Opencv Unhandled exception in contour.exe

Question

My code in OpenCV works well up until when I want to find contours:

findContours(src, contours,hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE);

then I keep getting the following error:

"Unhandled exception at 0x773e3e28 in Contour.exe: Microsoft C++ exception: cv::Exception at memory location 0x002ff3ac.."

Do you have any idea about this error?

My full code is below.

Thanks

Mat src=Mat(100,200,CV_64F),newimg;
vector<vector<Point>> contours;
vector<Vec4i> hierarchy;

for (int i=25;i<80;i++)
    for(int j=25;j<80;j++)
        src.at<double>(i,j)=1;
imshow("img",src);
waitKey(0);

findContours(src, contours,hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE);

Answer 1

Quoting from OpenCV documentation about findContours

image – Source, an 8-bit single-channel image. Non-zero pixels are treated as 1’s. Zero pixels remain 0’s, so the image is treated as binary . You can use compare() , inRange() , threshold() , adaptiveThreshold() , Canny() , and others to create a binary image out of a grayscale or color one. The function modifies the image while extracting the contours. If mode equals to CV_RETR_CCOMP or CV_RETR_FLOODFILL, the input can also be a 32-bit integer image of labels (CV_32SC1).

You can adjust your code converting your CV_64FC1 image to a CV_8UC1 like:

...
Mat1b img8u;
src.convertTo(img8u, CV_8U);

vector<vector<Point>> contours;
vector<Vec4i> hierarchy;

findContours(img8u, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE);
...

---

In addition, from the comments turns out that you are using Visual Studio 2010, but linking OpenCV built with msvc11 (Visual Studio 2012).

You need either to use Visual Studio 2012, or recompile OpenCV with msvc10 (Visual Studio 2010). If you decide to upgrade VS, you can go directly to VS2013 (and link to vc12), or to VS2015 (but you need to recompile OpenCV as well).