Adding images using opencv - c++

Question

I'm trying to add several images using opencv. I think that my source code should be correct and it compiles without any problems. But when I start the program an error occurs in the for-loop. The problem is that I don't understand why this is happening.
#include <iostream>
#include <sys/types.h>
#include <dirent.h>
#include <errno.h>
#include <vector>
#include <string>
#include <fstream>
#include <cv.h>
#include <highgui.h>
using namespace std;
int get_files(string dir,
vector<string> &files);
int main( int argc, char** argv ){
//---------- Get the names of all *.png files in the directory
string directory = string(".");
vector<string> files = vector<string>();
get_files(directory,files);
//---------- Erase all filenames that aren't *.png files
vector<string> files_format = vector<string>();
for (unsigned int ii = 0; ii < files.size(); ii++) {
files_format.push_back(files[ii]);
string::iterator it;
string format;
files_format[ii].erase(0,files_format[ii].length()-3);
if (files_format[ii] != "png") files.erase(files.begin() + ii);
}
files.erase(files.begin()); // in order to remove the ".." in the beginning
int number_of_files = files.size();
//---------- Create the necessary images
if (files.size() == 0)
return -1;
IplImage* img_firstimage = cvLoadImage(files[0].c_str());
IplImage* img_totalsum = cvCreateImage(cvGetSize(img_firstimage), 8, 1 );
cvCvtColor(img_firstimage, img_totalsum, CV_BGR2GRAY );
//---------- Apply threshold
cvThreshold(img_totalsum, img_totalsum, 150, 1, 1);
//---------- Add all the images
for (unsigned int ii=1; ii < files.size(); ii++){
IplImage* img_load = cvLoadImage(files[ii].c_str());
IplImage* img_add = cvCreateImage(cvGetSize(img_load), 8, 1 );
cvCvtColor(img_load, img_add, CV_BGR2GRAY );
cvThreshold(img_add, img_add, 150, 1, 1);
//----- add the image to the total sum -----
cvAdd(img_totalsum, img_add, img_totalsum);
// ----- release images -----
cvReleaseImage(&img_load);
cvReleaseImage(&img_add);
}
//---------- Invert the total sum image
// -> dense regions are plotted in black
//cvNot(img_totalsum, img_totalsum);
cvNot(img_firstimage, img_firstimage);
//---------- Show the images
cvShowImage("Density Distribution", img_totalsum);
cvShowImage("Negative", img_firstimage);
cvWaitKey(0);
// ----- release images -----
cvReleaseImage(&img_firstimage);
cvReleaseImage(&img_totalsum);
return 0;
}
int get_files(string dir,
vector<string> &files){
DIR *dp;
struct dirent *dirp;
if((dp = opendir(dir.c_str())) == NULL) {
cout << "Error(" << errno << ") opening " << dir << endl;
return errno;
}
while ((dirp = readdir(dp)) != NULL) {
files.push_back(string(dirp->d_name));
}
closedir(dp);
return 0;

Answer 1

It seems, you release your img_add in every loop iteration, but it is created only once. Move the cvReleaseImage(&img_add); instruction outside (directly under) your for loop. That should fix it.
EDIT:
Okay, seems, you fixed that already. Does it work now?
Btw, creating and releasing the img_add inside of your for loop for every newly loaded image is not necessary and is possibly slower, because of the multiple memory allocation and deallocation. You should better allocate it befor entering the loop and release it after the loop.

Answer 2

I solved the problem. I had some other files in the working directory, that weren't *.png files and then the loop didn't work. Absolutely clear that the program couldn't load the other files and work with them... I just don't understand, why the part of the program isn't working that should take care of this problem... Somehow the if (files_format[ii] != "png") files.erase(files.begin() + ii); didn't work properly