MATLAB: How to calculate a digital value of a band in hyperspectral image

digital value

please help

I = imread('landsat.jpg') ;
R = I(:,:,1) ;
G = I(:,:,2) ;
B = I(:,:,3) ;

I = imread(image) ;
R = I(:,:,1) ;
G = I(:,:,2) ;
B = I(:,:,3) ;

Read the image using imread or geotifread as regular Let's say i issued:

I=imread('satimage.tif');

then I is of size MxNx4

Then each band can be simply separated as:

Band1=I(:,:,1);
Band2=I(:,:,2);
Band3=I(:,:,3);
Band4=I(:,:,4);