Saturday, October 22, 2011

Face Recognition using OpenCV2 and HaarCascade an Intro Part 2

After learning theory a bit in part1 now we lear how we can detect face in an image. Later we will extend this to detecting face from web cam and avi file. The code is very simple. We will load a image of a person in  IplImage structure. We also need to load haarcascader of frontal face will which enable us to detect the face in image. Opencv 2 provides many haar cascades of face, eye , nose etc which ever you want use. If you have installed openCV v2 in "C:/OpenCV2.0" ,you  find it in "C:/OpenCV2.0/data/haarcascades/ Location. Now will need to call "cvHaarDetectObjects" OpenCV Function to detect the faces.

Here is the program -

#include "cv.h"
#include "highgui.h"


#ifdef _EiC
#define WIN32

static CvMemStorage* storage_face = 0; //Memory Storage to Sore faces

static CvHaarClassifierCascade* cascade_face = 0; 

void detect_and_draw( IplImage* image );

//Haar cascade - if your openc CV is installed at location C:/OpenCV2.0/
const char* cascade_name_face ="C:/OpenCV2.0/data/haarcascades/haarcascade_frontalface_alt.xml";


int main()
 IplImage  *image =0;
 image = cvLoadImage("viv6v.jpg",1);
         printf("Error loading image\n");
         return -1;
    cascade_face = (CvHaarClassifierCascade*)cvLoad( cascade_name_face, 0, 0, 0 );
    if( !cascade_face )
        printf("ERROR: Could not load classifier of face  cascade\n" );
        return -1;

    storage_face = cvCreateMemStorage(0);
    cvNamedWindow( "result", 1 );
    // Call function to detect and Draw rectagle around face
    detect_and_draw( image);

    // Wait for key event. 
    // release resourses
    cvReleaseImage( &image );
 cvReleaseHaarClassifierCascade(&cascade_face );
 cvReleaseMemStorage( &storage_face);

    return 0;

////////////////////////////  Function To detect face //////////////////////////

void detect_and_draw( IplImage* img )

    double scale = 2;
    // create a gray image for the input image
    IplImage* gray = cvCreateImage( cvSize(img->width,img->height), 8, 1 );
    // Scale down the ie. make it small. This will increase the detection speed
    IplImage* small_img = cvCreateImage( cvSize( cvRound (img->width/scale),cvRound (img->height/scale)),8, 1 );
    int i;

    cvCvtColor( img, gray, CV_BGR2GRAY );
 cvResize( gray, small_img, CV_INTER_LINEAR );
 // Equalise contrast by eqalizing histogram of image
    cvEqualizeHist( small_img, small_img );
 cvClearMemStorage( storage_face);

    if( cascade_face )
         // Detect object defined in Haar cascade. IN our case it is face
         CvSeq* faces = cvHaarDetectObjects( small_img, cascade_face, storage_face,
                                            1.1, 2, 0/*CV_HAAR_DO_CANNY_PRUNING*/,
                                            cvSize(30, 30) );
        // Draw a rectagle around all detected face 
        for( i = 0; i < (faces ? faces->total : 0); i++ )
            CvRect r = *(CvRect*)cvGetSeqElem( faces, i );
   cvRectangle( img, cvPoint(r.x*scale,r.y*scale),cvPoint((r.x+r.width)*scale,(r.y+r.height)*scale),CV_RGB(255,0,0),3,8,0 );

    cvShowImage( "result", img );
    cvReleaseImage( &gray );
    cvReleaseImage( &small_img );


Output - Image with 1 Face -

Output - Image with multiple Faces -


  1. Can I check with you for OpenCV up to how many faces can detect? Kindly email to lavenderziyi@hotmail.

  2. thank u for the tutorial.
    I am new to MSVC++ and OpenCV, I have this error, from this code, could u guide me how i should fix it?
    my email is,

  3. I missed the error. Here it is,

    1>FaceDetecct.obj : error LNK2019: unresolved external symbol _cvReleaseHaarClassifierCascade referenced in function _main
    1>FaceDetecct.obj : error LNK2019: unresolved external symbol _cvHaarDetectObjects referenced in function "void __cdecl detect_and_draw(struct _IplImage *)" (?detect_and_draw@@YAXPAU_IplImage@@@Z)
    1>c:\users\durat\documents\visual studio 2010\Projects\Facce\Debug\Facce.exe : fatal error LNK1120: 2 unresolved externals

  4. Hello Ritesh Ranjan, your work is nice ,you get some different ideas so please visit online itutorial

  5. thanks for helping me in my project and how can i make my project report and what about report writeing help and Online tutoring, programming help, assignment help, homework help. you can get all on your table from online

  6. Yes, I think there is a large element of wishful thinking.
    English Test Center Pakistan

  7. Nice post.Great blog.Thanks for sharing. It was very interesting and meaningful.Also checkout Surgical instruments Australia

  8. Very informative and well written post! Quite interesting and nice topic chosen for the post.Also checkout Surgical Instrument

  9. Excellent is the only word I can give you for this wonderful blog, keep it up.Also checkout crowd controller