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@Guanta Can you please help me how to go about the step 4 if my aim is just to find similar images and not to train? How to go about it once I have completed steps 1-3 and have the descriptors. Please help

 std::vector<std::vector<cv::Point> > contours;

std::vector<cv::Vec4i> hierarchy;

cv::findContours(ThreshIm,contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_NONE);

cv::fillPoly(ThreshIm,contours,Scalar(255)); cv::drawContours(frame,contours,-1,Scalar(0,255,0),3);

// cv::RotatedRect box= cv::minAreaRect(Mat(contours[0]));

While taking a live input from camera, the program runs successfully until the cv::RotatatedRect is not included in the code,but as soon as the program is run with this line, the program crashes. What might be happening?

std::vector<cv::point> points;

      cv::Mat_<uchar>::iterator it = ThreshIm.begin<uchar>();
      cv::Mat_<uchar>::iterator end = ThreshIm.end<uchar>();
      for (; it != end; ++it)
        if (*it)
          points.push_back(it.pos());

        cv::RotatedRect box;

           box = cv::minAreaRect(Mat(points));

The program builds successfully but then upon running(on qt-creator IDE)the following error is shown:

what(): /build/buildd/opencv-2.3.1/modules/imgproc/src/utils.cpp:53: error: (-5) Input array is not a valid matrix in function cvPointSeqFromMat

The program has unexpectedly finished.

What might be going wrong?

I'm using the following code (in qtcreator IDE) for taking live input video from webcam

void MainWindow::on_pushButton_clicked() {

cv::VideoCapture cap(0); cv::Mat frame; ui->horizontalSlider->setRange(0,255); while(true){

cap >> frame;

cv::cvtColor(frame,frame,CV_BGR2GRAY);
cv::cvtColor(frame,frame,CV_GRAY2RGB);
QImage img= QImage((const unsigned char*)(frame.data),
frame.cols,frame.rows,QImage::Format_RGB888);

ui->label->setPixmap(QPixmap::fromImage(img));

ui->label->resize(ui->label->pixmap()->size());

int j= ui->horizontalSlider->value(); ui->label_2->setNum(j);

double l=0; l++; std::cout<<l; ui-="">label_3->setNum(l); cv::waitKey(30);

} } The problem is that value of l is not updating,i.e. it updates to 1 once and then stops updating, how is the while loop running then?