Suppose your image size is 50*50, then u separate each RGB plane.
R=image(:,:,1); or R=image(1:50,1:50,1);
G=image(:,:,2); or G=image(1:50,1:50,2);
B=image(:,:,3); or B=image(1:50,1:50,3);
by varying row and column of each plane you can check pixel values.
I hope this is answer for your question.