Error with working cvConvexityDefect - c

Question

I am right now working with OpenCV and Image processing. and Current topic that i am going through is, Convexity Defect. Following code that is simple program that can illustrates convexity defect, but i am getting error the error which is shown after the code. So please help me
Code :-
#include <cv.h>
#include <highgui.h>
#include <stdio.h>
int g_thresh = 128;
int main(int argc, char **argv)
{
CvMemStorage *hull = cvCreateMemStorage(0);
CvMemStorage *mem = NULL;
CvMemStorage *defe_mem = cvCreateMemStorage(0);
mem = cvCreateMemStorage(0);
CvSeq *contours = NULL;
CvSeq *poly;
CvSeq *convex;
CvSeq *i;
CvSeq *defect;
IplImage *img = cvLoadImage(argv[1], CV_LOAD_IMAGE_COLOR);
IplImage *gray = cvCreateImage(cvGetSize(img), IPL_DEPTH_8U, 1);
cvCvtColor(img, gray, CV_RGB2GRAY);
cvShowImage("Source", img);
cvWaitKey(0);
cvShowImage("DEstination", gray);
cvWaitKey(0);
cvThreshold(gray, gray, g_thresh, 255, CV_THRESH_OTSU);
cvShowImage("BinaryImage", gray);
cvWaitKey(0);
int a = cvFindContours(gray, mem, &contours, sizeof(CvContour), CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE, cvPoint(0, 0));
cvDrawContours(gray, contours, cvScalarAll(255), cvScalarAll(255), 1, 1, 8, cvPoint(0, 0));
cvShowImage("Output",gray);
cvWaitKey(0);
convex = cvConvexHull2(contours, hull, CV_CLOCKWISE, 1);
cvDrawContours(gray, convex, cvScalarAll(255), cvScalarAll(255), 1, 1, 8, cvPoint(0, 0));
cvShowImage("Convex_Hull", gray);
cvWaitKey(0);
//Program Completely Works till here, every thing massed up after this line..
defect = cvConvexityDefects(contours, convex, defe_mem);
for( i = contours; i != 0; i = i->h_next){
cvDrawContours(gray, defect, cvScalarAll(255), cvScalarAll(255), 1, 1, 8, cvPoint(0, 0));
}
//fprintf(stderr, "Convexity Defect::%d\n", cvCheckContourConvexity(contours));
cvShowImage("Convexity", gray );
cvWaitKey(0);
}
Error :-
OpenCV Error: Unsupported format or combination of formats (Convex hull must represented as a sequence of indices or sequence of pointers) in cvConvexityDefects, file /home/akshit/OpenCV/OpenCV-2.4.3/modules/imgproc/src/convhull.cpp, line 544
terminate called after throwing an instance of 'cv::Exception'
what(): /home/akshit/OpenCV/OpenCV-2.4.3/modules/imgproc/src/convhull.cpp:544: error: (-210) Convex hull must represented as a sequence of indices or sequence of pointers in function cvConvexityDefects
Convex hull is found out properly with output, but convexity defect is not found out properly
Any Suggestion?

Answer 1

I think this code snippet should help:
#include <stdlib.h>
#include <stdio.h>
#include <iostream>
#include <ctype.h>
#include <time.h>
#include <opencv2/opencv.hpp>
using namespace cv;
using namespace std;
String window_name = "Hand_HSV";
Mat frame,copyFrame;
// Detect Skin from YCrCb
Mat DetectYCrCb(Mat img,Scalar min, Scalar max)
{
Mat skin;
cvtColor(img, skin, cv::COLOR_RGB2YCrCb);
inRange(skin, min, max, skin);
Mat rect_12 = getStructuringElement(cv::MORPH_RECT, Size(12,12) , Point(6,6));
erode(skin, skin, rect_12,Point(),1);
Mat rect_6 = getStructuringElement(cv::MORPH_RECT, Size(6,6) , Point(3,3));
dilate(skin,skin,rect_6,Point(),2);
return skin;
}
void DetectContour(Mat img)
{
Mat drawing = Mat::zeros( img.size(), CV_8UC3 );
vector<vector<Point> > contours;
vector<vector<Point> > bigContours;
vector<Vec4i> hierarchy;
findContours(img,contours, hierarchy, cv::RETR_LIST, cv::CHAIN_APPROX_SIMPLE, Point());
if(contours.size()>0)
{
vector<vector<int> >hull( contours.size() );
vector<vector<Vec4i>> convDef(contours.size() );
vector<vector<Point>> hull_points(contours.size());
vector<vector<Point>> defect_points(contours.size());
for( int i = 0; i < contours.size(); i++ )
{
if(contourArea(contours[i])>5000)
{
convexHull( contours[i], hull[i], false );
convexityDefects( contours[i],hull[i], convDef[i]);
// start_index, end_index, farthest_pt_index, fixpt_depth
for(int k=0;k<hull[i].size();k++)
{
int ind=hull[i][k];
hull_points[i].push_back(contours[i][ind]);
}
for(int k=0;k<convDef[i].size();k++)
{
if(convDef[i][k][3]>20*256)
{
int ind_0=convDef[i][k][0];
int ind_1=convDef[i][k][1];
int ind_2=convDef[i][k][2];
defect_points[i].push_back(contours[i][ind_2]);
cv::circle(drawing,contours[i][ind_0],5,Scalar(0,255,0),-1);
cv::circle(drawing,contours[i][ind_1],5,Scalar(0,255,0),-1);
cv::circle(drawing,contours[i][ind_2],5,Scalar(0,0,255),-1);
cv::line(drawing,contours[i][ind_2],contours[i][ind_0],Scalar(0,0,255),1);
cv::line(drawing,contours[i][ind_2],contours[i][ind_1],Scalar(0,0,255),1);
}
}
drawContours( drawing, contours, i, Scalar(0,255,0), 1, 8, vector<Vec4i>(), 0, Point() );
drawContours( drawing, hull_points, i, Scalar(255,0,0), 1, 8, vector<Vec4i>(), 0, Point() );
}
}
}
namedWindow( "Hull demo",cv::WINDOW_AUTOSIZE );
imshow( "Hull demo", drawing );
}
int main( int argc, char** argv )
{
VideoCapture capture(0);
//VideoCapture capture("Video_Hand.MPG");
namedWindow( window_name, cv::WINDOW_AUTOSIZE );
if (capture.isOpened()){
while(true)
{
//capture.read(frame);
//flip(frame,frame,1);
capture >> frame;
imshow( window_name, frame);
Mat skinYCrCb = DetectYCrCb(frame,Scalar(0, 100, 80), Scalar(255, 185, 135));
imshow("Result",skinYCrCb);
DetectContour(skinYCrCb);
int c = waitKey(10);
if( (char)c == 27 )
{
break;
}
}
}
return 0;
}