calcHist() usage for RGB histogram...?

edit

I think that it could be an answer how tou calcHist. I don't know how to make slice using opencv functions even using this post

#include "opencv2/video/tracking.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/videoio/videoio.hpp"
#include "opencv2/highgui/highgui.hpp"

#include <iostream>

using namespace cv;
using namespace std;



int main(int argc, char **argv)
{
#define NBBIN 256
Mat m=imread("f:/lib/opencv/samples/data/lena.jpg",CV_LOAD_IMAGE_ANYCOLOR);
vector<int> hManual(0xFFFFFF);
int scale[]={2,4,8};
 // My own histogram to check
for (int i=0;i<m.rows;i++)
    for (int j = 0; j < m.cols; j++)
    {
        Vec3b v=m.at<Vec3b>(j,i);
        hManual[v[0] / scale[0] +256*(v[1] / scale[1]) +65536*(v[2] / scale[2])]++;
    }
const int indCanaux[] = {0,1,2 };
Mat histo3d;
const int bins[] = { NBBIN / scale[0],NBBIN / scale[1],NBBIN/scale[2] };
float etenduI[2] = { 0,NBBIN };
float etenduJ[2] = { 0,NBBIN };
float etenduK[2] = { 0,NBBIN };
float *lEtendu[]={ etenduI,etenduJ,etenduK};

calcHist(&m,1, indCanaux,Mat(),histo3d,3,bins, (const float **)lEtendu,true,false);

Range rangesHisto[] = { Range(0,bins[0]), Range(0,bins[1]),Range(0,bins[2]) };
int nbManual=0,nb2dnz=0,nb3dnz=0,nbPb=0,nbPbBis=0;
float   max=0;
int nbPixel2d=0,nbPixel3d=0;
cout << "Size 0 = " << histo3d.size[0] << "\n";
cout << "Size 1 = " << histo3d.size[1] << "\n";
cout << "Size 2 = " << histo3d.size[2] << "\n";
for (int i = 0; i < bins[0]; i++)
{
    Mat coupe;
    rangesHisto[0] = cv::Range(i, i + 1);
    coupe = histo3d(rangesHisto).clone();
    if (i==0)
    {
        cout << "Size 0 = " << coupe.size[0] << "\n";
        cout << "Size 1 = " << coupe.size[1] << "\n";
        cout << "Size 2 = " << coupe.size[2] << "\n";
    }
    Mat histo2d(2, &(histo3d.size[1]), histo3d.type());
    coupe.copySize(histo2d);
    {
        for (int j = 0; j<bins[1]; j ++)
            for (int k = 0; k<bins[2]; k ++)
                if (histo3d.type()==CV_32S  )
                {
                    float h2d = histo2d.at<int>(j, i), h3d = histo3d.at<int>(k, j, i);
                    if (h2d > 0)
                        nb2dnz++;
                    if (h3d > 0)
                        nb3dnz++;
                    if (h3d>max)
                        max=h3d;
                    if (h3d != h2d)
                        nbPb++;
                    if (h3d!=hManual[i+j*256+k*65536])
                        nbPbBis++;
                    nbPixel3d += h3d;
                    nbPixel2d += h2d;
                }
                else
                    if (histo3d.type() == CV_32F  )
                    {
                        float h2d= histo2d.at<float>(j,k),h3d= histo3d.at<float>(i,j,k),hM= hManual[i + j * 256 + k * 65536];
                        if (h2d > 0)
                            nb2dnz++;
                        if (h3d > 0)
                            nb3dnz++;
                        if (h3d>max)
                            max = h3d;
                        if (h3d != h2d)
                            nbPb++;
                        if (abs(h3d-hM)>1)
                            nbPbBis++;
                        nbPixel3d += h3d;
                        nbPixel2d += h2d;
                    }
    }
}
cout<<"Using slice Voxel != 0 ==> "<< nb2dnz <<"\n"<<"Using histo3d Voxel !=0 ==> "<< nb3dnz <<"\n";
cout << "Using slice Voxel !=  Using histo3d Voxel ==> " << nbPb << "\n";
cout << "Using slice Voxel in histogram  ==> " << nbPixel2d << "\n";
cout << "Using  histo3d Voxel in histogram  ==> " << nbPixel3d << "\n";
cout << "Using histo3d Voxel!=manual  ==> " << nbPbBis << "\n";
cout<<"max = "<<max<<"\n";
int indPlan=0;
Mat plan(bins[0], bins[1],CV_32FC1);
for (int i = 0; i<bins[0]; i++)
    for (int j = 0; j<bins[1]; j++)
        plan.at<float>(i,j) = i/256.0;
imshow("Plane Histo", plan);
waitKey();
for (int i = 0; i<bins[0 ...