To improve the robustness and application area of the algorithm, we further improve the algorithm.

Possible problems we may encounter are:

Shape of target is not rectangle

Dirty marks or obstacles

Incomplete shape of targets

Partly connected with other objects

Focusing on these problems, we improved the algorithm by adding double contour detection, adjusting optimal threshold and so on.

code:

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

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

using namespace cv;
using namespace std;

/**************Definitons*************/
#define MAXRECT				100
#define BUF_SIZE			256
#define CLIENT_ADDRESS		"10.220.12.109"
#define LISTEN_PORT			2000
#define ID					"50-0503334900"
#define THRESH				15
#define AREALIMIT			3000.0
/**************Variables**************/

vector<RotatedRect>		rectProfile;
vector< vector<Point> >	contoursRect;
vector< vector<Point> >	contours;
vector<int> selected;
char buf[BUF_SIZE];
/**************Functions**************/

bool Check(vector<Point> con){
	double area = abs(contourArea(con, 1));
	printf("%lf\n", area);
	if (area < AREALIMIT) 
		return false;
	return true;
}


void ImageProcess(){
	Mat img = imread("total.jpg", CV_LOAD_IMAGE_GRAYSCALE);//sample00012_5.BMP
	Mat imgCanny;
	Canny(img, imgCanny, THRESH, THRESH * 3);
	imshow("imgCanny", imgCanny);
	imwrite("1.ImageCanny.jpg",imgCanny);

	//dilate and erode to connect seperate contour lines
	Mat img_dilate,img_erode;
	dilate ( imgCanny, img_dilate, Mat());
	imshow("Imagedilate", img_dilate);
	imwrite("2.Imagedilate.jpg",img_dilate);
	erode ( img_dilate, img_erode, Mat());
	imshow("Imageerode", img_erode);
	imwrite("3.Imageerode.jpg",img_erode);
	img_dilate.release();
	
	waitKey();

	findContours(img_erode, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_NONE);
	img_erode.release();
	Mat cc = Mat::zeros(imgCanny.rows, imgCanny.cols, CV_8UC3);
	for (int j = 0; j < contours.size(); j++){
		Scalar color(rand()&255, rand()&255, rand()&255);
		drawContours(cc, contours, j, color);
	}
	imshow("ImageContours", cc);
	imwrite("4.ImageContours.jpg",cc);
	cc.release();
	int n = 0;
	contoursRect.clear();
	for (unsigned int i = 0; i < contours.size(); i++){
		//check size
		if (Check(contours[i])){
			contoursRect.push_back(contours[i]);
			n++;
			selected.push_back(i);
		}
	}
	printf("%d\n", n);

	Mat ccc = Mat::zeros(imgCanny.rows, imgCanny.cols, CV_8UC3);
	for (int i = 0; i < n; i++){
		Scalar color(rand()&255, rand()&255, rand()&255);
		drawContours(ccc, contoursRect, i, color,CV_FILLED);
	}
	imshow("ImageRecQualified", ccc);
	imwrite("5.ImageRecSizeQualified.jpg",ccc);
	waitKey();
	

	destroyAllWindows();
	rectProfile.clear();

	//MORPH_OPEN to seperate connected rect
	Mat minrect= Mat::zeros(imgCanny.rows, imgCanny.cols, CV_8UC3);
	Mat element = getStructuringElement(MORPH_ELLIPSE, Size(28,28)); 
	morphologyEx(ccc,minrect,MORPH_OPEN,element);
	imshow("MORPH_OPEN", minrect);
	imwrite("6.ImageMORPH_OPEN.jpg",minrect);
	ccc.release();
	waitKey();

	//find contour again
	Mat minrectgrey=Mat::zeros(imgCanny.rows, imgCanny.cols, CV_8UC1);;
	cvtColor(minrect,minrectgrey,CV_BGR2GRAY);
	Mat imgCanny2= Mat::zeros(imgCanny.rows, imgCanny.cols, CV_8UC1);;
	Canny(minrectgrey, imgCanny2,  1,10);
	imshow("imgCanny2", imgCanny2);
	imwrite("7.ImageCanny2.jpg",imgCanny2);
	
	contours.clear();
	findContours(imgCanny2, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_NONE);

	n = 0;
	contoursRect.clear();
	for (unsigned int i = 0; i < contours.size(); i++){
		if (Check(contours[i])){
			contoursRect.push_back(contours[i]);
			n++;
			selected.push_back(i);
		}
	}
	printf("%d\n", n);

	Mat ccc2 = Mat::zeros(imgCanny.rows, imgCanny.cols, CV_8UC3);
	for (int i = 0; i < n; i++){
		Scalar color(rand()&255, rand()&255, rand()&255);
		drawContours(ccc2, contoursRect, i, color,CV_FILLED);
	}
	imshow("ImageRecQualified2", ccc2);
	imwrite("8.ImageRecQualified2.jpg",ccc2);
	waitKey();

	img = imread("total.jpg");
	Point2f vertices[4];
	for (int i = 0; i < n; i++) {
		rectProfile.push_back(minAreaRect(contoursRect[i]));
		rectProfile[i].points(vertices);
		Scalar color(rand()&255, rand()&255, rand()&255);
		for (int i = 0; i < 4; i++){
			line(img, vertices[i], vertices[(i+1)%4], color,5);
		}
		rectangle(img,Point((vertices[0].x+vertices[2].x)/2-1,(vertices[0].y+vertices[2].y)/2-1),Point((vertices[0].x+vertices[2].x)/2+1,(vertices[0].y+vertices[2].y)/2+1),color,5);
	}
	imshow("ImageRec", img);
	imwrite("9.ImageRec.jpg",img);
	waitKey();
}


int main(){
	contours.reserve(100000*sizeof(Point));
	ImageProcess();
}

This article is among the series of FDUROP project. More information: http://104.131.150.53/thinkcmfx/index.php?g=&m=article&a=index&id=17