OpenCV Error: Assertion failed (scn == 3 || scn == 4) in cv:: cvtColor, file ..\..\..\..\opencv\modules\imgproc\src\color.cpp, line 3737

Question

Hi I am trying to run this sample code from OpenCV:

#include "opencv2\opencv.hpp"

using namespace cv;

int main(int, char**)
{
    VideoCapture cap(0); // open the default camera
    if (!cap.isOpened())  // check if we succeeded
        return -1;

    Mat edges;
    namedWindow("edges", 1);
    for (;;)
    {
        Mat frame;
        cap >> frame; // get a new frame from camera
        cvtColor(frame, edges, CV_BGR2GRAY);
        GaussianBlur(edges, edges, Size(7, 7), 1.5, 1.5);
        Canny(edges, edges, 0, 30, 3);
        imshow("edges", edges);
        if (waitKey(30) >= 0) break;
    }
    // the camera will be deinitialized automatically in VideoCapture destructor
    return 0;
}

I am currently using a Windows 7 x64 BootCamp on a Macbook Pro. I'm running this code with Visual Studios 2013 and OpenCV 2.4.9.

This is how I've set up my Config Properties:

VC++ Directories: Include Directories: H:\opencv\build\include;$(IncludePath)

Linker:General:Additional Library Directories: H:\opencv\build\x64\vc12\lib;%(AdditionalLibraryDirectories)
Linker:Input:Additional Dependencies: opencv_calib3d249.lib;opencv_contrib249.lib;opencv_core249.lib;opencv_features2d249.lib;opencv_flann249.lib;opencv_gpu249.lib;opencv_highgui249.lib;opencv_imgproc249.lib;opencv_legacy249.lib;opencv_ml249.lib;opencv_nonfree249.lib;opencv_objdetect249.lib;opencv_ocl249.lib;opencv_photo249.lib;opencv_stitching249.lib;opencv_superres249.lib;opencv_ts249.lib;opencv_video249.lib;opencv_videostab249.lib;%(AdditionalDependencies)

When I click on Local Windows Debugger in Release x64 mode I get the following error from Visual Studios:

First-chance exception at 0x000007FEFD21B3DD in Project3.exe: Microsoft C++ exception: cv::Exception at memory location 0x000000000019A8A0.

If there is a handler for this exception, the program may be safely continued.

When I click Break instead (scared to press Continue), a window named Edges does pop up and the camera does turn on since the green light turns on. But I also get the following error in the command window:

OpenCV Error: Assertion failed (scn == 3 || scn == 4) in cv:: cvtColor, file ........\opencv\modules\imgproc\src\color.cpp, line 3737

I'm pretty new to C++ and Visual Studios, any help would be appreciated. Thanks in advance!

Answer 1

From the conversation in the comments to the question, we saw that VideoCapture gives frame in grayscale. So the call to cvtColor caused the crash.

...
Mat frame;
cap >> frame; // frame is already CV_8UC1
//cvtColor(frame, edges, CV_BGR2GRAY); // so don't to convert here, or crash!
edges = frame.clone(); 
...