Color Conversion

// CV_BGR2GRAY, CV_BGR2HSV, CV_BGR2YCrCb, CV_BGR2Lab, ......
cvtColor(image, image_YUV, CV_BGR2YUV);

Split / Merge

Mat yuv_channels[3];
split(image_YUV, yuv_channels);
merge(yuv_channels, 3, dst);

imshow("input image", image); 
imshow("Y", yuv_channels[0]); 
imshow("U", yuv_channels[1]); 
imshow("V", yuv_channels[2]); 
imshow("YUV image", dst);