You can read in an image file with imread(). That will get you ALL the image pixel values without having to click on anything.
rgbImage = imread(fullFileName);
To split apart an RGB image into the individual color channels, you can do this:
% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
To recombine them into an RGB image again, do this:
% Recombine separate color channels into a single, true color RGB image.
rgbImage = cat(3, redChannel, greenChannel, blueChannel);
