dct88.m

基于dct的数字水印算法

function []=dct88(o,c,w)
%Name:                    Digital Watermarking Embeding Algorithms Based On 8*8 Block DCT
%Programmer:              Chen Ning
%Algorithms Description:  8*8 Block DCT Based Method:using comparision between mid-band coeffcients
%                         Watermark Embeding

dif=50;           % set minimum coefficient difference
blocksize=8;    % set the size of the block in order to be used for each bit in watermark

% read in the original image
file_name = o ;
ori_img=double(imread(file_name));

% calculate the size of original image
Mc=size(ori_img,1);	        %height of original image
Nc=size(ori_img,2);	        %width of original image

% calculate the maximum size of message that can be embeded in the original image
max_message=Mc*Nc/(blocksize^2);

% read in the original watermarking image
file_name = c;
message=double(imread(file_name));
% calculate the size of original watermarking image
Mm=size(message,1);	                %height of watermarking image
Nm=size(message,2);	                %width of watermarking image

% reshape the message to a vector with one row and Mm*Nm columns
message=message';
message=reshape(message,1,Mm*Nm);
message_pad=message;

% check if the message is too large for original image
if (length(message) > max_message)
    error('Message too large for original image!')
end

% pad the message out to the maximum message size with ones
message=(ones(1,max_message))';

% generate shell of watermarked image
watermarked_image=ori_img;

% divide the original image into blocks with size of 8*8
% if message(k)=0 adjust the DCT coefficient to make sure that (5,2)>(4,3) 
% if message(k)=1 adjust the DCT coefficient to make sure that (5,2)<(4,3) 
i=1;
j=1;
for (k = 1:max_message)

    % make DCT transformation for each 8*8 blocks
    dct_block=dct2(ori_img(j:j+blocksize-1,i:i+blocksize-1));
    
    % if message bit is black, make sure that (5,2)>(4,3) 
    if (message_pad(k) == 0)
        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, make sure that (5,2)<(4,3) 
    elseif (message_pad(k) == 1)
        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
    
    % adjust the two values to make such that their difference is larger than 'dif'
    if dct_block(5,2) > dct_block(4,3)
        if dct_block(5,2) - dct_block(4,3) < dif
            dct_block(5,2)=dct_block(5,2)+(dif/2);
            dct_block(4,3)=dct_block(4,3)-(dif/2);            
        end
    else  
    if dct_block(4,3) - dct_block(5,2) < dif
            dct_block(4,3)=dct_block(4,3)+(dif/2);  
            dct_block(5,2)=dct_block(5,2)-(dif/2);
        end
    end
    
    % transform 8*8 DCT block back into spatial domain
    watermarked_image(j:j+blocksize-1,i:i+blocksize-1)=idct2(dct_block);    
    
    % at the end of a row ,move on to the next row
    if (i+blocksize) >= Nc
        i=1;
        j=j+blocksize;
    % move on to the next 8*8 block in the same row
    else
        i=i+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,w,'bmp');

%display watermarked image
figure(1)
imshow(watermarked_image,[])
title('Watermarked Image')
figure(2)
imshow(ori_img,[])
title('Original Image')