www.pudn.com > 953893dct1_embed.rar > dct1_embed.m

%Name:		Chris Shoemaker 
%Course:	EER-280 - Digital Watermarking 
%Project: 	Block DCT Based method, using comparision between mid-band coeffcients 
%           Watermark Embeding 
 
clear all; 
 
% save start time 
start_time=cputime; 
 
k=50;           % set minimum coeff difference 
blocksize=8;    % set the size of the block in cover to be used for each bit in watermark 
 
% read in the cover object 
file_name='lena.bmp'; 
cover_object=double(imread(file_name)); 
 
% determine size of cover image 
Mc=size(cover_object,1);	        %Height 
Nc=size(cover_object,2);	        %Width 
 
% determine maximum message size based on cover object, and blocksize 
max_message=Mc*Nc/(blocksize^2); 
 
% read in the message image 
file_name='_copyright.bmp'; 
message=double(imread(file_name)); 
Mm=size(message,1);	                %Height 
Nm=size(message,2);	                %Width 
 
% reshape the message to a vector 
message=round(reshape(message,Mm*Nm,1)./256); 
 
% check that the message isn't too large for cover 
if (length(message) > max_message) 
    error('Message too large to fit in Cover Object') 
end 
 
% pad the message out to the maximum message size with ones 
message_pad=ones(1,max_message); 
message_pad(1:length(message))=message; 
 
% generate shell of watermarked image 
watermarked_image=cover_object; 
 
% process the image in blocks 
% encodes such that (5,2) > (4,3) when message(kk)=0 
% and that (5,2) < (4,3) when message(kk)=1 
x=1; 
y=1; 
for (kk = 1:length(message_pad)) 
 
    % transform block using DCT 
    dct_block=dct2(cover_object(y:y+blocksize-1,x:x+blocksize-1)); 
     
    % if message bit is black, (5,2) > (4,3) 
    if (message_pad(kk) == 0) 
 
        % if (5,2) < (4,3) then we need to swap them 
        if (dct_block(5,2) < dct_block(4,3)) 
                temp=dct_block(4,3); 
                dct_block(4,3)=dct_block(5,2); 
                dct_block(5,2)=temp; 
        end 
     
    % if message bit is white, (5,2) < (4,3) 
    elseif (message_pad(kk) == 1) 
         
        % if (5,2) > (4,3) then we need to swap them 
        if (dct_block(5,2) >= dct_block(4,3)) 
                temp=dct_block(4,3); 
                dct_block(4,3)=dct_block(5,2); 
                dct_block(5,2)=temp; 
        end 
    end 
     
    % now we adjust the two values such that their difference >= k 
    if dct_block(5,2) > dct_block(4,3) 
        if dct_block(5,2) - dct_block(4,3) < k 
            dct_block(5,2)=dct_block(5,2)+(k/2); 
            dct_block(4,3)=dct_block(4,3)-(k/2);             
        end 
    else   
         if dct_block(4,3) - dct_block(5,2) < k 
            dct_block(4,3)=dct_block(4,3)+(k/2);   
            dct_block(5,2)=dct_block(5,2)-(k/2); 
        end 
    end 
         
    % transform block back into spatial domain 
    watermarked_image(y:y+blocksize-1,x:x+blocksize-1)=idct2(dct_block);     
     
    % move on to next block. At and of row move to next row 
    if (x+blocksize) >= Nc 
        x=1; 
        y=y+blocksize; 
    else 
        x=x+blocksize; 
    end 
end 
 
% convert to uint8 and write the watermarked image out to a file 
watermarked_image_int=uint8(watermarked_image); 
imwrite(watermarked_image_int,'dct1_watermarked.bmp','bmp'); 
 
% display processing time 
elapsed_time=cputime-start_time, 
 
% display psnr of watermarked image 
psnr=psnr(cover_object,watermarked_image,Nc,Mc), 
 
% display watermarked image 
figure(1) 
imshow(watermarked_image,[]) 
title('Watermarked Image')