Table of contents
1. The maximum rectangle bounding the outline boundingRect()
2. Minimum rectangle surrounding the outline minAreaRect()
3. Contour external polygon approxPolyDP()
1. The maximum rectangle bounding the outline boundingRect()
Rect cv::boundingRect ( InputArray array )
- array: input grayscale image or 2D point set, data type is vector<Point> or Mat.
Sample code:
//轮廓最大外接矩阵
void Contour_external_maxmatrix(Mat image) {
Mat gray,binary;
cvtColor(image,gray,COLOR_BGR2GRAY);//灰度化
GaussianBlur(gray,gray,Size(9,9),2,2);//滤波
threshold(gray,binary,170,255,THRESH_BINARY|THRESH_OTSU);//自适应二值化
//轮廓检测
vector<vector<Point>> contours;//轮廓
vector<Vec4i> hierarchy;//存放轮廓结构变量
findContours(binary,contours,hierarchy,RETR_TREE,CHAIN_APPROX_SIMPLE,Point());
//寻找轮廓的外接矩阵
for(int n=0;n<contours.size();n++) {
//最大外接矩阵
Rect rect = boundingRect(contours[n]);
rectangle(image, rect, Scalar(7, 67, 255), 2, 8, 0);
}
imwrite("/sdcard/DCIM/max.png",image);
}The result of contour circumscribing the largest rectangle:
2. Minimum rectangle surrounding the outline minAreaRect()
RotatedRect cv::minAreaRect ( InputArray points )
- array: input grayscale image or 2D point set, data type is vector<Point> or Mat.
Sample code:
//轮廓最小外接矩阵
void Contour_external_minmatrix(Mat image){
Mat gray,binary;
cvtColor(image,gray,COLOR_BGR2GRAY);//灰度化
GaussianBlur(gray,gray,Size(9,9),2,2);//滤波
threshold(gray,binary,170,255,THRESH_BINARY|THRESH_OTSU);//自适应二值化
//轮廓检测
vector<vector<Point>> contours;//轮廓
vector<Vec4i> hierarchy;//存放轮廓结构变量
findContours(binary,contours,hierarchy,RETR_TREE,CHAIN_APPROX_SIMPLE,Point());
//寻找轮廓的外接矩阵
for(int n=0;n<contours.size();n++) {
//最小外接矩阵
RotatedRect rrect= minAreaRect(contours[n]);
Point2f points[4];
rrect.points(points);//读取最小外接矩阵的四个顶点
Point2f cpt=rrect.center;//最小外接矩阵的中心
//绘制旋转矩阵与中心位置
for(int i=0;i<4;i++){
if(i==3){
line(image,points[i],points[0],Scalar(0,0,255,255),2,8,0);
break;
}
line(image,points[i],points[i+1],Scalar(0,0,255,255),2,8,0);
}
//绘制矩阵中心
circle(image,cpt,4,Scalar(0,0,255,255),-1,8,0);
}
imwrite("/sdcard/DCIM/min.png",image);
}
The result of contour circumscribing the smallest rectangle:
3. Contour external polygon approxPolyDP()
void cv::approxPolyDP (InputArray curve,
OutputArray approxCurve,
double epsilon,
bool closed
）
- curve: input contour pixels.
- approxCurve: polygon approximation result, given in the form of polygon vertex coordinates
- epsilon: The accuracy of the approximation, that is, the maximum distance between the original curve and the approximated curve.
- closed: A sign of whether the approaching curve is a closed curve. true means the curve is closed, that is, the last vertex is connected to the first vertex.
Sample code:
void drawapp(Mat result,Mat img2){
for(int i=0;i<result.rows;i++){
//最后一个坐标点与第一个坐标点连接
if(i==result.rows-1){
Vec2i point1=result.at<Vec2i>(i);
Vec2i point2=result.at<Vec2i>(0);
line(img2,point1,point2,Scalar(0,0,255,255),4,8,0);
break;
}
Vec2i point1=result.at<Vec2i>(i);
Vec2i point2=result.at<Vec2i>(i+1);
line(img2,point1,point2,Scalar(0,0,255,255),4,8,0);
}
}
//轮廓多边形拟合
void Contour_external_matrix(Mat image){
Mat gray,binary;
cvtColor(image,gray,COLOR_BGR2GRAY);//灰度化
// GaussianBlur(gray,gray,Size(9,9),2,2);//滤波
// threshold(gray,binary,170,255,THRESH_BINARY|THRESH_OTSU);//自适应二值化
//轮廓的发现与绘制
vector<vector<Point>> contours;//轮廓
vector<Vec4i> hierarchy;//存放轮廓结构变量
findContours(gray,contours,hierarchy,RETR_TREE,CHAIN_APPROX_SIMPLE,Point());
//绘制多边形
for(int n=0;n<contours.size();n++) {
//用最小外接矩阵求取轮廓中心
RotatedRect rrect= minAreaRect(contours[n]);
Point2f center=rrect.center;//最小外接矩阵的中心
circle(image,center,2,Scalar(0,0,255,255),2,8,0);
Mat result;
approxPolyDP(contours[n],result,4,true);//多边形拟合
drawapp(result,image);
}
imwrite("/sdcard/DCIM/matrix.png",image);
}The result of polygon fitting:
