%How to read, display, and write an image
A = imread('SITE.tif');   %reads the image into a byte array (uint8) the size of the image
                          % with values between 0 and 255
B = im2double(A);    % converts to a real array (double) with values between 0 and 1
                     % this is the preferred format to do calculations
C = im2double(imread('SITE.tif'));  % in one step                     
figure, imshow(A)  % display A in a figure window
figure, imshow(B)  % display B in a new figure window. imshow works for both uint8 and double
figure, imshow(C)  % should be the same as B
D = 1 - C;   %compute negative image
figure, imshow(D)
imwrite(D, 'SITE_negative.tif') %   write a matrix representing a valid image to a TIFF image file