I=imread('flower.jpg');       % convert the JPG image file into a matrix.

I=double(I);     % convert the unsigned integer matrix to a double precision matrix 
J=255*ones(size(I))-I; % this operation inverts the image intensities
J=uint8(J); % convert back to an unsigned integer matrix
imwrite(J,'ivflower.jpg','jpg'); % convert the matrix into a JPG image file

% plot out the original image and the inverted image.
colormap(gray);             
subplot(2,1,1),imagesc(I);   % Subplot: creates axes in tiled positions.
title('Original Image')
subplot(2,1,2),imagesc(J);   % Imagesc: scales data and displays as image.
title('Inverted Image')