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error while drawing lines from houghlines()

asked 2015-11-14 21:23:31 -0600

angel2008 gravatar image

updated 2015-11-15 09:22:25 -0600

hi guys, im new to openCv and image processing in general and i need to draw the lines in real time from a camera input. it working fine until i try to draw in the original image the lines detected with houghlines(). here is my code:

int main(int argc, char* argv[])
    Mat input;
    Mat HSV;
    Mat threshold;
    Mat CannyThresh;
    Mat HL;

    //video capture object to acquire webcam feed
    cv::VideoCapture capture;;
    capture.set(CV_CAP_PROP_FRAME_WIDTH, 640);
    capture.set(CV_CAP_PROP_FRAME_HEIGHT, 480);

    //start an infinite loop where webcam feed is copied to cameraFeed matrix
    //all operations will be performed within this loop

    while (true){ ;
        cvtColor(input, HSV, COLOR_BGR2HSV); //hsv
        inRange(HSV, Scalar(H_MIN, S_MIN, V_MIN), Scalar(H_MAX, S_MAX, V_MAX), threshold);//thershold
        MorphOps(threshold);//morph operations on threshold image
        Canny(threshold, CannyThresh, 100, 50); //canny edge detection

        std::vector<Vec4i> lines;
        HoughLines(CannyThresh, lines, 1, CV_PI/180, 150, 0, 0 );

        for( size_t i = 0; i < lines.size(); i++ )
            float rho = lines[i][0], theta = lines[i][1];
            Point pt1, pt2;
            double a = cos(theta), b = sin(theta);
            double x0 = a*rho, y0 = b*rho;
            pt1.x = cvRound(x0 + 1000*(-b));
            pt1.y = cvRound(y0 + 1000*(a));
            pt2.x = cvRound(x0 - 1000*(-b));
            pt2.y = cvRound(y0 - 1000*(a));
            line( input, pt1, pt2, Scalar(0,0,255), 3, CV_AA);

        imshow("camera", input);

return 0;

im getting the following exception:

First-chance exception at 0x74DB3E28 in Proyecto0.1.exe: Microsoft C++ exception: cv::Exception at memory location 0x00D6F47C.

i know the error is happening in the

for( size_t i = 0; i &lt; lines.size(); i++ )

line because if i comment everything inside the for loop, i still get the same error, but if i remove the whole for-loop, it doesnt throws the exception. any ideas of what may be happening?

EDIT #1 the debugger doesn't throw any errors. but in the console of the program it says OpenCV Error:Assertion failed (channels() == CV_MAT_CN(dtype)) in cv::Mat::copyTo, file C:\builds\master_packSlave-Win32-vc12-shared\opencv\modules\core\src\copy.cpp, line 281. Also the last call in the call stack is this: > KernelBase.dll!_RaiseException@16() Unknown, im starting to thing is an opencv problem and not a code problem, maybe something with that dll.

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answered 2015-11-15 09:53:11 -0600

//std::vector<Vec4i> lines; // this line causes exception
std::vector<Vec2f> lines; // right usage

you can find an example usage here

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thank you for your response. i changed what you said, and now it enters the for loop. but i get another segmentation fault. in the auto variables windows on visual studio i see that the values of the variables i, lines.size, rho and theta are a little odd when it throws the exception: i=19470, lines.size=534760974, rho =2.42330915e-038, theta = 0.000000 any other idea?

angel2008 gravatar imageangel2008 ( 2015-11-15 10:37:49 -0600 )edit

i think you must to check your Visual Studio configuration. ( sorry i am using Code::Block and don't know about VS)

sturkmen gravatar imagesturkmen ( 2015-11-15 10:55:56 -0600 )edit

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Asked: 2015-11-14 21:23:31 -0600

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Last updated: Nov 15 '15