xcode - Open CV, image loading issue on Mac OS X

Question

I think my question is pretty basic. I was trying to get Open CV to install on my OSX Lion. I had followed all the steps recommended on this link http://tilomitra.com/opencv-on-mac-osx/

However, when I run the C++ code recommended on the website in Xcode, it fails to load an image with the cvLoadImage( ) function. I have placed my image in the project folder (as recommended). Here is the code I was running:

// Example showing how to read and write images
#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv/cvaux.hpp>

int main(int argc, char** argv)
{
IplImage * pInpImg = 0;

// Load an image from file - change this based on your image name
pInpImg = cvLoadImage("my_image.jpg", CV_LOAD_IMAGE_UNCHANGED);
if(!pInpImg)
{
 fprintf(stderr, "failed to load input image
");
 return -1;
}

// Write the image to a file with a different name,
// using a different image format -- .png instead of .jpg
if( !cvSaveImage("my_image_copy.png", pInpImg) )
{
 fprintf(stderr, "failed to write image file
");
}

// Remember to free image memory after using it!
cvReleaseImage(&pInpImg);

return 0;
}

So during execution, the code builds successfully, but always ends up in the following loop and halts execution:

    if(!pInpImg)
{
 fprintf(stderr, "failed to load input image
");
 return -1;
}

Has anyone faced such a problem before? How could I solve this?

(During installation of 'Macports' and 'Cmake', I had received an alert saying that Xcode was not installed or was installed without 'Command Line Tools'. But as per another thread on this forum, I had installed these from the Xcode-->Preferences-->Downloads folder on installing Xcode. However, still during installation, 'Macports' and 'Cmake' gave me warnings, but installed anyway. But could this be the issue? )

Thank you!

Answer 1

The problem is that you're putting the image into the project folder instead of the folder containing your executable. You can either put the image file in the folder with the executable or put the full path to the image in the call to cvLoadImage.

Older versions of Xcode put the executable in either the build/Debug or build/Release folder in the project folder. Newer versions of Xcode put the build products in the project folder in the DerivedData folder. You can find the DerivedData folder by going to File -> Project Settings… and clicking the arrow next to the folder path: