OpenCV How to get width and height of face from image - opencv

Question

Hi I have a large set of images of faces extracted from videos. I would like to simply measure the width and the height of each face found in the images. When I use the HAAR classifiers it returns square faces detected no matter how fat or thin the face was.
There are some improvements that would be ideal, although I'm happy with just the first step.
As a minimum I'm looking for examples to measure the width and height of faces detected in images.
Ideally these faces would first be rotated to facing forwards to measure the width and height of the actual person's face, rather than the pixel width of a potentially rotated face.
Example code would be much appreciated.

Answer 1

Here is the face-detection code. The below two lines will print the width and height of the detected face.
In the first for loop of "detectAndDisplay" add the two lines.
cout << "face width = " << faces[i].width << endl;
cout << "face Height = " << faces[i].height << endl;
Here is the modified code for you:
#include "opencv2/objdetect/objdetect.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
using namespace std;
using namespace cv;
/** Function Headers */
void detectAndDisplay( Mat frame );
/** Global variables */
String face_cascade_name = "haarcascade_frontalface_alt.xml";
CascadeClassifier face_cascade;
string window_name = "Capture - Face detection";
RNG rng(12345);
/** #function main */
int main( int argc, const char** argv )
{
CvCapture* capture;
Mat frame = imread ( "C:\\Desktop\\1.jpg" );
//-- 1. Load the cascades
if( !face_cascade.load( face_cascade_name ) ){ printf("--(!)Error loading\n"); return -1; };
//-- 3. Apply the classifier to the frame
if( !frame.empty() )
{ detectAndDisplay( frame ); }
else
{ printf(" --(!) No captured frame -- Break!"); }
return 0;
}
/** #function detectAndDisplay */
void detectAndDisplay( Mat frame )
{
std::vector<Rect> faces;
Mat frame_gray;
cvtColor( frame, frame_gray, CV_BGR2GRAY );
equalizeHist( frame_gray, frame_gray );
//-- Detect faces
face_cascade.detectMultiScale( frame_gray, faces, 1.1, 2, 0|CV_HAAR_SCALE_IMAGE, Size(30, 30) );
for( int i = 0; i < faces.size(); i++ )
{
cv :: rectangle ( frame, faces[i], Scalar( 255, 0, 255 ), 4 );
cout << "face width = " << faces[i].width << endl;
cout << "face Height = " << faces[i].height << endl;
}
//-- Show what you got
imshow( window_name, frame );
waitKey( 0 );
}