prova.m

simple watermark test

% DCT-based image watermarking
% Digital watermarking has been proposed as a viable solution
% to the need of copyright protection and authentication
% of multimedia data in a networked environment, since
% it makes possible to identify the author, owner, distributor
% or authorized consumer of a document. In this paper a new
% watermarking technique to add a code to digital images is
% presented: the method operates in the frequency domain
% embedding a pseudo-random sequence of real numbers in a
% selected set of DCT coeficients. Watermark casting is performed
% by exploiting the masking characteristics of the Human
% Visual System, to ensure watermark invisibilily. The
% embedded sequence is extracted without resorting to the
% original image, so that the proposed technique represents
% a major improvement to methods relying on the comparison
% between the watermarked and original images. Experimental
% results demonstrate that the watermark is robust to
% most of the signal processing techniques and geometric distortions.
%
% For the complete source code please visit
% http://www.advancedsourcecode.com/dctwater.asp
% 
% For more information please email me [e-mail]
%
% References
% A. Piva, M. Barni, F. Bartolini, and V. Cappellini,
% "DCT-based watermark recovering without restoring
% to the uncorrupted original image", in International
% Conference on Image Processing, vol. 111, pp. 520-523, 1997.
% This article is available at
% http://www.tsi.enst.fr/~maitre/tatouage/icip97/piva-97.pdf
%
% 
% Luigi ROSA
% Via Centrale 35
% 67042 Civiata Di Bagno
% L'Aquila - ITALY
% mobile [phone]
% email [e-mail]
% website http://www.advancedsourcecode.com
%

clc;clear;close all;

enablevisualization = 1; % this parameter enables visualization of images

img  = imread('v17.jpg');  % image acquisition
img  = rgb2gray(img);      % image is converted from RGB to GRAYSCALE. Not necessary
                           % if the input image is grayscale.
img0 = img;
img  = double(img); % input grayscale image

L    = 25000;       % the lowest L coefficients that are skipped (see the cited article)
M    = 16000;       % the length of the watermark (see the cited article)



x = randn(M,1);     % the watermark has a normal distribution (pseudo-random sequence)
visualmasking = 1;  % the visual masking option. If 1 it is enabled.


alfa = 6.2;   % if visualmasking is enabled (1) alfa has to be greater (6.2 is a good value).
              % Otherwise (visualmasking is not enabled 0) a good value for alfa is 0.2. 
              % In the first case (visual masking enabled) the effective value of alfa is alfa_new = alfa_old * factor 
              % (see the cited article for more details). In the second case
              % (visual masking not enabled) the value of alfa has NOT to
              % be changed.
R    = 9;     % the window of the square block size for the computation of variance
              % when the visual masking is enabled. If visualmasking = 0
              % this value is not used.

% the watermarked image is calculated. If visual masking (visualmasking) is enabled
% a new value for the alfa has to be considered. Otherwise the value
% of alfa is not changed.
[watermarked_image,alfa]  = wm_casting(img,x,L,alfa,R,visualmasking);
% Watermark casting
% [watermarked_image,alfa] = wm_casting(img,x,L,alfa,R,visualmasking)
% img:                   input image
% x:                     watermark whisch has to be added to the image
% L:                     skipped DCT coefficients
% alfa:                  watermarking parameter
% R:                     block size (if viasual masking is enabled)
% visualmasking:         if 1 the visual masking is enabled
%                        image
% watermarked_image:     watermarked image
% alfa:                  the new value of alfa (if visual masking is not
%                        enable this value is not changed)
%
% watermarked_image is the watermarked image

% NOTE: the watermarked image can be saved as a grayscale image (uint8
% type). In fact it is not necessary that the watermarkled image is a
% double matrix.
watermarked_image = double(uint8(watermarked_image));

if enablevisualization
    % visualization
    figure('Name','Input grayscale image');
    imshow(img0);
    pause(0.3);
    
    figure('Name','Watermarked image');
    imshow(uint8(watermarked_image));
    pause(0.3);
    
    figure('Name','Different pixels');
    imshow(watermarked_image~=img0);
    pause(0.3);
end
% image degradation
% ...
% ...
%corrupted_image = watermarked_image;                                          % if no noise is introduced
corrupted_image = double(watermarked_image)+130*rand(size(watermarked_image)); % if some noise is introduced
% now the watermarked image is corrupted by noise
% ...
% ...
if enablevisualization
    % visualization
    figure('Name','Corrupted image');
    imshow(uint8(corrupted_image));
    pause(0.3);     
end
% the correct watermark (it should be revealed)
[z,Sz]                       = wm_detection(corrupted_image,x,L,alfa);
% Watermark detection
% [z,Sz] = wm_detection(watermarked_image,x,L,alfa)
% watermarked_image:     input, watermarked (and evantually corrupted)
%                        image
% x:                     watermark
% L:                     number of initial skipped coefficients
% alfa:                  watermarking parameter
% z:                     computed correlation
% Sz:                    thereshold correlation. If z >= Sz the watermarked
%                        image was created using x vector





% a wrong watermark (it should not be revealed)
%[z,Sz]                       = wm_detection(corrupted_image,randn(size(x)),L,alfa);




% results: the corruped image is the watermarked image?
disp('Test results:');
if z >= Sz
    disp('Watermarked image');
else
    disp('Non-watermarked image');
end
disp('* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *');
disp('For the complete source code please visit');
disp('http://www.advancedsourcecode.com/dctwater.asp');
web http://www.advancedsourcecode.com/dctwater.asp