Circle and hand detection in OpenCV - c++

Question

Beginner here. I'm trying to detect a circle and hand, and draw a circle around the circle and a rectangle around the hand, and display both in the same image. When I run the program I get some memory error, can anyone please help?
Below is my code:
#include "opencv/cv.h"
#include "opencv2\highgui\highgui.hpp"
#include <iostream>
#include <stdio.h>
#include <math.h>
#include <string.h>
#include <conio.h>
using namespace std;
//declarations
IplImage* img = 0;
CvHaarClassifierCascade *cascade;
CvMemStorage *cstorage;
CvMemStorage *hstorage;
void detectObjects( IplImage *img );
int key;
int main( int argc, char** argv )
{
CvCapture *capture;
IplImage *frame;
// loads classifier for hand haar cascade
char *filename = "haarcascade_hand.xml";
cascade = ( CvHaarClassifierCascade* )cvLoad( "haarcascade_hand.xml", 0, 0, 0 );
// setup memory buffer
hstorage = cvCreateMemStorage( 0 );
cstorage = cvCreateMemStorage( 0 );
// initialize camera
capture = cvCaptureFromCAM( 0 );
// always check
//assert( cascade && storage && capture );
// create a window
cvNamedWindow( "Camera", 1 );
while(key!='q') {
// captures frame and check every frame
frame = cvQueryFrame( capture );
if( !frame ) break;
// detect objects and display video
detectObjects (frame );
// quit if user press 'q'
key = cvWaitKey( 10 );
}
// free memory
cvReleaseCapture( &capture );
cvDestroyAllWindows();
cvReleaseHaarClassifierCascade( &cascade );
cvReleaseMemStorage( &cstorage );
cvReleaseMemStorage( &hstorage );
return 0;
}
void detectObjects( IplImage *img )
{
int px;
int py;
int edge_thresh = 1;
IplImage *gray = cvCreateImage( cvSize(640,480), 8, 1 );
IplImage *edge = cvCreateImage( cvSize(640,480), 8, 1 );
// convert video image color
cvCvtColor(img,gray,CV_BGR2GRAY);
// set the converted image's origin
gray->origin=1;
// color threshold
cvThreshold(gray,gray,100,255,CV_THRESH_BINARY);
// smooths out image
cvSmooth(gray, gray, CV_GAUSSIAN, 11, 11);
// get edges
cvCanny(gray, edge, (float)edge_thresh, (float)edge_thresh*3, 5);
// detects circle
CvSeq* circle = cvHoughCircles(gray, cstorage, CV_HOUGH_GRADIENT, 1, gray->height/50, 5, 35);
// draws circle and its centerpoint
float* p = (float*)cvGetSeqElem( circle, 0 );
cvCircle( img, cvPoint(cvRound(p[0]),cvRound(p[1])), 3, CV_RGB(255,0,0), -1, 8, 0 );
cvCircle( img, cvPoint(cvRound(p[0]),cvRound(p[1])), cvRound(p[2]), CV_RGB(200,0,0), 1, 8, 0 );
px=cvRound(p[0]);
py=cvRound(p[1]);
// displays coordinates of circle's center
cout <<"(x,y) -> ("<<px<<","<<py<<")"<<endl;
// detects hand
CvSeq *hand = cvHaarDetectObjects(img, cascade, hstorage, 1.2, 2, CV_HAAR_DO_CANNY_PRUNING, cvSize(100, 100));
// draws red box around hand when detected
CvRect *r = ( CvRect* )cvGetSeqElem( hand, 0 );
cvRectangle( img,
cvPoint( r->x, r->y ),
cvPoint( r->x + r->width, r->y + r->height ),
CV_RGB( 255, 0, 0 ), 1, 8, 0 );
cvShowImage("Camera",img);
}

Answer 1

The issue is that the size of the gray scale image created should be the same as that of the image obtained from camera.
Instead of:
IplImage *gray = cvCreateImage( cvSize(640,480), 8, 1 );
write it as:
IplImage *gray = cvCreateImage( cvSize(img->width,img->height), 8, 1);

Answer 2

From the error message it seems that you are reading elements of p[] that doesn't exist.
You should check that cvGetSeqElem() actually returns the number of elements you are expecting - it may be that the Hough routines isn't finding any.

Answer 3

I have the same error! You have to add to your code an if statement because when the camera starts cannot "see" any hand so the cvGetSeqElem get no values.
try this instead:
if (hand->total >0) {
CvRect *r = ( CvRect* )cvGetSeqElem( hand, 0 );
cvRectangle(
img,
cvPoint( r->x, r->y ),
cvPoint( r->x + r->width, r->y + r->height ),
CV_RGB( 255, 0, 0 ), 1, 8, 0
);
}