This code sample will draw a red circle on a white background. using the ColorConversionCodes COLOR_GRAY2RGB marker, the color identity Scalar(0,0,255) produces red. why not blue? Does the circle function convert the color code back to BGR?
#include <opencv2/opencv.hpp>
using namespace cv;
int main(int argc, char ** argv){
Mat md0, md1, md2;
md0 = Mat::zeros(200,400,CV_32F);
md1 = Mat::ones(200,400,CV_32F);
//drawing function
Point2f p(77, 100);
cvtColor(md1, md2, COLOR_GRAY2RGB );
circle( md2, p,50,Scalar(0,0,255),2,8,0);
imshow("MD2", md2);
waitKey(0);
return 0;
}