Can someone explain about detectMultiScale in openCV

Question

I've been trying objectDetection in openCV..

Followed a few steps..

Resizing it to 64x64 resolution
Changing it to gray scale
Fetching XML for object detection
Drawing rectangle fringing the pattern

Yet, I couldn't achieve it..

Here's my code :

#include<iostream>
#include "cv.h"
#include "highgui.h"
#include<vector>

using namespace cv;
using namespace std;

int main()
{
    IplImage* img;
    img = cvLoadImage( "hindi3.jpg" );

    vector<cv::Rect> objects;

    // ***Resize image to 64x64 resolution***

    IplImage *resizeImage = cvCreateImage(cvSize(64,64),8,3);

    cvResize(img,resizeImage,CV_INTER_LINEAR);

    cvShowImage("Resize",resizeImage);
    cvWaitKey(0);

    // ***Convert image to grayscale***

    IplImage *grayImage = cvCreateImage(cvGetSize(resizeImage),8,1);

    cvCvtColor(resizeImage,grayImage,CV_BGR2GRAY);

    cvShowImage("gray",grayImage);
    cvWaitKey(0);

    // ***Getting the XML (Cascade xml generated thru haarTraining)***

    CvMemStorage* storage = cvCreateMemStorage(0);
    cout<<"Memory created\n";

    cv::CascadeClassifier cascade;
    cascade.load("cascade.xml");
    //CvHaarClassifierCascade* cascade = (CvHaarClassifierCascade*)cvLoad( "cascade.xml" );
    cout<<"cascade.xml loaded successfully\n";
    double scale = 1.3;

    static CvScalar colors[] = { {{0,0,255}}, {{0,128,255}}, {{0,255,255}},
    {{0,255,0}}, {{255,128,0}}, {{255,255,0}}, {{255,0,0}}, {{255,0,255}} };

    // ***Detect objects***

    cvClearMemStorage( storage );
    objects.clear();
    //CvSeq* objects = cvHaarDetectObjects( grayImage, cascade, storage, 1.1, 4, 0, cvSize( 40, 50 ));
    //cascade.detectMultiScale(grayImage, objects, 1.2, 4, CV_HAAR_DO_CANNY_PRUNING, cvSize(30, 30));
    cascade.detectMultiScale(grayImage, objects, 1.2, 4, CV_HAAR_SCALE_IMAGE, cvSize(30, 30));

    // ***Draw a rectangle outside recognized pattern***

    cout<<"Object size : "<<objects.size();
    for( vector<cv::Rect>::const_iterator r = objects.begin(); r != objects.end(); r++)
    {            //rectangle(img, *r, Scalar(0,0,255), 2, 8, 0);
                 cvRectangle( grayImage, cvPoint( r->x, r->y ), cvPoint( r->x + r->width, r->y + r->height ),Scalar(0,0,255));
                 cout<<"In the loop\n";
    }

    cvNamedWindow( "Output" );
    cvShowImage( "Output", grayImage );
    cvWaitKey(0);

    cvReleaseImage(&resizeImage);
    cvReleaseImage(&grayImage);
    cvReleaseImage( &img );

    return 0;
}

The object size printed by me shows 0 unfortunately :( Hence, it doesn't go to the for loop.. Can anyone help me out..

Thanks in advance

PS : I've commented some lines in the code which were not useful. Please lemme know if I can incorporate the same.

all it means is that you have not detected any objects! you suggested in your code that you might have trained your own haar detector. this could be the issue. or maybe your image just doesn't contain any objects to detect. to debug this i would strongly suggest you use the face detection image that comes with the Opencv samples and use a pre-trained haar face detector. if you get that working i would swap your detector in. if it doesn't work then there is a problem with the detector not your code — morishuz, Apr 29 '13 at 12:42

score 1 · Accepted Answer · edited Nov 23 '13 at 23:12

Found the answer..! I've missed out the specified arguments for detectMultiScale function.

It's working fine..Rectified code as follows

#include<iostream>
#include "cv.h"
#include "highgui.h"
#include<vector>

using namespace cv;
using namespace std;

int main()
{

    IplImage* img;
    img = cvLoadImage( "test.jpg" );

    vector<cv::Rect> objects;

    /*** Resizing is optional***
    *****************************

    IplImage *resizeImage = cvCreateImage(cvSize(64,64),8,3);

    cvResize(img,resizeImage,CV_INTER_LINEAR);
    cvShowImage("Resize",resizeImage);
    cvWaitKey(0);*/

    /*** Change image into grayscale***
    **********************************/

    IplImage *grayImage = cvCreateImage(cvGetSize(img),8,1);
    cvCvtColor(img,grayImage,CV_BGR2GRAY);

    //cvEqualizeHist(grayImage,grayImage); This is optional


    cvShowImage("gray",grayImage);
    cvWaitKey(0);

    CvMemStorage* storage = cvCreateMemStorage(0);
    cout<<"Memory created\n";

    /*** Load the XML generated through haartraining***
    **************************************************/

    cv::CascadeClassifier cascade;
    cascade.load("cascade.xml");
    //CvHaarClassifierCascade* cascade = (CvHaarClassifierCascade*)cvLoad( "cascade.xml" );
    cout<<"cascade.xml loaded successfully\n";
    double scale = 1.3;

    static CvScalar colors[] = { {{0,0,255}}, {{0,128,255}}, {{0,255,255}},
    {{0,255,0}}, {{255,128,0}}, {{255,255,0}}, {{255,0,0}}, {{255,0,255}} };

    /*** Detect objects***
    **********************/

    cvClearMemStorage( storage );
    objects.clear();
    //CvSeq* objects = cvHaarDetectObjects( grayImage, cascade, storage, 1.1, 4, 0, cvSize( 40, 50 ));
    //cascade.detectMultiScale(grayImage, objects, 1.2, 4, CV_HAAR_DO_CANNY_PRUNING, cvSize(30, 30)); if captured through WebCam
    cascade.detectMultiScale(grayImage, objects, 1.1, 3, CV_HAAR_SCALE_IMAGE | CV_HAAR_DO_CANNY_PRUNING,cvSize(0,0), cvSize(100,100));

    cout<<"Object size : "<<objects.size();

    /***Draw Rectangle outside recognized pattern***
    ***********************************************/

    for( vector<cv::Rect>::const_iterator r = objects.begin(); r != objects.end(); r++)
    {            //rectangle(img, *r, Scalar(0,0,255), 2, 8, 0);
                 cvRectangle( grayImage, cvPoint( r->x, r->y ), cvPoint( r->x + r->width, r->y + r->height ),Scalar(0,0,255));
                 cout<<"In the loop\n";
    }

    cvNamedWindow( "Output" );
    cvShowImage( "Output", grayImage );
    cvWaitKey(0);

    //cvReleaseImage(&resizeImage); If resized
    cvReleaseImage(&grayImage);
    cvReleaseImage( &img );

    return 0;
}

And finally this worked..!

PS: This program holds good only when the input is taken through image unlike WebCam or Video.

Can someone explain about detectMultiScale in openCV

1 Answers1

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