C++ opencv Histogram

#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <iostream>
#include <stdio.h>

using namespace std;
using namespace cv;

int main(int argc, char** argv)
{
VideoCapture cap(0);
Mat frame, dst;
while (1)
{
cap >> frame;
/// Separate the image in 3 places ( B, G and R )
vector<Mat> bgr_planes;
split(frame, bgr_planes);

/// Establish the number of bins
int histSize = 256;

/// Set the ranges ( for B,G,R) )
float range[] = { 0, 256 };
const float* histRange = { range };

bool uniform = true; bool accumulate = false;

Mat b_hist, g_hist, r_hist;

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

// Draw the histograms for B, G and R
int hist_w = 512; int hist_h = 400;
int bin_w = cvRound((double)hist_w / histSize);

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

/// Normalize the result to [ 0, histImage.rows ]
normalize(b_hist, b_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat());
normalize(g_hist, g_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat());
normalize(r_hist, r_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(b_hist.at<float>(i - 1))),
Point(bin_w*(i), hist_h - cvRound(b_hist.at<float>(i))),
Scalar(255, 0, 0), 1, 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), 1, 8, 0);
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), 1, 8, 0);
}
if (waitKey(30) == 27)
break;
/// Display
namedWindow("calcHist Demo", CV_WINDOW_AUTOSIZE);
namedWindow("Video", CV_WINDOW_AUTOSIZE);
imshow("calcHist Demo", histImage);
imshow("Video", frame);
}
return 0;
}