I have try to get a minRect of a contours(Actually is a triangle). but the result confuse me.!
All of the contours are the same triangle but different rotate angles. but their minRect is different from eachothers. but I think the result should independent of Angle.
brown Rect is 0°
Pink & Green Rect is 45°
other Rect is random。
(I don't have enough reputation to post images,sorry.)
My problem is can I get a minRect which independent of Angle by opencv?
I assume that you mean minAreaRect which by definition finds a rotated rectangle. From the documentation
The function calculates and returns the minimum-area bounding rectangle (possibly rotated) for a specified point set.
Is what you are looking for a function that fits a rectangle that is not rotated?
There is the function boundingRect that does just that
The function calculates and returns the minimal up-right bounding rectangle for the specified point set.
In Python, an example would be to load an image, find the contours and pass the contours to the function.
img =cv2.imread(fileName,0)
#convert the image to B&W with the given threshold. 'thresh' is the
# the B&W image
ret, thresh = cv2.threshold(img,threshold,255,cv2.THRESH_BINARY)
contours, hierarchy = cv2.findContours(thresh, cv2.cv.CV_RETR_LIST,cv2.CHAIN_APPROX_SIMPLE)
cnt = contours[ID] #ID is the index of the contour you want
#find bounding rectangle of countour
x,y,w,h = cv2.boundingRect(cnt)
Actually,I want to get the rotate angle of the countour (a triangle). You can use Excel to draw a triangle(2 sides equal), rotate it. Copy that triangle and rotate it in another angle. Now we got 2 triangle which are the same but different rotate angle. Copy those 2 triangle and copy to MSpaint, save it as image. Use opencv function minAreaRect to find the rotate of the countour(2 triangle).you will find that: if the triangle rotate 0deg or 45deg you will get one type of rect,but if the triangle rotate like 20deg or 60 deg, you will get another type of rect. One type it use the short side to construct the rect, another type it use long side to construct the rect.
#include "stdafx.h"
/**
* @function generalContours_demo2.cpp
* @brief Demo code to obtain ellipses and rotated rectangles that contain detected contours
* @author OpenCV team
*/
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
using namespace cv;
using namespace std;
Mat src; Mat src_gray;
int thresh = 100;
int max_thresh = 255;
RNG rng(12345);
/// Function header
void GetImPath();
void thresh_callback(int, void* );
void ReflashContours();
float trueAngle(Point2f centerP,Point2f midP,float a);
string mypath;
string impath;
/**
* @function main
*/
int main( int argc, char** argv )
{
/// Load source image and convert it to gray
mypath=argv[0];
int pos0=mypath.rfind("\\");
mypath=mypath.substr(0,pos0+1);
if(1==argc)
{
char c='0';
impath=mypath+"t"+ c +".jpg";
}
else
{
impath=argv[1];
}
cout<<impath<<endl;
const char* source_window = "Source";
char k;
while(1){
src = imread (impath, 1 );
/// Convert image to gray and blur it
cvtColor( src, src_gray, COLOR_BGR2GRAY );
blur( src_gray, src_gray, Size(3,3) );
/// Create Window
namedWindow( source_window, WINDOW_AUTOSIZE );
imshow( source_window, src );
createTrackbar( " Threshold:", "Source", &thresh, max_thresh, thresh_callback );
thresh_callback( 0, 0 );
k=waitKey(0);
if (27==k) break;
GetImPath();
cout<<impath<<endl;
}
return(0);
}
void GetImPath()
{
static char c='0';
impath=mypath+"t"+ c +".jpg";
c++;
if( '3'<c) c='0';
return ;
}
void ReflashContours()
{
Mat proc_output;
vector<vector<Point> > contours;
vector<Vec4i> hierarchy;
/// Detect edges using Threshold
//threshold( src_gray, proc_output, thresh, 255, THRESH_BINARY );
// detect edges using canny
Canny(src_gray,proc_output,thresh,thresh*2,3);
//namedWindow( "Proc", WINDOW_AUTOSIZE );
//imshow( "Proc", proc_output );
/// Find contours
findContours( proc_output, contours, hierarchy, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );
cout<< contours.size() <<" Lens found."<<endl;
/// Find the rotated rectangles and ellipses for each contour
vector<RotatedRect> minRect( contours.size() );
vector<RotatedRect> minEllipse( contours.size() );
/// Get the moments
vector<Moments> mu(contours.size() );
for( size_t i = 0; i < contours.size(); i++ )
{ mu[i] = moments( contours[i], false ); }
/// Get the mass centers:
vector<Point2f> mc( contours.size() );
for( size_t i = 0; i < contours.size(); i++ )
{ mc[i] = Point2f( static_cast<float>(mu[i].m10/mu[i].m00) , static_cast<float>(mu[i].m01/mu[i].m00) ); }
for( size_t i = 0; i < contours.size(); i++ )
{
minRect[i] = minAreaRect( Mat(contours[i]) );
minEllipse[i] = fitEllipse( Mat(contours[i]) );
cout<<"Angle: " << trueAngle(mc[i],minRect[i].center, minRect[i].angle)<<"\t [X , Y] = " <<minRect[i].center <<endl;
//cout<<"Angle: " << trueAngle(mc[i],minEllipse[i].center, minEllipse[i].angle)<<"\t [X , Y] = " <<minEllipse[i].center <<endl;
cout<<endl;
}
cout<<endl;
cout<<endl;
/// Draw contours + rotated rects + ellipses
Mat drawing = Mat::zeros( proc_output.size(), CV_8UC3 );
//cout<< "drawing type :"<< drawing.type() <<endl;
drawing=src.clone();
for( size_t i = 0; i< contours.size(); i++ )
{
Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
// contour
drawContours( drawing, contours, (int)i, color, 1, 8, vector<Vec4i>(), 0, Point() );
//drawContours( src, contours, (int)i, color, 1, 8, vector<Vec4i>(), 0, Point() );
/**/
// rotated rectangle
Point2f rect_points[4]; minRect[i].points( rect_points );
for( int j = 0; j < 4; j++ )
{
line( drawing, rect_points[j], rect_points[(j+1)%4], color, 1, 8 );
//line( src, rect_points[j], rect_points[(j+1)%4], color,1 , 8 );
circle(drawing,rect_points[j],j*2,color,-1,8,0);
}
//center point
circle( drawing, mc[i], 1, color, -1, 8, 0 );
circle(drawing,minRect[i].center,1,color,-1,8,0);
//circle(drawing,minEllipse[i].center,1,color,-1,8,0);
//ellipse( drawing, minEllipse[i], color, 1, 8 );
}
/// Show in a window
namedWindow( "Contours", WINDOW_AUTOSIZE );
imshow( "Contours", drawing );
}
/**
* @function thresh_callback
*/
void thresh_callback(int, void* )
{
ReflashContours();
}
float trueAngle(Point2f centerP,Point2f midP,float a)
{
cout<<"centerp: "<<centerP<<"\tmidp: "<<midP<<"\tangle: "<<a<<endl;
//1
if ((midP.x>centerP.x) && (midP.y<centerP.y ))
{
cout<<"1"<<endl;
return -a;
}
//2
else if((midP.x<centerP.x) && (midP.y<centerP.y ))
{
cout<<"2"<<endl;
return 90-a;
}
//3
else if((midP.x<centerP.x) && (midP.y>centerP.y ))
{
cout<<"3"<<endl;
return -180-a;
}
//4
else
{
cout<<"4"<<endl;
return -90-a;
}
}