Drawing Bounding-Box using OpenCV in C++ Enviroment - c++

Question

Hello peeps I have developed a piece of software that draws contours of the input image, now I wont to take this to the next level and draw Bounding Box around objects of interest i.e. A person. I looked at boundingRect() function but i am struggling to understand it. Maybe there are different functions algorithms draw Bounding Box.....?
Here is the code of my program:
#include "iostream"
#include<opencv\cv.h>
#include<opencv\highgui.h>
#include<opencv\ml.h>
#include<opencv\cxcore.h>
#include <iostream>
#include <string>
#include <opencv2/core/core.hpp> // Basic OpenCV structures (cv::Mat)
#include <opencv2/highgui/highgui.hpp> // Video write
using namespace cv;
using namespace std;
Mat image; Mat image_gray; Mat image_gray2; Mat threshold_output;
int thresh=100, max_thresh=255;
int main(int argc, char** argv) {
//Load Image
image =imread("C:/Users/Tomazi/Pictures/Opencv/tomazi.bmp");
//Convert Image to gray & blur it
cvtColor( image,
image_gray,
CV_BGR2GRAY );
blur( image_gray,
image_gray2,
Size(3,3) );
//Threshold Gray&Blur Image
threshold(image_gray2,
threshold_output,
thresh,
max_thresh,
THRESH_BINARY);
//2D Container
vector<vector<Point>> contours;
//Fnd Countours Points, (Imput Image, Storage, Mode1, Mode2, Offset??)
findContours(threshold_output,
contours, // a vector of contours
CV_RETR_EXTERNAL,// retrieve the external contours
CV_CHAIN_APPROX_NONE,
Point(0, 0)); // all pixels of each contours
// Draw black contours on a white image
Mat result(threshold_output.size(),CV_8U,Scalar(255));
drawContours(result,contours,
-1, // draw all contours
Scalar(0), // in black
2); // with a thickness of 2
//Create Window
char* DisplayWindow = "Source";
namedWindow(DisplayWindow, CV_WINDOW_AUTOSIZE);
imshow(DisplayWindow, result);
waitKey(5000);
return 1;
}
Can anyone suggest an solution...? Perhaps direct me to some sources, tutorials etc. Reading OpenCV documentation and looking at the boundingRect() function i still dont understand. HELP PLEASE :)

Answer 1

But you can also easily compute the bounding box yourself and then draw them using the rectangle function:
int maxX = 0, minX = image.cols, maxY=0, minY = image.rows;
for(int i=0; i<contours.size(); i++)
for(int j=0; j<contours[i].size(); j++)
{
Point p = contours[i][j];
maxX = max(maxX, p.x);
minX = min(minX, p.x);
maxY = max(maxY, p.y);
minY = min(minY, p.y);
}
rectangle( result, Point(minX,minY), Point(maxX, maxY), Scalar(0) );

Answer 2

This link was not helpful?
I think it demonstrates how to take the contour object and make it a polygon approximation, plus how to draw the bounding rectangle around it.
It seems to be one of the basic OpenCV demos.

Answer 3

I've talked about the bounding box technique in these posts:
How to detect Text Area from image?
Contours opencv : How to eliminate small contours in a binary image
OpenCv 2.3 C - How to isolate object inside image (simple C++ demo)
I think that the last one can probably help you understand how the standard technique works. What OpenCV offers is an easier approach.