我正在尝试基于HOG功能训练我自己的探测器，并且我使用opencv的CvSVM实用程序训练了一个探测器。现在在HOGDescriptor.SetSVM（myDetector）中使用此检测器，我需要以行向量（原始）形式获取训练的检测器以进行提供。为此我使用this代码。我的实现如下：
vector<float>primal;
void LinearSVM::getSupportVector(std::vector<float>& support_vector) {
CvSVM svm;
svm.load("Classifier.xml");
cin.get();
int sv_count = svm.get_support_vector_count();
const CvSVMDecisionFunc* df = decision_func;
const double* alphas = df[0].alpha;
double rho = df[0].rho;
int var_count = svm.get_var_count();
support_vector.resize(var_count, 0);
for (unsigned int r = 0; r < (unsigned)sv_count; r++) {
float myalpha = alphas[r];
const float* v = svm.get_support_vector(r);
for (int j = 0; j < var_count; j++,v++) {
support_vector[j] += (-myalpha) * (*v);
}
}
support_vector.push_back(rho);
}
int main()
{
LinearSVM s;
s.getSupportVector(primal);
return 0;
}
当我使用内置的CvSVM时，它显示SV为3因为我在保存的文件中只有3个SV，但由于decision_func处于保护模式，因此我无法访问它。这就是为什么我试图使用那个包装但仍然没用的原因。也许你们可以在这里帮助我......非常感谢！
答案 0 :(得分：0)
你好再次:)请扩展cvsm类而不是封装它，因为你需要访问受保护的成员。
//header
class mySVM : public CvSVM
{
public:
vector<float>
getWeightVector(const int descriptorSize);
};
//cpp
vector<float>
mySVM::getWeightVector(const int descriptorSize)
{
vector<float> svmWeightsVec(descriptorSize+1);
int numSupportVectors = get_support_vector_count();
//this is protected, but can access due to inheritance rules
const CvSVMDecisionFunc *dec = CvSVM::decision_func;
const float *supportVector;
float* svmWeight = &svmWeightsVec[0];
for (int i = 0; i < numSupportVectors; ++i)
{
float alpha = *(dec[0].alpha + i);
supportVector = get_support_vector(i);
for(int j=0;j<descriptorSize;j++)
{
*(svmWeight + j) += alpha * *(supportVector+j);
}
}
*(svmWeight + descriptorSize) = - dec[0].rho;
return svmWeightsVec;
}
类似的东西。
币： Obtaining weights in CvSVM, the SVM implementation of OpenCV
答案 1 :(得分：0)
用测试工具回答。我提出了新的答案，因为它会给原来的答案增加一些混乱，可能会让它有点混乱。
//dummy features
std:: vector<float>
dummyDerReaderForOneDer(const vector<float> &pattern)
{
int i = std::rand() % pattern.size();
int j = std::rand() % pattern.size();
vector<float> patternPulNoise(pattern);
std::random_shuffle(patternPulNoise.begin()+std::min(i,j),patternPulNoise.begin()+std::max(i,j));
return patternPulNoise;
};
//extend CvSVM to get access to weights
class mySVM : public CvSVM
{
public:
vector<float>
getWeightVector(const int descriptorSize);
};
//get the weights
vector<float>
mySVM::getWeightVector(const int descriptorSize)
{
vector<float> svmWeightsVec(descriptorSize+1);
int numSupportVectors = get_support_vector_count();
//this is protected, but can access due to inheritance rules
const CvSVMDecisionFunc *dec = CvSVM::decision_func;
const float *supportVector;
float* svmWeight = &svmWeightsVec[0];
for (int i = 0; i < numSupportVectors; ++i)
{
float alpha = *(dec[0].alpha + i);
supportVector = get_support_vector(i);
for(int j=0;j<descriptorSize;j++)
{
*(svmWeight + j) += alpha * *(supportVector+j);
}
}
*(svmWeight + descriptorSize) = - dec[0].rho;
return svmWeightsVec;
}
// main harness entry point for detector test
int main (int argc, const char * argv[])
{
//dummy variables for example
int posFiles = 10;
int negFiles = 10;
int dims = 1000;
int randomFactor = 4;
//setup some dummy data
vector<float> dummyPosPattern;
dummyPosPattern.assign(int(dims/randomFactor),1.f);
dummyPosPattern.resize(dims );
random_shuffle(dummyPosPattern.begin(),dummyPosPattern.end());
vector<float> dummyNegPattern;
dummyNegPattern.assign(int(dims/randomFactor),1.f);
dummyNegPattern.resize(dims );
random_shuffle(dummyNegPattern.begin(),dummyNegPattern.end());
// the labels and lables mat
float posLabel = 1.f;
float negLabel = 2.f;
cv::Mat cSvmLabels;
//the data mat
cv::Mat cSvmTrainingData;
//dummy linear svm parmas
SVMParams cSvmParams;
cSvmParams.svm_type = cv::SVM::C_SVC;
cSvmParams.C = 0.0100;
cSvmParams.kernel_type = cv::SVM::LINEAR;
cSvmParams.term_crit = cv::TermCriteria(CV_TERMCRIT_ITER+CV_TERMCRIT_EPS, 1000000, FLT_EPSILON);
cout << "creating training data. please wait" << endl;
int i;
for(i=0;i<posFiles;i++)
{
//your feature for one box from file
vector<float> d = dummyDerReaderForOneDer(dummyPosPattern);
//push back a new mat made from the vectors data, with copy data flag on
//this shows the format of the mat for a single example, (1 (row) X dims(col) ), as training mat has each **row** as an example;
//the push_back works like vector add adds each example to the bottom of the matrix
cSvmTrainingData.push_back(cv::Mat(1,dims,CV_32FC1,d.data(),true));
//push back a pos label to the labels mat
cSvmLabels.push_back(posLabel);
}
//do same with neg files;
for(i=0;i<negFiles;i++)
{
float a = rand();
vector<float> d = dummyDerReaderForOneDer(dummyNegPattern);
cSvmTrainingData.push_back(cv::Mat(1,dims,CV_32FC1,d.data(),true));
cSvmLabels.push_back(negLabel);
}
//have a look
cv::Mat viz;
cSvmTrainingData.convertTo(viz,CV_8UC3);
viz = viz*255;
cv::imshow("svmData", viz);
cv::waitKey(10);
cout << "press any key to continue" << endl;
getchar();
viz.release();
//create the svm;
cout << "training, please wait" << endl;
mySVM svm;
svm.train(cSvmTrainingData,cSvmLabels,cv::Mat(),cv::Mat(),cSvmParams);
cout << "get weights" << endl;
vector<float> svmWeights = svm.getWeightVector(dims);
for(i=0; i<dims+1; i++)
{
cout << svmWeights[i] << ", ";
if(i==dims)
{
cout << endl << "bias: " << svmWeights[i] << endl;
}
}
cout << "press any key to continue" << endl;
getchar();
cout << "testing, please wait" << endl;
//test the svm with a large amount of new unseen fake one at a time
int totExamples = 10;
int k;
for(i=0;i<totExamples; i++)
{
cout << endl << endl;
vector<float> dPos = dummyDerReaderForOneDer(dummyPosPattern);
cv::Mat dMatPos(1,dims,CV_32FC1,dPos.data(),true);
float predScoreFromDual = svm.predict(dMatPos,true);
float predScoreBFromPrimal = svmWeights[dims];
for( k = 0; k <= dims - 4; k += 4 )
predScoreBFromPrimal += dPos[k]*svmWeights[k] + dPos[k+1]*svmWeights[k+1] +
dPos[k+2]*svmWeights[k+2] + dPos[k+3]*svmWeights[k+3];
for( ; k < dims; k++ )
predScoreBFromPrimal += dPos[k]*svmWeights[k];
cout << "Dual Score:\t" << predScoreFromDual << "\tPrimal Score:\t" << predScoreBFromPrimal << endl;
}
cout << "press any key to continue" << endl;
getchar();
return(0);
}