OpenCv assertion failed

Question

I am working on application for finding face in 2D image and later inside same image I want to find mouth, but I have some problem right now. This is my code so far:

for (int i = 0; i < faces.size(); i++)
{
        Point pt1(faces[i].x, faces[i].y);
        Point pt2((faces[i].x + faces[i].height), (faces[i].y + faces[i].width));
        rectangle(frame, pt1, pt2, Scalar(255,0 , 0), 2, 8, 0);

                    //I WANT ROI(FOR MOUTH DETECTION) TO BE ONLY HALF OF THE RECTANGLE WITH FACE
        Rect mouthROI;
        mouthROI.x = (faces[i].x);
        mouthROI.y = faces[i].y*(1.5);
        mouthROI.width = (faces[i].x + faces[i].height);
        mouthROI.height = (faces[i].y + faces[i].width);

                    //I CHECK IF NEW RECTANGLE IS EXACTLY BOTTOM HALF OF PREVIOUS ONE
        Point ptAA(mouthROI.x, mouthROI.y);
        Point ptBB(mouthROI.width, mouthROI.height);
        rectangle(frame, ptBB, ptAA, Scalar(0,0 , 255), 2, 2, 0);


        Mat image_roi = frame(mouthROI);

        cvtColor(frame, frame_gray, COLOR_BGR2GRAY);
        equalizeHist( frame_gray, frame_gray );

                    // DETECTING MOUTH INSIDE ROI OF EARLIER DETECTED FACE
        mouth_cascade.detectMultiScale(image_roi, mouths, 1.1, 2, 0, Size(30, 30));

        for(int i = 0; i < mouths.size(); i++)
        {
            Point pt1(mouths[i].x, mouths[i].y); // Display detected faces on main window - live stream from camera
            Point pt2((mouths[i].x + mouths[i].height), (mouths[i].y + mouths[i].width));
            rectangle(frame, pt1, pt2, Scalar(0, 255, 0), 2, 8, 0);
        }

}

Unfortunately this code does not work. I get error like this:

OpenCV Error: Assertion failed (0 <= roi.x && 0 <= roi.width && roi.x + roi.width <= m.cols && 0 <= roi.y && 0 <= roi.height && roi.y + roi.height <= m.rows) in cv::Mat::Mat(const cv::Mat&, const cv::Rect&), file C:/build/2_4_PackSlave-win32-vc11-shared/opencv/modules/core/src/matrix.cpp, line 323

How can I fix this error. Thank You all for help!

The parameters you pass to the function throwing the assert are incorrect. Use a debugger to figure out which function is throwing the assert and back trace it to the line in your code that initiates the call. — Captain Obvlious, Jan 21 '14 at 03:46
Error is in this place `Mat image_roi = frame(mouthROI);` , but I still don't know why... — Michal_LFC, Jan 21 '14 at 03:49
Check out [Similar link](http://stackoverflow.com/questions/20855192/assertion-error-in-grabcut) and see if you did not commit same error. — BlueSword, Jan 21 '14 at 05:21

score 5 · Accepted Answer · edited Jun 23 '15 at 13:02

The way you have initialized mouthROI is incorrect. It should be like this instead,

<previous code>
mouthROI.width = (faces[i].height);
mouthROI.height = (faces[i].width);

Point ptAA(mouthROI.x, mouthROI.y);
Point ptBB(mouthROI.x+mouthROI.width, mouthROI.y+mouthROI.height);

Remember that cv::Rect doesn't take the position of the rectangle, it takes the position of the upper left corner and the width and the height.. Refer to the documentation for further details.

HTH

OpenCv assertion failed

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