Difficulty in getting the matrix of red, green,blue

 a = imread('Sample1.jpg');
 imshow(a)

This gives me the image but my problem is stated as below

It happens that I have an image in RGB format then how to get 3 different matrix of red ,green,blue respectively in Mat lab , I have also searched the documentation but can't get satisfactory reply , I also want to store this values.

via Chebli Mohamed