gistfile1.cpp

// entropy(hsv)
// it computes the histogram on a neighborhood
Features::VectImgType Features::Histogram (const VectUcharPointType& pt)
{
  VectImgType hist( 3, cv::Mat::zeros(256, 1, CV_8UC1) );

  for (VectUcharPointType::const_iterator it = pt.begin();
       it != pt.end();
       ++it )
    {
    const cv::Vec3b& pix = *it;

    for( int d = 0; d < 3; d++)
      {
      cv::Mat& tempHist = hist[d];

      uchar val = pix[d];
      tempHist.at<uchar>( val, static_cast<uchar>( 0 ) ) = tempHist.at<uchar>( val, static_cast<uchar>( 0 ) ) + static_cast<uchar>( 1 );
      }
    }

  return hist;
}
// it compute the entropy
cv::Vec3f Features::Entropy (const VectUcharPointType& pt, const VectImgType& hist)
{
  assert( !pt.empty() );

  size_t N = pt.size();
  const float invN = 1. / static_cast< float >( N );

  cv::Vec3f ent(0., 0., 0.);

  for( int d = 0; d < 3; d++)
    {
    const cv::Mat& Hist = hist[d];
    float entropy = 0.;

    for (size_t i = 0; i < N; i++ )
      {
      const float val = ( pt[i] )[d];
      const float p = static_cast<float>( Hist.at< uchar >( val, 0 ) ) * invN;

      if( p > 0. )
        {
        entropy -= p*log(p);
        }
      else
        {
        std::cout << "p = 0"<<std::endl;
        }
      }
    ent[d] = entropy;
    }
  return ent;
}