数字水印技术DCT算法MATLAB源代码

%Name: Chris Shoemaker

%Course: E ER-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_std_bw.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