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

You can use split function and then put zeros to the channels u want to ignore. This will result dispalying one channels out of three. See below..

For example:

Mat img, chans[3]; 
img = imread(.....);  //make sure its loaded with an image

//split the channels in order to manipulate them
split(img, chans);

//by default opencv put channels in BGR order , so in your situation you want to copy the first channel which is blue. Set green and red channels elements to zero.
chans[1]=Mat::zeros(img.rows, img.cols, CV_8UC1); // green channel is set to 0
chans[2]=Mat::zeros(img.rows, img.cols, CV_8UC1);// red channel is set to 0

//then merge them back
merge(chans, 3, img);

//display 
imshow("BLUE CHAN", img);
cvWaitKey();