% image downloaded from www.math.uic.edu
x = imread('My Documents/Bean.jpg');

% the image we just downloaded is stored
% as a matrix
size(x)

ans =

   200   300     3

image(x)
% let us remove the blue
noblue = x;
noblue(:,:,3) = zeros(size(x,1),size(x,2));
image(noblue)
% to compute with the values, we must convert
% the rgb encoding into doubles
% every rgb code is stored as one byte
dx = double(x);
% let us increase the blue intensity
moreblue = dx;
moreblue(:,:,3) = dx(:,:,3)*1.5;
% image does not take a matrix of
% doubles on input, we must convert again
% but now to uint8
y = uint8(moreblue);
figure
image(y)
% we could create a new image,
% selecting half of the rows from noblue
% and the other half of from moreblue
z = y;
z(1:size(z,1)/2,:,:) = noblue(1:size(z,1)/2,:,:);
figure
image(z)
edit
help crypto
  blurs or deblurs an image

blur = randn(size(x,1));
key = inv(blur);
bx = crypto(blur,double(dx));
figure
image(uint8(bx))
dbx = crypto(key,bx);
figure
image(uint8(dbx))
diary off