Wrong cv::face FacemarkLBF instantiation - c++

Question

I am using OpenCV 4.4.0 on Ubuntu 20.04 with the installed latest opencv_contrib extra modules. For detecting the face landmarks (based on this tutorial) I use the following #include and namespace sections related to the extra face module :
#include <opencv2/face.hpp>
using namespace cv::face;
The face.hpp file is detected (therefore I assume correct installation of the opencv_contrib modules), but e.g. the line
Ptr<facemark> facemark = FacemarkLBF::create();
throws an error
error: ‘facemark’ was not declared in this scope
I have already tried installing the extra modules with both cmake-gui and with the cmake terminal command. The results are the same. I assume there is an error related to the namespace cv::face. Any ideas on what kind of mistake I am doing here?
The minimal code is here:
#include <opencv2/opencv.hpp>
#include <opencv2/face.hpp>
#include "drawLandmarks.hpp"
using namespace std;
using namespace cv;
using namespace cv::face;
int main(int argc,char** argv)
{
// Load Face Detector
CascadeClassifier faceDetector("haarcascade_frontalface_alt2.xml");
// Create an instance of Facemark
Ptr<facemark> facemark = FacemarkLBF::create();
// Load landmark detector
facemark->loadModel("lbfmodel.yaml");
// Set up webcam for video capture
VideoCapture cam(0);
// Variable to store a video frame and its grayscale
Mat frame, gray;
// Read a frame
while(cam.read(frame))
{
// Find face
vector<rect> faces;
// Convert frame to grayscale because
// faceDetector requires grayscale image.
cvtColor(frame, gray, COLOR_BGR2GRAY);
// Detect faces
faceDetector.detectMultiScale(gray, faces);
// Variable for landmarks.
// Landmarks for one face is a vector of points
// There can be more than one face in the image. Hence, we
// use a vector of vector of points.
vector< vector<point2f> > landmarks;
// Run landmark detector
bool success = facemark->fit(frame,faces,landmarks);
if(success)
{
// If successful, render the landmarks on the face
for(int i = 0; i < landmarks.size(); i++)
{
drawLandmarks(frame, landmarks[i]);
}
}
// Display results
imshow("Facial Landmark Detection", frame);
// Exit loop if ESC is pressed
if (waitKey(1) == 27) break;
}
return 0;
}

Answer 1

As #john and #idclev 463035818 have suggested, the way for creating an instance of Facemark is
Ptr<FacemarkLBF> facemark = FacemarkLBF::create();
e.g. if I want to call it facemark.