title: Extracting HoG Features using OpenCV
body: <p>I am trying to extract features using OpenCV's HoG API, however I can't seem to find the API that allow me to do that.</p>
  
  <p>What I am trying to do is to extract features using HoG from all my dataset (a set number of positive and negative images), then train my own SVM.</p>
  
  <p>I peeked into HoG.cpp under OpenCV, and it didn't help. All the codes are buried within complexities and the need to cater for different hardwares (e.g. Intel's IPP)</p>
  
  <p>My question is:</p>
  
  <ol>
  <li>Is there any API from OpenCV that I can use to extract all those features / descriptors to be fed into a SVM ? If there's how can I use it to train my own SVM ?</li>
  <li>If there isn't, are there any existing libraries out there, which could accomplish the same thing ?</li>
  </ol>
  
  <p>So far, I am actually porting an existing library (http://hogprocessing.altervista.org/) from Processing (Java) to C++, but it's still very slow, with detection taking around at least 16 seconds</p>
  
  <p>Has anyone else successfully to extract HoG features, how did you go around it ? And do you have any open source codes which I could use ?</p>
  
  <p>Thanks in advance</p>