opencv一些基础的代码之直方图绘制

void showHist(Mat& img, Mat& dst)
{
	//1、创建3个矩阵来处理每个通道输入图像通道。
	//我们用向量类型变量来存储每个通道，并用split函数将输入图像划分成3个通道。
	vector<Mat>bgr;
	split(img, bgr);

	//2、定义直方图的区间数
	int numbers = 256;

	//3、定义变量范围并创建3个矩阵来存储每个直方图
	float range[] = { 0,256 };
	const float* histRange = { range };
	Mat b_hist, g_hist, r_hist;

	//4、使用calcHist函数计算直方图
	int numbins = 256;
	calcHist(&bgr[0], 1, 0, Mat(), b_hist, 1, &numbins, &histRange);
	calcHist(&bgr[1], 1, 0, Mat(), g_hist, 1, &numbins, &histRange);
	calcHist(&bgr[2], 1, 0, Mat(), r_hist, 1, &numbins, &histRange);

	//5、创建一个512*300像素大小的彩色图像，用于绘制显示
	int width = 800;
	int height = 600;
	Mat histImage(height, width, CV_8UC3, Scalar(0, 0, 0));

	//6、将最小值与最大值标准化直方图矩阵
	normalize(b_hist, b_hist, 0, height, NORM_MINMAX);
	normalize(g_hist, g_hist, 0, height, NORM_MINMAX);
	normalize(r_hist, r_hist, 0, height, NORM_MINMAX);

	//7、使用彩色通道绘制直方图
	int binStep = cvRound((float)width / (float)numbins);  //通过将宽度除以区间数来计算binStep变量

	for (int i = 1; i < numbins; i++)
	{
		line(histImage,
			Point(binStep * (i - 1), height - cvRound(b_hist.at<float>(i - 1))),
			Point(binStep * (i), height - cvRound(b_hist.at<float>(i))),
			Scalar(255, 0, 0)
		);
		line(histImage,
			Point(binStep * (i - 1), height - cvRound(g_hist.at<float>(i - 1))),
			Point(binStep * (i), height - cvRound(g_hist.at<float>(i))),
			Scalar(0, 255, 0)
		);
		line(histImage,
			Point(binStep * (i - 1), height - cvRound(r_hist.at<float>(i - 1))),
			Point(binStep * (i), height - cvRound(r_hist.at<float>(i))),
			Scalar(0, 0, 255)
		);
	}
	dst = histImage;
	return;
}