ROI/ Bounding Box selection of Mat images in OpenCV [closed]

asked 2016-06-22 06:40:04 -0500

patri gravatar image

I'm trying to write a program that opens my laptops camera and gets a video stream and writes it to a video file on my computer. You should be able to pause and unpause the video, the pause option is added because I want to select an object within the video and the location of the object might differ. The issue I am facing is, that every time I run the program on Visual C++(with OpenCV 3.1), when I first press the r button(for pause), even though the video appears to be paused, if the location of the object changes(from the moment I press pause till the moment I've selected the ROI), in the new window that contains the ROI I'll have what it is in that moment in that area, even though the object has moved, so the video is not actually paused, only the writing to the video file stops. Another problem I am facing, is that after selecting the ROI, I cant pause/unpause the writing to the video file(it works just fine when I'm not selecting the ROI). I really need a still image because I have to use it in further processing.

Please help me find the problem.

#include <iostream>     // std::cout, std::endl
#include <iomanip>      // std::setfill, std::setw
#include <opencv\cv.h>
#include <opencv2/highgui/highgui.hpp>
#include <time.h>
#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>

using namespace std;
using namespace cv;

Point point1, point2; /* vertical points of the bounding box */
int drag = 0;
Rect rect; /* bounding box */
Mat img, roiImg; /* roiImg - the part of the image in the bounding box */
int select_flag = 0;

void mouseHandler(int event, int x, int y, int flags, void* param)
if (event == CV_EVENT_LBUTTONDOWN && !drag)
/* left button clicked. ROI selection begins */
point1 = Point(x, y);
drag = 1;

if (event == CV_EVENT_MOUSEMOVE && drag)
/* mouse dragged. ROI being selected */
Mat img1 = img.clone();
point2 = Point(x, y);
rectangle(img1, point1, point2, CV_RGB(255, 0, 0), 3, 8, 0);
imshow("PausedVideo", img1);

if (event == CV_EVENT_LBUTTONUP && drag)
point2 = Point(x, y);
rect = Rect(point1.x, point1.y, x - point1.x, y - point1.y);
drag = 0;
roiImg = img(rect);

if (event == CV_EVENT_LBUTTONUP)
/* ROI selected */
select_flag = 1;
drag = 0;

string intToString(int number) {

std::stringstream ss;
ss << number;
return ss.str();

int main(int argc, char* argv[])
bool recording = false;
bool startNewRecording = false;
int inc = 0;
bool firstRun = true;

VideoCapture cap(0); // open the video camera no. 0
VideoWriter oVideoWriter;//create videoWriter object, not initialized yet

if (!cap.isOpened())  // if not success, exit program
cout << "ERROR: Cannot open the video file" << endl;
return -1;

namedWindow("MyVideo", CV_WINDOW_AUTOSIZE); //create a window called "MyVideo"

double dWidth = cap.get(CV_CAP_PROP_FRAME_WIDTH); //get the width of frames of the video
double dHeight = cap.get(CV_CAP_PROP_FRAME_HEIGHT); //get the height of frames of the video

cout << "Frame Size = " << dWidth << "x" << dHeight << endl;

//set framesize for use with videoWriter
Size frameSize(static_cast<int>(dWidth), static_cast<int ...
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Closed for the following reason the question is answered, right answer was accepted by sturkmen
close date 2020-10-08 07:03:51.992913


try to use CV_FOURCC('M', 'J', 'P', 'G') instead of CV_FOURCC('D', 'I', 'V', '3')

LBerger gravatar imageLBerger ( 2016-06-22 15:26:32 -0500 )edit