Opencv Unhandled exception in contour.exe - opencv

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).

Answer 2

Your problem is you are giving "findContours" a CV_64F image when it requires a CV_8UC1 image. You generally pass findContours the output of an edge detector. (E.G. Canny).
If you modify your code to the following you can find the contours in an image after filtering it through Canny.
Mat src=Mat(100,200,CV_64F),newimg;
Mat tCannyMat;
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);
int lowThreshold = 0x3f;//This is the single value threshold
int ratio = 3;//This is the ratio to apply for the entire pixel
int kernel_size = 3;//This is the canny kernel size
//You can use your own edge detector/a different one here if you wish.
//Canny merely serves to give a working example.
cv::Canny( src, tCannyMat, lowThreshold, lowThreshold*ratio, kernel_size );
findContours(tCannyMat, contours,hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE);