creating a grayscale video using opencv - c++

Question

I need to save a grayscale video from a GIge camera using OpenCV on Mac os X 10.8. I used this code:
namedWindow("My video",CV_WINDOW_AUTOSIZE);
Size frameSize(659, 493);
VideoWriter oVideoWriter ("MyVideo.avi",-1, 30, frameSize, false);
While(1)
{
...
Mat Image=Mat(Size(GCamera.Frames[Index].Width,GCamera.Frames[Index].Height),CV_8UC1,GCamera.Frames[Index].ImageBuffer);
oVideoWriter.write(Image);
...
}
I got this error:
OpenCV Error: Assertion failed (scn == 3 || scn == 4) in cvtColor, file /Users/rosa/OpenCV-2.4.3/modules/imgproc/src/color.cpp, line 3270
libc++abi.dylib: terminate called throwing an exception
The program has unexpectedly finished.

Answer 1

I made it this way:
VideoWriter oVideoWriter ("MyVideo.avi",CV_FOURCC('M','J','P','G'), 30, frameSize);
While(1)
{
Mat Image=Mat(Size(GCamera.Frames[Index].Width,GCamera.Frames[Index].Height),CV_8UC1,GCamera.Frames[Index].ImageBuffer);
Mat colorFrame;
cvtColor(Image, colorFrame, CV_GRAY2BGR);
oVideoWriter.write(colorFrame);
}

Answer 2

Your issue is your operating system. Checking the documentation, it says the greyscale feature is supported on Windows only.
Easy enough fix though,
cv::Mat imageGrey;
cv::Mat imageArr[] = {Image, Image, Image};
cv::merge(imageArr, 3, imageGrey);
oVideoWriter.write(imageGrey);