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%Name: Chris Shoemaker%Course: EER-280 - Digital Watermarking%Project: Threshold-Based Correlation in DCT mid-band% Uses two PN sequences; one for a "0" and another for a "1"% Watermark Embeding

clear all;

% save start timestart_time=cputime;

k=20; % set gain factor for embedingblocksize=8; % set the dct blocksize

midband=[ 0,0,0,1,1,1,1,0; % defines the mid-band frequencies of an 8x8dct

0,0,1,1,1,1,0,0;0,1,1,1,1,0,0,0;1,1,1,1,0,0,0,0;

1,1,1,0,0,0,0,0;1,1,0,0,0,0,0,0;1,0,0,0,0,0,0,0;0,0,0,0,0,0,0,0 ];

% read in the cover objectfile_name='cameraman.tif';cover_object=double(imread(file_name));

% determine size of cover imageMc=size(cover_object,1); %HeightNc=size(cover_object,2); %Width

% determine maximum message size based on cover object, and blocksizemax_message=Mc*Nc/(blocksize^2);

% read in the message imagefile_name='rice.png';message=double(imread(file_name));Mm=size(message,1); %HeightNm=size(message,2); %Width

% reshape the message to a vectormessage=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'smessage_vector=ones(1,max_message);message_vector(1:length(message))=message;

% generate shell of watermarked image

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watermarked_image=cover_object;

% read in key for PN generatorfile_name='_key.bmp';key=double(imread(file_name))./256;

% reset MATLAB's PN generator to state "key"rand('state',key);

% generate PN sequencepn_sequence_zero=round(2*(rand(1,sum(sum(midband)))-0.5));

% process the image in blocksx=1;y=1;for(kk = 1:length(message_vector))

% transform block using DCTdct_block=dct2(cover_object(y:y+blocksize-1,x:x+blocksize-1));

% if message bit contains zero then embed pn_sequence_zero into the mid-band

% componants of the dct_blockll=1;if(message_vector(kk)==0)

forii=1:blocksizeforjj=1:blocksize

if(midband(jj,ii)==1)dct_block(jj,ii)=dct_block(jj,ii)+k*pn_sequence_zero(ll);ll=ll+1;

endend

endend

% transform block back into spatial domainwatermarked_image(y:y+blocksize-1,x:x+blocksize-1)=idct2(dct_block);

% move on to next block. At and of row move to next rowif(x+blocksize) >= Nc

x=1;y=y+blocksize;

elsex=x+blocksize;

endend

% convert to uint8 and write the watermarked image out to a filewatermarked_image_int=uint8(watermarked_image);imwrite(watermarked_image_int,'dct2_watermarked.bmp','bmp');

% display processing timeelapsed_time=cputime-start_time,

% display psnr of watermarked image

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psnr=psnr(cover_object,watermarked_image,Nc,Mc),

% display watermarked imagefigure(1)imshow(watermarked_image,[])title('Watermarked Image')