OpenCv assertion failed - c++

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!

Answer 1

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