C++ opencv Back Projection

#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"

#include <iostream>

using namespace cv;
using namespace std;

/// Global Variables
Mat src; Mat hsv; Mat hue;
int bins = 25;

/// Function Headers
void Hist_and_Backproj(int, void*);

/** @function main */
int main(int argc, char** argv)
{
VideoCapture cap(0);
while (1)
{
cap >> src;
/// Transform it to HSV
cvtColor(src, hsv, CV_BGR2HSV);

/// Use only the Hue value
hue.create(hsv.size(), hsv.depth());
int ch[] = { 0, 0 };
mixChannels(&hsv, 1, &hue, 1, ch, 1);

/// Create Trackbar to enter the number of bins
char* window_image = "Source image";
namedWindow(window_image, CV_WINDOW_AUTOSIZE);
createTrackbar("* Hue  bins: ", window_image, &bins, 180, Hist_and_Backproj);
Hist_and_Backproj(0, 0);

/// Show the image
imshow(window_image, src);

if (waitKey(30) == 27)
break;
}
return 0;
}

void Hist_and_Backproj(int, void*)
{
MatND hist;
int histSize = MAX(bins, 2);
float hue_range[] = { 0, 180 };
const float* ranges = { hue_range };

/// Get the Histogram and normalize it
calcHist(&hue, 1, 0, Mat(), hist, 1, &histSize, &ranges, true, false);
normalize(hist, hist, 0, 255, NORM_MINMAX, -1, Mat());

/// Get Backprojection
MatND backproj;
calcBackProject(&hue, 1, 0, hist, backproj, &ranges, 1, true);

/// Draw the backproj
imshow("BackProj", backproj);

/// Draw the histogram
int w = 400; int h = 400;
int bin_w = cvRound((double)w / histSize);
Mat histImg = Mat::zeros(w, h, CV_8UC3);

for (int i = 0; i < bins; i++)
{
rectangle(histImg, Point(i*bin_w, h), Point((i + 1)*bin_w, h - cvRound(hist.at<float>(i)*h / 255.0)), Scalar(0, 255,0), -1);
}

imshow("Histogram", histImg);
}