OpenCV imshow not displaying image in osx

Question

I'm working right out of a book, and copied the following code (essentially the openCV equivalent of "hello world"):

//helloCV.cpp
#include <opencv2/opencv.hpp>

int main(int argc, char** argv){

        cv::Mat img = cv::imread(argv[1], -1);
        if (img.empty()) return -1;

        cv::namedWindow("Example1", cv::WINDOW_AUTOSIZE);
        cv::imshow("Example1", img);
        cv::waitKey(0);
        cv::destroyWindow("Example1");

        return 0;

}//main 

Unfortunately, when I run this code, I get a window with the header and nothing in it:

I suspect that I've messed up the environment or some such when installing OpenCV, but cmake is throwing no errors, and the code runs as expected, exiting correctly on a keystroke and all of that, with the glaring exception of a lack of a displayed photo.

Any tips?

Thanks!

Answer 1

Thanks to @DanMašek for the lead on this one, and to all the people on this page: http://answers.opencv.org/question/160201/video-window-not-loading-frame/

To repeat what they said, what worked for me was the following:

To resolve this, locate the file window_cocoa.mm; if built from source it'll be in opencv/modules/highgui/src.

Change the following:

@implementation CVView
#if defined(__LP64__)
@synthesize image;
#else // 32-bit Obj-C does not have automatic synthesize
@synthesize image = _image;
#endif

To this:

@implementation CVView
@synthesize image = _image;

Do the same thing for the CVWindow and CVSlider implementations to accommodate videos as well.

Recompile OpenCV and test out your code.

Hope this helps other people struggling with this issue!