OpenCV学习三十：approxPolyDP 多边拟合函数

Posted 2022-08-16 Thomas会写字

approxPolyDP 主要功能是把一个连续光滑曲线折线化，对图像轮廓点进行多边形拟合。

原理图：对比之前黑点连线，之后蓝色连线：

C++: void approxPolyDP(InputArray curve, OutputArray approxCurve, double epsilon, bool closed)

参数详解;

InputArray curve:一般是由图像的轮廓点组成的点集

OutputArray approxCurve：表示输出的多边形点集

double epsilon：主要表示输出的精度，就是另个轮廓点之间最大距离数，5,6,7，，8，，,,，

bool closed：表示输出的多边形是否封闭

#include <opencv2/opencv.hpp>    
#include <stdio.h>    
#include <stdlib.h>    
#include <iostream>  


using namespace cv;  
using namespace std;  


int main(int argc, char** argv)  
  
	Mat img = imread("4.jpg", -1);
	pyrDown(img, img, Size(img.cols/2, img.rows/2), 4);
	imshow("img", img);imwrite("img.jpg", img);

	//通过canny算法找轮廓，这样 findcontours 的结果会好些
	Mat canny_out;
	Canny(img, canny_out, 45, 127, 3, false);
	imshow("canny_out", canny_out);imwrite("canny_out.jpg", canny_out);

	//寻找轮廓
	vector<vector<Point>> contours;
	vector<Vec4i> hierachy;
	findContours(canny_out, contours, hierachy, RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(-1,-1));
	drawContours(img, contours, -1, Scalar(0,0,255), 1, 8, hierachy);
	
	//定义圆形、方形、旋转矩形、椭圆的存储容器
	vector<vector<Point>> contours_ploy(contours.size());
	vector<Rect> rects_ploy(contours.size());
	vector<Point2f> circle_centers(contours.size());
	vector<float> circle_radius(contours.size());
	vector<RotatedRect> RotatedRect_ploy;//注意：由于下面赋值的过程中有个点数大于5的条件，所以这里没有直接初始化，才有下面pushback的方法添加值。
	vector<RotatedRect> ellipse_ploy;//注意，这里是画椭圆，但是容器类型是 RotatedRect

	//将结果放到各自的容器中
	for (size_t i = 0; i< contours.size(); i++)
	
		approxPolyDP(contours[i], contours_ploy[i], 5, true);
		rects_ploy[i] = boundingRect(contours_ploy[i]);
		minEnclosingCircle(contours_ploy[i], circle_centers[i], circle_radius[i]);

		if (contours_ploy[i].size() >5)
		
			RotatedRect temp1 = minAreaRect(contours_ploy[i]);
			RotatedRect_ploy.push_back(temp1);

			RotatedRect temp2 = fitEllipse(contours_ploy[i]);
			ellipse_ploy.push_back(temp2);
		
	

	//定义最终绘图的图片
	Mat draw_rect(img.size(), img.type(), Scalar::all(0)), 
		draw_rotateRect(img.size(), img.type(), Scalar::all(0)), 
		draw_circle(img.size(), img.type(), Scalar::all(0)), 
		draw_ellipse(img.size(), img.type(), Scalar::all(0));

	//绘图圆形、矩形
	RNG rng(12345);
	for (size_t i = 0; i<contours.size(); i++)
	
		Scalar color = Scalar(rng.uniform(0,255), rng.uniform(0,255), rng.uniform(0,255));
		rectangle(draw_rect, rects_ploy[i], color, 1, 8);
		circle(draw_circle, circle_centers[i], circle_radius[i], color, 1, 8);
	
	imshow("draw_rect", draw_rect);imwrite("draw_rect.jpg", draw_rect);
	imshow("draw_circle", draw_circle);imwrite("draw_circle.jpg", draw_circle);

	//绘图椭圆形、旋转矩形
	Point2f pot[4];
	for (size_t i = 0; i<ellipse_ploy.size(); i++)
	
		Scalar color = Scalar(rng.uniform(0,255), rng.uniform(0,255), rng.uniform(0,255));
		ellipse(draw_ellipse, ellipse_ploy[i], color, 1, 8);

		RotatedRect_ploy[i].points(pot);
		for(int j=0; j<4; j++)
		
			line(draw_rotateRect, pot[j], pot[(j+1)%4], color);
		
	
	imshow("draw_ellipse", draw_ellipse);imwrite("draw_ellipse.jpg", draw_ellipse);
	imshow("draw_rotateRect", draw_rotateRect);imwrite("draw_rotateRect.jpg", draw_rotateRect);


	waitKey();
	return 1;