OpenCV2.3での白黒変換

rgb2gray.cpp

#include <opencv/cv.h>
#include <opencv/highgui.h>

using namespace cv;
int main(int argc, char** argv)
{
  const char *imagename = argc > 1 ? argv[1] : "../image/hoge.png";
  Mat src_img = imread(imagename);
  if(!src_img.data)
    return -1;
  Mat gray_img;
  cvtColor(src_img,gray_img, CV_BGR2GRAY);
 
  imwrite("gray.png",gray_img);
  return 0;
}