(OpenCV) Hue Histogram drawing and get value of RGB and bin count (example source code using calcHist in openCV)

This histogram drawing source code is referenced Sample code of CAMshift in opencv.

We usually use hue color in hsv to get color distribution, because hue is a little bit free from lighting than RGB model.

The source code is example of drawing rgb graph from hue histogram.

I try to drawing color graph from 2 channel histogram, for example hue, saturation, but I failed, I don't know that is impossible or not.

But 1 channel is possible, refer to this source code and fiagure.

If you want to know how to get histogram, refer to this page.

Thank you.

#include <  stdio.h>
#include <  iostream>
#include <  opencv2\opencv.hpp>

#ifdef _DEBUG        
#pragma comment(lib, "opencv_core247d.lib")
#pragma comment(lib, "opencv_imgproc247d.lib")   //MAT processing
#pragma comment(lib, "opencv_highgui247d.lib")
#pragma comment(lib, "opencv_core247.lib")
#pragma comment(lib, "opencv_imgproc247.lib")
#pragma comment(lib, "opencv_highgui247.lib")

using namespace cv;
using namespace std;

//get representative 3 color

int main()
 //read 2 images for histogram comparing
 Mat imgA;
 Mat imgA_mask;
 imgA = imread(".\\image1.jpg");
 imgA_mask = imread(".\\image1_mask.jpg", 0);

 imshow("img1", imgA);
 imshow("img1_mask", imgA_mask);

 //variables preparing
 int hbins = 30; 
 int channels[] = {0};
 int histSize[] = {hbins};
 float hranges[] = { 0, 180 };
 const float* ranges[] = { hranges}; 

 Mat patch_HSV;
 MatND HistA, HistB;

 //cal histogram & normalization
 cvtColor(imgA, patch_HSV, CV_BGR2HSV);
 calcHist( &patch_HSV, 1, channels,  imgA_mask, //MaskForHisto, // // do use mask
     HistA, 1, histSize, ranges,
     true, // the histogram is uniform
     false );
 normalize(HistA, HistA,  0, 255, CV_MINMAX);

 //Mat for drawing 
 Mat histimg = Mat::zeros(200, 320, CV_8UC3); 
 histimg = Scalar::all(0);
 int binW = histimg.cols / hbins;
 Mat buf(1, hbins, CV_8UC3);
 //Set RGB color
 for( int i = 0; i <  hbins; i++ )
  buf.at< Vec3b>(i) = Vec3b(saturate_cast< uchar>(i*180./hbins), 255, 255);
 cvtColor(buf, buf, CV_HSV2BGR);
 //drawing routine
 for( int i = 0; i <  hbins; i++ )
  int val = saturate_cast< int>(HistA.at< float>(i)*histimg.rows/255);
  rectangle( histimg, Point(i*binW,histimg.rows),
   Point((i+1)*binW,histimg.rows - val),
   Scalar(buf.at< Vec3b>(i)), -1, 8 );
  int r,g,b;
  b =  buf.at< Vec3b>(i)[0];
  g =  buf.at< Vec3b>(i)[1];
  r =  buf.at< Vec3b>(i)[2];

  //show bin and RGB value
  printf("[%d] r=%d, g=%d, b=%d , bins = %d \n",i , r, g, b, val);
 imshow( "Histogram", histimg );


 return 0;


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