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
% 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')。