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OpenCV area selection

I am new to OpenCV and I want to select a specific area in the video / image for detection. In my case, I want to find cars that are only on the road, and not in the parking lot.

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Well, car selection requires the use of training data. But choosing a ROI (area of ​​interest) is quite simple:

Consider img = cv2.imread(image)

In this case, somewhere in your code you can specify an area this way:

sub_image = img[y:y+h, x:x+w]

This will get an ROI if you specify the values, of course, not using "x" or "y", where h is the height and w is the width. Remember that images are only 2D matrices.

CascadeClassifier(), (). . OpenCV , XML.

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(ROI), , , ROI.

, .

.

bool roi_captured = false;
Point pt1, pt2;
Mat cap_img;
//Callback for mousclick event, the x-y coordinate of mouse button-up and button-down 
//are stored in two points pt1, pt2.
void mouse_click(int event, int x, int y, int flags, void *param)
{

    switch(event)
    {
        case CV_EVENT_LBUTTONDOWN:
        {
            std::cout<<"Mouse Pressed"<<std::endl;

            if(!roi_capture)
            {
                pt1.x = x;
                pt1.y = y;
            }
            else
            {
                std::cout<<"ROI Already Acquired"<<std::endl;
            }
        break;
        }
        case CV_EVENT_LBUTTONUP:
        {
          if(!got_roi)
        {
            Mat cl;
            std::cout<<"Mouse LBUTTON Released"<<std::endl;

            pt2.x = x;
            pt2.y = y;
            cl = cap_img.clone();
            Mat roi(cl, Rect(pt1, pt2));
            Mat prev_imgT = roi.clone();
            std::cout<<"PT1"<<pt1.x<<", "<<pt1.y<<std::endl;
            std::cout<<"PT2"<<pt2.x<<","<<pt2.y<<std::endl;

            imshow("Clone",cl);

            got_roi = true;
        }
        else
        {
            std::cout<<"ROI Already Acquired"<<std::endl;
        }
        break;  
        }

    }

}
//In main open video and wait for roi event to complete by the use.
// You capture roi in pt1 and pt2 you can use the same coordinates for processing // //subsequent frame
int main(int argc, char *argv[])
{
    int frame_num = 0;
    int non_decode_frame =0;
    int count = 1, idx =0;
    int frame_pos =0;

    std::cout<<"Video File "<<argv[1]<<std::endl;

    cv::VideoCapture input_video(argv[1]);

    namedWindow("My_Win",1);

    cvSetMouseCallback("My_Win", mouse_click, 0);

    sleep(1);

    while(input_video.grab())
    {
        cap_img.release();

        if(input_video.retrieve(cap_img))
        {
            imshow("My_Win", cap_img);
            if(!got_roi)
            {
                            //Wait here till user select the desire ROI
                waitKey(0);
            }
            else
            {
                std::cout<<"Got ROI disp prev and curr image"<<std::endl;
                std::cout<<"PT1"<<pt1.x<<" "<<pt1.y<<std::endl;
                std::cout<<"PT2"<<pt2.x<<" "<<pt2.y<<std::endl;

                Mat curr_img_t1;
                Mat roi2(cap_img,Rect(pt1, pt2));
                Mat curr_imgT = roi2.clone();
                cvtColor(curr_imgT, curr_img_t1, CV_RGB2GRAY);

                    imshow("curr_img", curr_img);

            // Do remaining processing here on capture roi for every frame
                               waitKey(1);
                        }
                  }
}
}
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