HOG descriptor computation and visualization

at img_raw = imread("C:\\testimg.png", 1); // load as color image
 
resize(img_raw, img_raw, Size(64,128) );
 
Mat img;
cvtColor(img_raw, img, CV_RGB2GRAY);
 
 
HOGDescriptor d;
// Size(128,64), //winSize
// Size(16,16), //blocksize
// Size(8,8), //blockStride,
// Size(8,8), //cellSize,
// 9, //nbins,
// 0, //derivAper,
// -1, //winSigma,
// 0, //histogramNormType,
// 0.2, //L2HysThresh,
// 0 //gammal correction,
// //nlevels=64
//);
 
// void HOGDescriptor::compute(const Mat& img, vector<float>& descriptors,
// Size winStride, Size padding,
// const vector<Point>& locations) const
vector<float> descriptorsValues;
vector<Point> locations;
d.compute( img, descriptorsValues, Size(0,0), Size(0,0), locations);
 
cout << "HOG descriptor size is " << d.getDescriptorSize() << endl;
cout << "img dimensions: " << img.cols << " width x " << img.rows << "height" << endl;
cout << "Found " << descriptorsValues.size() << " descriptor values" << endl;
cout << "Nr of locations specified : " << locations.size() << endl;

link:  http://www.juergenwiki.de/work/wiki/doku.php?id=public%3ahog_descriptor_computation_and_visualization