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

In fact, if you just want to copy one of the channels or split the color image in 3 different channels, CvSplit() is more appropriate (I mean simple to use).

Mat img(5,5,CV_64FC3);
Mat ch1, ch2, ch3;
// "channels" is a vector of 3 Mat arrays:
vector channels(3);
// split img:
split(img, channels);
// get the channels (dont forget they follow BGR order in OpenCV)
ch1 = channels[0];
ch2 = channels[1];
ch3 = channels[2];