OpenCV 轮廓过滤 —— Laplacian & Canny 算子与轮廓筛选

#include<opencv2/opencv.hpp>

using namespace cv;

void main() {
	Mat src = imread("F:/VisualStudioSpace/OpenCV/Resource/card.jpg");
	imshow("src", src);
	// 降噪
	Mat gussian;
	GaussianBlur(src, gussian, Size(3, 3), 0);
	// 灰度
	Mat gray;
	cvtColor(gussian, gray, COLOR_BGR2GRAY);
	// 拉普拉斯算法
	Mat dst;
	Mat lpls = (Mat_<char>(3, 3) <<
		0, -1, 0,
		-1, 4, -1,
		0, -1, 0
		);
	filter2D(
		gray,
		dst,
		gray.depth(),
		lpls,
		Point(-1, -1)
	);
	imshow("lpls", dst);
	cvWaitKey(0);
}

#include<opencv2/opencv.hpp>

using namespace cv;

void main() {
	Mat src = imread("F:/VisualStudioSpace/OpenCV/Resource/card.jpg");
	imshow("src", src);
	// 降噪
	Mat gussian;
	GaussianBlur(src, gussian, Size(3, 3), 0);
	// 灰度
	Mat gray;
	cvtColor(gussian, gray, COLOR_BGR2GRAY);
	// 拉普拉斯算法
	Mat lpls;
	Laplacian(
		gray, 
		lpls,   
		CV_16S, // 卷积核的精度
		5       // 卷积核大小
	);
	convertScaleAbs(lpls, lpls);
	imshow("lpls", lpls);
	cvWaitKey(0);
}

#include<opencv2/opencv.hpp>

using namespace cv;

void main() {
	Mat src = imread("F:/VisualStudioSpace/OpenCV/Resource/card.jpg");
	imshow("src", src);
	// canny 算法
	Mat canny;
	// L1gradient: x,y 梯度绝对值求和
	// L2gradient: x,y 求平方根
	Canny(
		src,
		canny,
		50,     // 高低阈值1
		150,    // 高低阈值2, 在 [高低阈值1, 高低阈值2] 之间取 255, 否则取 0
		3,      // 卷积核大小
		false   // 梯度合并类型, L1gradient is false, L2gradient is true
	);
	imshow("canny", canny);
	cvWaitKey(0);
}

#include<opencv2/opencv.hpp>
#include<vector>

using namespace cv;
using namespace std;

void main() {
	Mat src = imread("F:/VisualStudioSpace/OpenCV/Resource/card.jpg");
	imshow("src", src);

	// 1. Canny 边缘检测
	Mat binary;
	Canny(src, binary, 50, 150);
	imshow("binary", binary);

	// 2. 轮廓查询
	vector<vector<Point>> contours;
	findContours(
		binary,
		contours,
		RETR_LIST,
		CHAIN_APPROX_SIMPLE
	);

	// 3. 绘制轮廓
	Mat contour_mat = Mat::zeros(src.size(), CV_8UC3);
	for (int i = 0; i < contours.size(); i++) {
		// 筛选出大于画布一半的轮廓绘制出来
		Rect rect = boundingRect(contours[i]);
		if (rect.width > contour_mat.cols >> 1 && rect.height > contour_mat.rows >> 1) {
			// 绘制轮廓
			drawContours(
				contour_mat,              // 画布
				contours,                 // 轮廓集合
				i,                        // 轮廓索引
				Scalar(0, 255, 0)         // 绘制颜色
			);
			// 绘制矩形框
			rectangle(contour_mat,
				Point(rect.x, rect.y),
				Point(rect.x + rect.width, rect.y + rect.height), 
				Scalar(255, 255, 255)
			);
			break;
		}
	}
	imshow("contour_mat", contour_mat);
	cvWaitKey(0);
	getchar();
}