Segmentation fault while tring to use openCV - c++

Question

I keep getting segmentation fault while trying to run this code. I tried running it by changing the data types. Is it a problem with data types such that uchar and float number of bytes do not match. If so what to do?
#include "opencv2/highgui/highgui.hpp"
#include <iostream>
using namespace cv;
using namespace std;
int main( int argc, const char** argv )
{
Mat img = imread("/home/sahiti/Downloads/images3.png", CV_LOAD_IMAGE_UNCHANGED); //read the image data in the file "MyPic.JPG" and store it in 'img'
if (img.empty()) //check whether the image is loaded or not
{
cout << "Error : Image cannot be loaded..!!" << endl;
//system("pause"); //wait for a key press
return -1;
}
Mat image;
img.convertTo(image,CV_32F);
int w,h;
for(w=0;w<img.size().width;w++)
{
for(h=0;h<img.size().height;h++)
{
Vec3f intensity = img.at<Vec3f>(w, h);
float blue = intensity.val[0];
float green = intensity.val[1];
float red = intensity.val[2];
float lumin=(0.2126 * red + 0.7152 *green + 0.0722 *blue);
image.at<float>(w,h)=lumin;
}
}
Mat im;
image.convertTo(im,CV_8UC1);
imwrite( "/home/sahiti/gray_Image.png", im );
return 0;
}

Answer 1

This line
Vec3f intensity = img.at<Vec3f>(w, h);
should be
Vec3f intensity = image.at<Vec3f>(w, h);
Also this does not make sense:
image.at<float>(w,h)=lumin;
That is trying to write a single result into a three channel image.
This might make more sense:
#include "opencv2/highgui/highgui.hpp"
#include <iostream>
using namespace cv;
using namespace std;
int main( int argc, const char** argv )
{
Mat img = imread("/home/sahiti/Downloads/images3.png", CV_LOAD_IMAGE_UNCHANGED); //read the image data in the file "MyPic.JPG" and store it in 'img'
if (img.empty()) //check whether the image is loaded or not
{
cout << "Error : Image cannot be loaded..!!" << endl;
//system("pause"); //wait for a key press
return -1;
}
Mat image;
Mat im(img.size(), CV_8UC1);
img.convertTo(image,CV_32F);
int w,h;
for(w=0;w<img.size().width;w++)
{
for(h=0;h<img.size().height;h++)
{
//Vec3f intensity = img.at<Vec3f>(w, h);
Vec3f intensity = image.at<Vec3f>(w, h);
float blue = intensity.val[0];
float green = intensity.val[1];
float red = intensity.val[2];
float lumin=(0.2126 * red + 0.7152 *green + 0.0722 *blue);
//image.at<float>(w,h)=lumin;
im.at<uint8>(w,h)=lumin;
}
}
//Mat im;
//image.convertTo(im,CV_8UC1);
imwrite( "/home/sahiti/gray_Image.png", im );
return 0;
}