【OpenCV】图像直方图及二维直方图

图像直方图及二维直方图

直方图代码

void QuickDemo::histogram_demo(Mat &image) {
    
    
	// 三通道分离
	std::vector<Mat> bgr_plane;
	split(image, bgr_plane);
	// 定义参数变量
	const int channels[1] = {
    
     0 };
	const int bins[1] = {
    
     256 };
	float hranges[2] = {
    
     0,255 };
	const float* ranges[1] = {
    
     hranges };
	Mat b_hist;
	Mat g_hist;
	Mat r_hist;
	// 计算Blue, Green, Red通道的直方图
	calcHist(&bgr_plane[0], 1, 0, Mat(), b_hist, 1, bins, ranges);
	calcHist(&bgr_plane[1], 1, 0, Mat(), g_hist, 1, bins, ranges);
	calcHist(&bgr_plane[2], 1, 0, Mat(), r_hist, 1, bins, ranges);

	// 显示直方图
	int hist_w = 512;
	int hist_h = 400;
	int bin_w = cvRound((double)hist_w / bins[0]);
	Mat histImage = Mat::zeros(hist_h, hist_w, CV_8UC3);
	// 归一化直方图数据
	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());
	// 绘制直方图曲线
	for (int i = 1; i < bins[0]; 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), 2, 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), 2, 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), 2, 8, 0);
	}
	// 显示直方图
	namedWindow("Histogram Demo", WINDOW_AUTOSIZE);
	imshow("Histogram Demo", histImage);
}

直方图结果展示

二维直方图代码

void QuickDemo::histogram_2d_demo(Mat &image) {
    
    
	// 2D 直方图
	Mat hsv, hs_hist;
	cvtColor(image, hsv, COLOR_BGR2HSV);
	int hbins = 30, sbins = 32;
	int hist_bins[] = {
    
     hbins, sbins };
	float h_range[] = {
    
     0, 180 };
	float s_range[] = {
    
     0, 256 };
	const float* hs_ranges[] = {
    
     h_range, s_range };
	int hs_channels[] = {
    
     0, 1 };
	calcHist(&hsv, 1, hs_channels, Mat(), hs_hist, 2, hist_bins, hs_ranges, true, false);
	double maxVal = 0;
	minMaxLoc(hs_hist, 0, &maxVal, 0, 0);
	int scale = 10;
	Mat hist2d_image = Mat::zeros(sbins*scale, hbins * scale, CV_8UC3);
	for (int h = 0; h < hbins; h++) {
    
    
		for (int s = 0; s < sbins; s++)
		{
    
    
			float binVal = hs_hist.at<float>(h, s);
			int intensity = cvRound(binVal * 255 / maxVal);
			rectangle(hist2d_image, Point(h*scale, s*scale),
				Point((h + 1)*scale - 1, (s + 1)*scale - 1),
				Scalar::all(intensity),
				-1);
		}
	}
	applyColorMap(hist2d_image, hist2d_image, COLORMAP_JET);
	imshow("H-S Histogram", hist2d_image);
	imwrite("D:/hist_2d.png", hist2d_image);
}

二维直方图结果展示