Sunday, September 4, 2011

Histogram computation on a video

Histograms are collected counts of data organized into a set of predefined bins


 refracted class for histogram: given an input image, output the histogram image


class atsHistogram
{
public:
    cv::Mat DrawHistogram(Mat src)
    {
        /// Separate the image in 3 places ( R, G and B )
         vector<Mat> rgb_planes;
         split( src, rgb_planes );

         /// Establish the number of bins
         int histSize = 255;

         /// Set the ranges ( for R,G,B) )
         float range[] = { 0, 255 } ;
         const float* histRange = { range };

         bool uniform = true; bool accumulate = false;

         Mat r_hist, g_hist, b_hist;

         /// Compute the histograms:
         calcHist( &rgb_planes[0], 1, 0, Mat(), r_hist, 1, &histSize, &histRange, uniform, accumulate );
         calcHist( &rgb_planes[1], 1, 0, Mat(), g_hist, 1, &histSize, &histRange, uniform, accumulate );
         calcHist( &rgb_planes[2], 1, 0, Mat(), b_hist, 1, &histSize, &histRange, uniform, accumulate );

         // Draw the histograms for R, G and B
         int hist_w = 400; int hist_h = 400;
         int bin_w = cvRound( (double) hist_w/histSize );

         Mat histImage( hist_w, hist_h, CV_8UC3, Scalar( 0,0,0) );

         /// Normalize the result to [ 0, histImage.rows ]
         normalize(r_hist, r_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat() );
         normalize(g_hist, g_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat() );
         normalize(b_hist, b_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat() );

         /// Draw for each channel
         for( int i = 1; i < histSize; i++ )
           {
             line( histImage, Point( bin_w*(i-1), hist_h - cvRound(r_hist.at<float>(i-1)) ) ,
                              Point( bin_w*(i), hist_h - cvRound(r_hist.at<float>(i)) ),
                              Scalar( 0, 0, 255), 2, 8, 0  );
             line( histImage, Point( bin_w*(i-1), hist_h - cvRound(g_hist.at<float>(i-1)) ) ,
                              Point( bin_w*(i), hist_h - cvRound(g_hist.at<float>(i)) ),
                              Scalar( 0, 255, 0), 2, 8, 0  );
             line( histImage, Point( bin_w*(i-1), hist_h - cvRound(b_hist.at<float>(i-1)) ) ,
                              Point( bin_w*(i), hist_h - cvRound(b_hist.at<float>(i)) ),
                              Scalar( 255, 0, 0), 2, 8, 0  );
            }
         return histImage;
    }
private:
};





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