Unsupported depth in Opencv - c++

Question

I am trying to learn some basics, but I keep getting errors.
I am trying to resize a cv::Mat
Edit to clarify why I am not loading an image: I am trying to test without having access to external files.
Inside the code, though, I put int x = M.depth(); and it read 0
cv::Mat M(2,2, CV_8UC3, cv::Scalar(0,0,255));
scale = 2;
cv::Size myImageSize;
myImageSize.height = M.rows;
myImageSize.width = M.cols;
cv::Mat ImgCopy = cvCreateImage(myImageSize, M.depth(), M.channels());
..
cv::resize(M, ImgCopy, myImageSize, 0, 0, CV_INTER_LINEAR);
I am getting an error on the line cvCreateImage
Input image depth is not supported by function (Unsupported format) in unknown functio, file... \modules\core\src\array.cpp...
I have tried with other values (CV_32F...) and I get the same error.
Please help !

Answer 1

cvCreateImage() is for use with the C API and returns an IplImage*. To initialize a cv::Mat, use the appropriate constructor.
cv::Mat ImgCopy(M.size(), M.type());
is the most succinct way to create and allocate memory for a new cv::Mat.
However, cv::resize() makes it even easier. You just have to declare your image
cv::Mat ImgCopy
and the arguments to cv::resize() allow automatic calculation of the correct dimensions and type. The last three parameters do not need to be specified because you don't change them from the defaults.
cv::resize(M, ImgCopy, myImageSize);

Answer 2

Try this code :
using namespace cv;
using namespace std;
int main( int argc, char** argv )
{
IplImage *src,*dst;
src=cvLoadImage("img.png");
cvNamedWindow("SRC", CV_WINDOW_AUTOSIZE);
cvNamedWindow("DST", CV_WINDOW_AUTOSIZE);
dst = cvCreateImage(cvSize(500,500),src->depth,src->nChannels);
cvResize(src,dst);
cvShowImage("SRC",src);
cvShowImage("DST",dst);
cvWaitKey(0);
cvDestroyWindow("SRC");
cvDestroyWindow("DST");
cvReleaseImage(&dst);
cvReleaseImage(&src);
return 0;
}