记录下来
    virtual float write_results( int k, int k1, int start, int end,
        const float* neighbor_responses, const float* dist, CvMat* _results,
        CvMat* _neighbor_responses, CvMat* _dist, Cv32suf* sort_buf ) const;

protected:

    int max_k, var_count;//最大的k值；特征维度
    int total;//
    bool regression;//是否是回归
    CvVectors* samples;//样本向量
};

typedef CvKNearest KNearest;

对于该文件的实现和上面的类定义一样，为了兼容opencv1.0版本，所以之前的CvMat都是1.0的形式；而在后面Mat的都是opencv2.0的形式。

下面是文件“\opencv\sources\modules\ml\src\knearest.cpp”中实现部分：

#include "precomp.hpp"

/********K-Nearest Neighbors Classifier ***********/
//1、opencv1.0形式
// k Nearest Neighbors
//默认构造函数
CvKNearest::CvKNearest()
{
    samples = 0;//指针初始化
    clear();
}

//析构函数
CvKNearest::~CvKNearest()
{
    clear();//调用清除函数,该函数在下面
}

//构造函数
//_train_data:训练集合，行为样本，列为特征
// _responses：训练集合对应的类别目标

CvKNearest::CvKNearest( const CvMat* _train_data, const CvMat* _responses,
                        const CvMat* _sample_idx, bool _is_regression, int _max_k )
{
    samples = 0;//指针赋值为0
    //调用类成员函数train来训练模型
    train( _train_data, _responses, _sample_idx, _is_regression, _max_k, false );
}

void CvKNearest::clear()
{
//类似释放链表一样释放所有的样本
    while( samples )
    {
        CvVectors* next_samples = samples->next;
        cvFree( &samples->data.fl );
        cvFree( &samples );
        samples = next_samples;
    }
    //将对应的类成员置0
    var_count = 0;
    total = 0;
    max_k = 0;
}

//返回类成员max_k，表示K的最大上限
int CvKNearest::get_max_k() const { return max_k; }
//返回样本的特征维度
int CvKNearest::get_var_count() const { return var_count; }
//返回当前knn作为分类器，还是用来做回归
bool CvKNearest::is_regression() const { return regression; }
//返回训练集的样本总数
int CvKNearest::get_sample_count() const { return total; }

//模型训练函数。主要是对训练数据进行排序，然后采用合适的数据结构来存储数据集。
bool CvKNearest::train( const CvMat* _train_data, const CvMat* _responses,
                        const CvMat* _sample_idx, bool _is_regression,
                        int _max_k, bool _update_base )
{
    bool ok = false;//用来标记该train函数是否成功执行
    CvMat* responses = 0;

    CV_FUNCNAME( "CvKNearest::train" );

    __BEGIN__;

    CvVectors* _samples = 0;
    float** _data = 0;
    int _count = 0, _dims = 0, _dims_all = 0, _rsize = 0;

    if( !_update_base )
        clear();

    // Prepare training data and related parameters.
    //准备好数据和对应的参数
    // Treat categorical responses as ordered - to prevent class label compression and
    // to enable entering new classes in the updates
  //让类别的目标有序，这样能够防止类别标签被压缩并且能够可以在更新中加入新的类 。该工作通过调用cvPrepareTrainData函数来完成
    CV_CALL( cvPrepareTrainData( "CvKNearest::train", _train_data, CV_ROW_SAMPLE,
        _responses, CV_VAR_ORDERED, 0, _sample_idx, true, (const float***)&_data,
        &_count, &_dims, &_dims_all, &responses, 0, 0 ));

    if( !responses )
        CV_ERROR( CV_StsNoMem, "Could not allocate memory for responses" );

    if( _update_base && _dims != var_count )
        CV_ERROR( CV_StsBadArg, "The newly added data have different dimensionality" );

    if( !_update_base )
    {
    //如果用户设定的k小于1，那么报错
        if( _max_k < 1 )
            CV_ERROR( CV_StsOutOfRange, "max_k must be a positive number" );

        regression = _is_regression;//是否用作回归
        var_count = _dims;//特征的维度
        max_k = _max_k;//k的上限
    }

    _rsize = _count*sizeof(float);

    _samples->next = samples;
    _samples->type = CV_32F;
    _samples->data.fl = _data;
    _samples->count = _count;
    total += _count;

    samples = _samples;
    memcpy( _samples + 1, responses->data.fl, _rsize );

    ok = true;

    __END__;

    if( responses && responses->data.ptr != _responses->data.ptr )
        cvReleaseMat(&responses);

    return ok;
}

void CvKNearest::find_neighbors_direct( const CvMat* _samples, int k, int start, int end,
                    float* neighbor_responses, const float** neighbors, float* dist ) const
{
    int i, j, count = end - start, k1 = 0, k2 = 0, d = var_count;
    CvVectors* s = samples;

    for( ; s != 0; s = s->next )
    {
        int n = s->count;
        for( j = 0; j < n; j++ )
        {
            for( i = 0; i < count; i++ )
            {
                double sum = 0;
                Cv32suf si;
                const float* v = s->data.fl[j];
                const float* u = (float*)(_samples->data.ptr + _samples->step*(start + i));
                Cv32suf* dd = (Cv32suf*)(dist + i*k);
                float* nr;
                const float** nn;
                int t, ii, ii1;

                for( t = 0; t <= d - 4; t += 4 )
                {
                    double t0 = u[t] - v[t], t1 = u[t+1] - v[t+1];
                    double t2 = u[t+2] - v[t+2], t3 = u[t+3] - v[t+3];
                    sum += t0*t0 + t1*t1 + t2*t2 + t3*t3;
                }

                for( ; t < d; t++ )
                {
                    double t0 = u[t] - v[t];
                    sum += t0*t0;
                }

                si.f = (float)sum;
                for( ii = k1-1; ii >= 0; ii-- )
                    if( si.i > dd[ii].i )
                        break;
                if( ii >= k-1 )
                    continue;

                nr = neighbor_responses + i*k;
                nn = neighbors ? neighbors + (start + i)*k : 0;
                for( ii1 = k2 - 1; ii1 > ii; ii1-- )
                {
                    dd[ii1+1].i = dd[ii1].i;
                    nr[ii1+1] = nr[ii1];
                    if( nn ) nn[ii1+1] = nn[ii1];
                }
                dd[ii+1].i = si.i;
                nr[ii+1] = ((float*)(s + 1))[j];
                if( nn )
                    nn[ii+1] = v;
            }
            k1 = MIN( k1+1, k );
            k2 = MIN( k1, k-1 );
        }
    }
}

float CvKNearest::write_results( int k, int k1, int start, int end,
    const float* neighbor_responses, const float* dist,
    CvMat* _results, CvMat* _neighbor_responses,
    CvMat* _dist, Cv32suf* sort_buf ) const
{
    float result = 0.f;
    int i, j, j1, count = end - start;
    double inv_scale = 1./k1;
    int rstep = _results && !CV_IS_MAT_CONT(_results->type) ? _results->step/sizeof(result) : 1;

    for( i = 0; i < count; i++ )
    {
        const Cv32suf* nr = (const Cv32suf*)(neighbor_responses + i*k);
        float* dst;
        float r;
        if( _results || start+i == 0 )
        {
            if( regression )
            {
                double s = 0;
                for( j = 0; j < k1; j++ )
                    s += nr[j].f;
                r = (float)(s*inv_scale);
            }
            else
            {
                int prev_start = 0, best_count = 0, cur_count;
                Cv32suf best_val;

                for( j = 0; j < k1; j++ )
                    sort_buf[j].i = nr[j].i;

                for( j = k1-1; j > 0; j-- )
                {
                    bool swap_fl = false;
                    for( j1 = 0; j1 < j; j1++ )
                        if( sort_buf[j1].i > sort_buf[j1+1].i )
                        {
                            int t;
                            CV_SWAP( sort_buf[j1].i, sort_buf[j1+1].i, t );
                            swap_fl = true;
                        }
                    if( !swap_fl )
                        break;
                }

                best_val.i = 0;
                for( j = 1; j <= k1; j++ )
                    if( j == k1 || sort_buf[j].i != sort_buf[j-1].i )
                    {
                        cur_count = j - prev_start;
                        if( best_count < cur_count )
                        {
                            best_count = cur_count;
                            best_val.i = sort_buf[j-1].i;
                        }
                        prev_start = j;
                    }
                r = best_val.f;
            }

            if( start+i == 0 )
                result = r;

            if( _results )
                _results->data.fl[(start + i)*rstep] = r;
        }

        if( _neighbor_responses )
        {
            dst = (float*)(_neighbor_responses->data.ptr +
                (start + i)*_neighbor_responses->step);
            for( j = 0; j < k1; j++ )
                dst[j] = nr[j].f;
            for( ; j < k; j++ )
                dst[j] = 0.f;
        }

        if( _dist )
        {
            dst = (float*)(_dist->data.ptr + (start + i)*_dist->step);
            for( j = 0; j < k1; j++ )
                dst[j] = dist[j + i*k];
            for( ; j < k; j++ )
                dst[j] = 0.f;
        }
    }

    return result;
}

struct P1 : cv::ParallelLoopBody {
  P1(const CvKNearest* _pointer, int _buf_sz, int _k, const CvMat* __samples, const float** __neighbors,
     int _k1, CvMat* __results, CvMat* __neighbor_responses, CvMat* __dist, float* _result)
  {
    pointer = _pointer;
    k = _k;
    _samples = __samples;
    _neighbors = __neighbors;
    k1 = _k1;
    _results = __results;
    _neighbor_responses = __neighbor_responses;
    _dist = __dist;
    result = _result;
    buf_sz = _buf_sz;
  }

  const CvKNearest* pointer;
  int k;
  const CvMat* _samples;
  const float** _neighbors;
  int k1;
  CvMat* _results;
  CvMat* _neighbor_responses;
  CvMat* _dist;
  float* result;
  int buf_sz;

  void operator()( const cv::Range& range ) const
  {
    cv::AutoBuffer<float> buf(buf_sz);
    for(int i = range.start; i < range.end; i += 1 )
    {
        float* neighbor_responses = &buf[0];
        float* dist = neighbor_responses + 1*k;
        Cv32suf* sort_buf = (Cv32suf*)(dist + 1*k);

        pointer->find_neighbors_direct( _samples, k, i, i + 1,
                    neighbor_responses, _neighbors, dist );

        float r = pointer->write_results( k, k1, i, i + 1, neighbor_responses, dist,
                                 _results, _neighbor_responses, _dist, sort_buf );

        if( i == 0 )
            *result = r;
    }
  }

};
//对每个输入向量（表示为_sample矩阵的每一行），该方法找到k（k≤get_max_k() ）个最近邻。
//在回归中，预测结果将是响应的近邻向量的均值。在分类中，通过投票决定类别结果。

//对传统分类和回归预测来说，该方法可以有选择的返回近邻向量本身的指针
//(neighbors, array of k*_samples->rows pointers)，
//它们相对应的输出值(neighbor_responses, a vector of k*_samples->rows elements) ，
//和输入向量与近邻之间的距离(dist, also a vector of k*_samples->rows elements)。

//对每个输入向量来说，近邻将按照它们到该向量的距离排序。

//对单个输入向量，所有的输出矩阵是可选的，而且预测值将由该方法返回。
float CvKNearest::find_nearest( const CvMat* _samples, int k, CvMat* _results,
    const float** _neighbors, CvMat* _neighbor_responses, CvMat* _dist ) const
{
    float result = 0.f;
    const int max_blk_count = 128, max_buf_sz = 1 << 12;

    if( !samples )
        CV_Error( CV_StsError, "The search tree must be constructed first using train method" );

    if( !CV_IS_MAT(_samples) ||
        CV_MAT_TYPE(_samples->type) != CV_32FC1 ||
        _samples->cols != var_count )
        CV_Error( CV_StsBadArg, "Input samples must be floating-point matrix (<num_samples>x<var_count>)" );

    if( _results && (!CV_IS_MAT(_results) ||
        (_results->cols != 1 && _results->rows != 1) ||
        _results->cols + _results->rows - 1 != _samples->rows) )
        CV_Error( CV_StsBadArg,
        "The results must be 1d vector containing as much elements as the number of samples" );

    if( _results && CV_MAT_TYPE(_results->type) != CV_32FC1 &&
        (CV_MAT_TYPE(_results->type) != CV_32SC1 || regression))
        CV_Error( CV_StsUnsupportedFormat,
        "The results must be floating-point or integer (in case of classification) vector" );

    if( k < 1 || k > max_k )
        CV_Error( CV_StsOutOfRange, "k must be within 1..max_k range" );

    if( _neighbor_responses )
    {
        if( !CV_IS_MAT(_neighbor_responses) || CV_MAT_TYPE(_neighbor_responses->type) != CV_32FC1 ||
            _neighbor_responses->rows != _samples->rows || _neighbor_responses->cols != k )
            CV_Error( CV_StsBadArg,
            "The neighbor responses (if present) must be floating-point matrix of <num_samples> x <k> size" );
    }

    if( _dist )
    {
        if( !CV_IS_MAT(_dist) || CV_MAT_TYPE(_dist->type) != CV_32FC1 ||
            _dist->rows != _samples->rows || _dist->cols != k )
            CV_Error( CV_StsBadArg,
            "The distances from the neighbors (if present) must be floating-point matrix of <num_samples> x <k> size" );
    }

    int count = _samples->rows;
    int count_scale = k*2;
    int blk_count0 = MIN( count, max_blk_count );
    int buf_sz = MIN( blk_count0 * count_scale, max_buf_sz );
    blk_count0 = MAX( buf_sz/count_scale, 1 );
    blk_count0 += blk_count0 % 2;
    blk_count0 = MIN( blk_count0, count );
    buf_sz = blk_count0 * count_scale + k;
    int k1 = get_sample_count();
    k1 = MIN( k1, k );

    cv::parallel_for_(cv::Range(0, count), P1(this, buf_sz, k, _samples, _neighbors, k1,
                                             _results, _neighbor_responses, _dist, &result)
    );

    return result;
}

/////////////////////////////////////////////////////
//2、下面是采用opencv2.0的形式写的
using namespace cv;
//构造函数，参数为：训练数据；训练数据的目标值
//_train_data:行表示样本，列表示维度
CvKNearest::CvKNearest( const Mat& _train_data, const Mat& _responses,
                       const Mat& _sample_idx, bool _is_regression, int _max_k )
{
    samples = 0;
    //调用对应cpp版本的训练函数
    train(_train_data, _responses, _sample_idx, _is_regression, _max_k, false );
}
//训练模型
bool CvKNearest::train( const Mat& _train_data, const Mat& _responses,
                        const Mat& _sample_idx, bool _is_regression,
                        int _max_k, bool _update_base )
{
//将训练数据、训练数据的目标值、提取出来。然后调用opencv1。0版本的训练函数来训练。
    CvMat tdata = _train_data, responses = _responses, sidx = _sample_idx;

    return train(&tdata, &responses, sidx.data.ptr ? &sidx : 0, _is_regression, _max_k, _update_base );
}

//寻找最近邻
float CvKNearest::find_nearest( const Mat& _samples, int k, Mat* _results,
                                const float** _neighbors, Mat* _neighbor_responses,
                                Mat* _dist ) const
{
    CvMat s = _samples, results, *presults = 0, nresponses, *pnresponses = 0, dist, *pdist = 0;

    if( _results )
    {
        if(!(_results->data && (_results->type() == CV_32F ||
            (_results->type() == CV_32S && regression)) &&
             (_results->cols == 1 || _results->rows == 1) &&
             _results->cols + _results->rows - 1 == _samples.rows) )
            _results->create(_samples.rows, 1, CV_32F);
        presults = &(results = *_results);
    }

    if( _neighbor_responses )
    {
        if(!(_neighbor_responses->data && _neighbor_responses->type() == CV_32F &&
             _neighbor_responses->cols == k && _neighbor_responses->rows == _samples.rows) )
            _neighbor_responses->create(_samples.rows, k, CV_32F);
        pnresponses = &(nresponses = *_neighbor_responses);
    }

    if( _dist )
    {
        if(!(_dist->data && _dist->type() == CV_32F &&
             _dist->cols == k && _dist->rows == _samples.rows) )
            _dist->create(_samples.rows, k, CV_32F);
        pdist = &(dist = *_dist);
    }
//调用另一个寻找近邻的函数完成剩下的工作（即之前opencv1.0版本的那个函数）
    return find_nearest(&s, k, presults, _neighbors, pnresponses, pdist );
}

//寻找最近邻，该方法是传递引用
float CvKNearest::find_nearest( const cv::Mat& _samples, int k, CV_OUT cv::Mat& results,
                                CV_OUT cv::Mat& neighborResponses, CV_OUT cv::Mat& dists) const
{
//调用另一个寻找最近邻的函数实现（即上面那个函数）
    return find_nearest(_samples, k, &results, 0, &neighborResponses, &dists);
}

/* End of file */

例子：

#include "ml.h"
#include "highgui.h"
int main( int argc, char** argv ){
  const int K = 10;
  int i, j, k, accuracy;
  float response;
  int train_sample_count = 100;//100个训练样本
  CvRNG rng_state = cvRNG(-1);//随机数状态
  //建立训练集中的数据和类别标签
  CvMat* trainData = cvCreateMat( train_sample_count,
                                  2, CV_32FC1 );
  CvMat* trainClasses = cvCreateMat( train_sample_count,
                                     1, CV_32FC1 );
    //创建一张画布用来呈现结果
  IplImage* img = cvCreateImage( cvSize( 500, 500 ), 8, 3 );

  float _sample[2];

  CvMat sample = cvMat( 1, 2, CV_32FC1, _sample );

  cvZero( img );//对画布进行清零操作

  CvMat trainData1, trainData2, trainClasses1, trainClasses2;

// form the training samples
//将trainData中上部分提取出来，然后填充随机数
  cvGetRows( trainData, &trainData1, 0,   train_sample_count/2 );
  cvRandArr( &rng_state, &trainData1, CV_RAND_NORMAL,    cvScalar(200,200), cvScalar(50,50) );

  //将trainData下部分提取出来，填充随机数
  cvGetRows(trainData, &trainData2, train_sample_count / 2, train_sample_count);
  cvRandArr( &rng_state, &trainData2, CV_RAND_NORMAL,   cvScalar(300,300), cvScalar(50,50) );

//对于trainClasses的上半部分置为1，表示前50个都是第1类
  cvGetRows( trainClasses, &trainClasses1, 0, train_sample_count/2 );
cvSet( &trainClasses1, cvScalar(1) );

//对于trainClasses的下半部分置为2，表示后50个都是第2类
  cvGetRows( trainClasses, &trainClasses2, train_sample_count/2, train_sample_count )；
  cvSet( &trainClasses2, cvScalar(2) );

//训练knn用作分类
  CvKNearest knn( trainData, trainClasses, 0, false, K );
//建立一个K矩阵，用来存储K个最近邻
   CvMat* nearests = cvCreateMat( 1, K, CV_32FC1);
 //将画布上每个点都进行分类
  for( i = 0; i < img->height; i++ ){
    for( j = 0; j < img->width; j++ ){
      sample.data.fl[0] = (float)j;
      sample.data.fl[1] = (float)i;
// estimate the response and get the neighbors’ labels
//该函数返回该点的类别
      response = knn.find_nearest(&sample,K,0,0,nearests,0);
// compute the number of neighbors representing the majority
//计算这K个近邻中有多少是支持第response类的。即准确度
      for( k = 0, accuracy = 0; k < K; k++ ){
         if( nearests->data.fl[k] == response)
           accuracy++;
      }
// highlight the pixel depending on the accuracy (or confidence)
//按照不同的类别赋值不同的颜色，并根据准确度的多少赋值颜色的混合区域，即
//最后的结果的图中中间层就是有争议的部分。
  cvSet2D( img, i, j, response == 1 ?
(accuracy > 5 ? CV_RGB(180,0,0) : CV_RGB(180,120,0)) :
(accuracy > 5 ? CV_RGB(0,180,0) : CV_RGB(120,120,0)) );
    }
  }
// display the original training samples
//显示原始的100训练样本，用小点标记出来，以区分画布中的其他点
  for( i = 0; i < train_sample_count/2; i++ ){
    CvPoint pt;
    pt.x = cvRound(trainData1.data.fl[i*2]);
    pt.y = cvRound(trainData1.data.fl[i*2+1]);
    cvCircle( img, pt, 2, CV_RGB(255,0,0), CV_FILLED );
    pt.x = cvRound(trainData2.data.fl[i*2]);
    pt.y = cvRound(trainData2.data.fl[i*2+1]);
    cvCircle( img, pt, 2, CV_RGB(0,255,0), CV_FILLED );
  }
  //将结果呈现出来
  cvNamedWindow( "classifier result", 1 );
  cvShowImage( "classifier result", img );
  cvWaitKey(0);
  cvReleaseMat( &trainClasses );
  cvReleaseMat( &trainData );
  return 0;
}

上面例子的结果：

对应的使用了opencv2.0的形式写了与上面类似的代码：

#include "opencv2\ml\ml.hpp"
#include "opencv2\highgui\highgui.hpp"
#include<iostream>
using namespace std;
using namespace cv;
int main(int argc, char** argv){
    const int K = 10;
    int  accuracy=0;
    float response;
    int train_sample_count = 100;
    RNG rng;
    Mat trainData = Mat::zeros(100,2,CV_32FC1);
    Mat trainClasses = Mat::zeros(100, 1, CV_32FC1);

    Mat Image(Size2i(500, 500), CV_8UC3);
    Image.setTo(0);
    Mat sample(1, 2, CV_32FC1);

    Mat trainData1 = trainData(Range(0, train_sample_count / 2), Range::all());
    Mat trainData2 = trainData(Range(train_sample_count / 2, train_sample_count), Range::all());
    rng.fill(trainData1, RNG::UNIFORM, Scalar(50, 50), Scalar(200, 200));
    rng.fill(trainData2, RNG::UNIFORM, Scalar(200, 200), Scalar(300, 300));

    Mat trainClasses1 = trainClasses(Range(0, train_sample_count / 2),Range::all());
    Mat trainClasses2 = trainClasses(Range(train_sample_count / 2, train_sample_count), Range::all());
    trainClasses1.setTo(1);
    trainClasses2.setTo(2);

    KNearest Knn(trainData, trainClasses, Mat(), false, K);
    Mat nearests(1, K, CV_32FC1);

    Mat_<Vec3b> _I = Image;
    for (size_t i = 0; i < Image.rows; ++i){
        for (size_t j = 0; j < Image.cols; ++j) {
            sample.at<float>(0,0) = static_cast<float>(i);
            sample.at<float>(0,1) = static_cast<float>(j);

            response = Knn.find_nearest(sample, K);

            for (int k = 0, accuracy = 0; k < K; k++){
                    if (nearests.data[k] == response)
                                accuracy++;
            }

            response == 1 ?
                (accuracy > 5 ? (_I(i, j)[0] = 180,  _I(i, j)[1] = 0,    _I(i, j)[2]=0):
                                (_I(i, j)[0] = 180,  _I(i, j)[1] = 120,  _I(i, j)[2] = 0 )) :
                (accuracy > 5 ?  (_I(i, j)[0] = 0,   _I(i, j)[1] = 180,  _I(i, j)[2] = 0 ):
                                 (_I(i, j)[0] = 120, _I(i, j)[1] = 120,  _I(i, j)[2] = 0));
        }
    }
    Image = _I;

    for (int i = 0; i < train_sample_count / 2; i++){
        Point pt;

        pt.x = static_cast<int>(trainData1.at<float>(i, 0));
        pt.y = static_cast<int>(trainData1.at<float>(i, 1));
        circle(Image, pt, 1, Scalar(0, 0, 255),-1,8);

        pt.x = static_cast<int>(trainData2.at<float>(i, 0));
        pt.y = static_cast<int>(trainData2.at<float>(i, 1));
        circle(Image, pt, 1, Scalar(255, 0, 0), -1, 8);
    }

    namedWindow("result");
    imshow("result", Image);
    waitKey(0);
    cin.get();
    return 0;
}

生成的结果为：

上面的源码部分还未完全注释，待后续接着注释。

2015年09月27日，第0次修改！