Access to each separate channel in OpenCV

Question

I have an image with 3 channels (img) and another one with a single channel (ch1).

    Mat img(5,5,CV_64FC3);
    Mat ch1 (5,5,CV_64FC1);

I

Answer 1

There is a function called cvMixChannels. You'll need to see implementation in the source code, but I bet it is well optimized.