Load, show and convert multiple images - c++

Question

I'm starting to write my first program in C++ with OpenCV and I would like to represent a set of images (stored in my project and libelled "brain_mri_001.jpg -> brain_mri_015.jpg) as vectors of length LxL where L is the number of pixels in the x(y) direction.
Here is my code :
#include "stdafx.h"
#include "cv.h"
#include "highgui.h"
using namespace std;
int main()
{
//load images
for(int i=1; i<=25; i++)
{
char filename[50];
sprintf( filename, "brain_mri_%d.jpg", i );
IplImage *img=cvLoadImage( filename, CV_LOAD_IMAGE_GRAYSCALE);
if (!img)
{
printf("Error: Image not found.\n");
return 2; //error : not found image
}
cvNamedWindow("Projet Image", CV_WINDOW_AUTOSIZE);// create a window
IplImage *img2=cvCloneImage(img); //clone img
cvShowImage("Projet Image", img2); // display the image in a window
cvWaitKey(0); //attendre touche
cvDestroyWindow("Projet Image"); // destroy the window
cvReleaseImage(&img); // memory
return 0; //finish with success
//convert IplImage -> Matrix
int height = img->height;
int width = img->width;
CvMat *mat = cvCreateMat(height,width,CV_32FC3);
//convert Matrix -> Vector
//CvMat row_header, *row;
//row = cvReshape(mat, &row_header, 0, 1);
CvMat vector_header;
cvReshape(img, &vector_header, 0, 1);
//check the height and width of vector_header
if(vector_header.height != 1)
{
fprintf(stderr, "vector_header's height is %d\n", vector_header.height);
}
if(vector_header.width != width*height)
{
fprintf(stderr, "vector_header's width is %d\n", vector_header.width);
}
}
}
I should have made a mistake but I don't know where :(
I would be grateful if anyone can answer me !
P.S. Excuse my bad English...

Answer 1

I think what you need to do is a) cvReleaseImage your images when you're done with them, and 2) your reshape code should be something like this
CvMat vector_header;
cvReshape(img2, &vector_header, 0, 1); /* same # of channels, 1 row */
Note that cvReshape doesn't copy the data, so vector_header doesn't need to be allocated with cvCreateMat. I'm not sure how to test this, except maybe to try loading in a very small image and plotting its values to stdout. As a sanity check, you could check the height and width of vector_header, something like
if(vector_header.height != 1)
{
fprintf(stderr, "vector_header's height is %d\n", vector_header.height);
}
if(vector_header.width != width*height)
{
fprintf(stderr, "vector_header's width is %d\n", vector_header.width);
}
I might have that backwards in terms of height and width. I'm also not 100% sure how the reshape will go, i.e. if your image is [1 2; 3 4], will the resulting vector be [1 2 3 4] or [1 3 2 4]? If you're doing something like PCA (e.g., the eigenfaces algorithm), then it might not matter as long as it's consistent.