爲什麼在直方圖畫布上畫出直方圖用了減法

 /// 在直方圖畫布上畫出直方圖
 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  );
    }

後面畫出的直方圖線的原點是在左下方，而圖像的原點是在左上方，所以應該是做一個減法

————————囧  小白很辛苦，自學是個坑！