#include "iostream"
#include "opencv2/opencv.hpp"
using namespace std;
using namespace cv;

int main()
{
	Mat  img, gray;

	img = imread("r4.jpg");
	cvtColor(img, gray, COLOR_BGR2GRAY);

	int nimages = 1;//图片数量
	const int channels[] = { 0 };//需要统计直方图的第几通道
	Mat hist ;//直方图计算的输出值 Mat
	int dims = 1;
	const int histSize[] = { 256 }; //直方图每一个维度划分的柱条的数目
	float pranges[] = { 0, 255 };//取值区间
	const float* ranges[] = { pranges };
	calcHist(&gray, nimages, channels, Mat(), hist, dims, histSize, ranges);

	Mat dst;
	double alpha = 1;
	double beta = 0;
	int norm_type = NORM_INF;
	int  dtype = -1;
	normalize(hist, dst, alpha, beta, NORM_INF, dtype, Mat());

	int hist_height = 256;
	int hist_width = 1024;
	int unit_width = cvRound(hist_width / histSize[0]);
	float rowvalue = 0;
	Point zs, yx, ys;//直方图左上方的点，右上方的点，右下方的点
	Mat picture = Mat::zeros(Size(hist_width, hist_height), CV_8UC3);

	for (int i = 0; i < dst.rows; i++)
	{
		rowvalue = dst.at<float>(i);
		int heighttemp = hist_height - cvRound(hist_height * rowvalue);//翻转
		zs = Point(i*unit_width, heighttemp);
		ys = Point(i*unit_width + 1, heighttemp);
		yx = Point(i*unit_width + 1, hist_height);
		//直方图
		rectangle(picture, zs, yx, Scalar(255, 0, 0));
		//线
		line(picture, zs, ys, Scalar(0, 0, 255));
	}

	imshow("picture", picture);

	waitKey(0);

	return 1;
}