OpenCV: Eigenfaces with CSV file - c++

Question

I'm struggling with this issue for quite some time now and maybe someone here might have a suggestion of what's going wrong. I'm trying to use the libfacerec to implement Eigenfaces in OpenCV from this site: https://github.com/bytefish/libfacerec I'm using OpenCV-2.3.1 with Visual Studio 2010
The sample code usess the orl_faces dataset from this site: http://www.cl.cam.ac.uk/research/dtg/attarchive/facedatabase.html and loads these images by using a csv file. In this file all paths to all 400 images (10 images of 40 different people) are listed and a label is attached to each persons. Both entries are seperated by a " ; ". I've added a few lines of this csv file below:
C:/Users/PIMMES/Documents/libraries/orl_faces/s1/1.pgm;0
C:/Users/PIMMES/Documents/libraries/orl_faces/s1/2.pgm;0
...
C:/Users/PIMMES/Documents/libraries/orl_faces/s2/1.pgm;1
C:/Users/PIMMES/Documents/libraries/orl_faces/s2/2.pgm;1
...
etc
I've added the piece of code below which should load the image data. This is exactly the same piece of code as listed in the main.cpp file in the /src folder from the libfacerec website:
void read_csv(const string& filename, vector<Mat>& images, vector<int>& labels, char separator = ';')
{
std::ifstream file(filename.c_str(), ifstream::in);
if (!file) throw std::exception();
string line, path, classlabel;
while (getline(file, line))
{
stringstream liness(line);
getline(liness, path, separator);
getline(liness, classlabel);
images.push_back(imread(path, 0));
labels.push_back(atoi(classlabel.c_str()));
}
}
int main(int argc, const char *argv[])
{
// check for command line arguments
if(argc != 2)
{
cout << "usage: " << argv[0] << " <csv.ext>" << endl;
exit(1);
}
// path to your CSV
string fn_csv = string(argv[1]);
// images and corresponding labels
vector<Mat> images;
vector<int> labels;
// read in the data
try
{
read_csv(fn_csv, images, labels);
}
catch (exception& e)
{
cerr << "Error opening file \"" << fn_csv << "\"." << endl;
exit(1);
}
// get width and height
int width = images[0].cols;
int height = images[0].rows;
// get test instances
Mat testSample = images[images.size() - 1];
int testLabel = labels[labels.size() - 1];
...
etc.
}
The whole project builds fine without any errors, but when I try to run a crash occurs. I went into Debug mode and figured that both vector< Mat > images and vector< int > labels (don't mind the spaces cause without them it doesn't display properly here) are still 0 which means no data is loaded. However when I print the variables height and width it show 140 for both (all images from orl_faces are 140x140 pixels)
So my question, what is going wrong? Why aren't both vectors filled while height and width are filled?
Edit: It seems that both vectors are filled correctly on my other pc (vector images [400], vector labels [400]. However the program still crashes and when running Debug I find this error:
Unhandled exception at 0x77c415de in Test.exe: 0xC0000005: Access violation writing location 0x00000000.
It is located in the mat.hpp file and when stepping through this file, a vector v shows these errors:
[size] CXX0030: Error: expression cannot be evaluated
[capacity CXX0030: Error: expression cannot be evaluated

Answer 1

I am pretty sure the problem is this.
You are linking against the libraries:
opencv_core231.lib
opencv_highgui231.lib
opencv_imgproc231.lib
And then you build with the Debug Configuration in Visual Studio. See the problem? If you want to do this switch to the opencv_core231d.lib libraries. BUT: The OpenCV2.3.1 superpack for some mysterious reasons doesn't come with the tbb_debug.dll, so the Debug build is going to fail. If you are using the superpack and want to use libfacerec, then activate the Release Build Configuration in Visual Studio, build & run and everything is going to work just fine.
I've written a tutorial on it, which should be easy to follow: http://www.bytefish.de/blog/opencv_visual_studio_and_libfacerec. Scroll to the very bottom to see the Eigenfaces in Windows. So you see, it actually works.