3.将彩色图片转换为灰度图片

void Test_ConvertColor()
{
	Mat g_srcImage=imread("D:\\OpenCV Projects\\OpenCV_Test_Image\\5.jpg");
	Mat g_tmpImage_Gray,g_tmpImage_BGRA;
	cvtColor(g_srcImage,g_tmpImage_Gray,CV_BGR2GRAY);
	cvtColor(g_srcImage,g_tmpImage_BGRA,CV_BGR2BGRA);
	imshow("CV_BGR2BGRA",g_tmpImage_BGRA);
	imshow("CV_BGR2GRAY",g_tmpImage_Gray);
	imshow("原图",g_srcImage);
}

CV_BGR2GRAY这个参数决定了要转换什么样的图片，源代码中有定义，可以追溯查看。

/* Constants for color conversion */
enum
{
    CV_BGR2BGRA    =0,
    CV_RGB2RGBA    =CV_BGR2BGRA,
    CV_BGRA2BGR    =1,
    CV_RGBA2RGB    =CV_BGRA2BGR,
    CV_BGR2RGBA    =2,
    CV_RGB2BGRA    =CV_BGR2RGBA,
    CV_RGBA2BGR    =3,
    CV_BGRA2RGB    =CV_RGBA2BGR,
    CV_BGR2RGB     =4,
    CV_RGB2BGR     =CV_BGR2RGB,
    CV_BGRA2RGBA   =5,
    CV_RGBA2BGRA   =CV_BGRA2RGBA,
    CV_BGR2GRAY    =6,
    CV_RGB2GRAY    =7,
    CV_GRAY2BGR    =8,
    CV_GRAY2RGB    =CV_GRAY2BGR,
    CV_GRAY2BGRA   =9,
    CV_GRAY2RGBA   =CV_GRAY2BGRA,
    。。。。。。