Example source code of extract HOG feature from images, save descriptor values to xml file, using opencv (using HOGDescriptor )

This example source code is to extract HOG feature from images.
And save descriptors to XML file.

The source code explain how to use HOGDescriptor function.



..
#include < stdio.h>
#include < opencv2\opencv.hpp>
//#include < opencv2\gpu\gpu.hpp>

using namespace cv;
using namespace std;


#ifdef _DEBUG        
#pragma comment(lib, "opencv_core247d.lib")         
#pragma comment(lib, "opencv_imgproc247d.lib")   //MAT processing        
#pragma comment(lib, "opencv_objdetect247d.lib") //HOGDescriptor
//#pragma comment(lib, "opencv_gpu247d.lib")        
//#pragma comment(lib, "opencv_features2d247d.lib")        
#pragma comment(lib, "opencv_highgui247d.lib")        
//#pragma comment(lib, "opencv_ml247d.lib")      
//#pragma comment(lib, "opencv_stitching247d.lib");      
//#pragma comment(lib, "opencv_nonfree247d.lib");      
  
#else        
#pragma comment(lib, "opencv_core247.lib")        
#pragma comment(lib, "opencv_imgproc247.lib")        
#pragma comment(lib, "opencv_objdetect247.lib")        
//#pragma comment(lib, "opencv_gpu247.lib")        
//#pragma comment(lib, "opencv_features2d247.lib")        
#pragma comment(lib, "opencv_highgui247.lib")        
//#pragma comment(lib, "opencv_ml247.lib")        
//#pragma comment(lib, "opencv_stitching247.lib");      
//#pragma comment(lib, "opencv_nonfree247.lib");      
#endif 


void main()
{
 //variables
 char FullFileName[100];
 char FirstFileName[100]="./images/upperbody";
 char SaveHogDesFileName[100] = "Positive.xml";
 int FileNum=96;

 vector< vector < float> > v_descriptorsValues;
 vector< vector < Point> > v_locations;


 for(int i=0; i< FileNum; ++i)
 {
  sprintf_s(FullFileName, "%s%d.png", FirstFileName, i+1);
  printf("%s\n", FullFileName);

  //read image file
  Mat img, img_gray;
  img = imread(FullFileName);
  
  //resizing
  resize(img, img, Size(64,48) ); //Size(64,48) ); //Size(32*2,16*2)); //Size(80,72) ); 
  //gray
  cvtColor(img, img_gray, CV_RGB2GRAY);

  //extract feature
  HOGDescriptor d( Size(32,16), Size(8,8), Size(4,4), Size(4,4), 9);
  vector< float> descriptorsValues;
  vector< Point> locations;
  d.compute( img_gray, descriptorsValues, Size(0,0), Size(0,0), locations);

  //printf("descriptor number =%d\n", descriptorsValues.size() );
  v_descriptorsValues.push_back( descriptorsValues );
  v_locations.push_back( locations );
  //show image
  imshow("origin", img);

  waitKey(5);
 }

 //refer to this address -> http://feelmare.blogspot.kr/2014/04/the-example-source-code-of-2d-vector.html
 //save to xml
 FileStorage hogXml(SaveHogDesFileName, FileStorage::WRITE); //FileStorage::READ
 //2d vector to Mat
 int row=v_descriptorsValues.size(), col=v_descriptorsValues[0].size();
 printf("col=%d, row=%d\n", row, col);
 Mat M(row,col,CV_32F);
 //save Mat to XML
 for(int i=0; i< row; ++i)  
  memcpy( &(M.data[col * i * sizeof(float) ]) ,v_descriptorsValues[i].data(),col*sizeof(float));
 //write xml
 write(hogXml, "Descriptor_of_images",  M);

 //write(hogXml, "Descriptor", v_descriptorsValues );
 //write(hogXml, "locations", v_locations );
 hogXml.release();

}
...


same with above code.
< gist code start>

< gist code end >


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