opencv学习笔记十八：直方图计算

直方图统计，分别统计不同灰度值的个数，并画出其直方图。

API函数：calcHist(&image, 1, 0, Mat(), result, dims, &histSize, &ranges);

参数解释：单通道图像地址，计算多少张通常取1，通道数通常取0，掩模通常取Mat() , 统计的结果，维数，分了多少个灰度等级，灰度范围。

#include
using namespace cv;
using namespace std;
int main(int arc, char** argv)
{   
	Mat src, dst,b,g,r;
	src = imread("2.jpg");
	namedWindow("input",CV_WINDOW_AUTOSIZE);
	imshow("input", src);

	vector channels;
	split(src, channels);
	b = channels[0];
	g = channels[1];
	r = channels[2];
	Mat b_hist, g_hist, r_hist;
	int histSize = 256; 
	float range[] = { 0, 256 }; 
	const float* ranges = { range };

	calcHist(&b, 1, 0, Mat(), b_hist, 1, &histSize, &ranges);
	calcHist(&g, 1, 0, Mat(), g_hist, 1, &histSize, &ranges);
	calcHist(&r, 1, 0, Mat(), r_hist, 1, &histSize, &ranges);

	int hist_w = 512; int hist_h = 400;
	int bin_w = hist_w / histSize;

	Mat histImage(hi