数字水印综述加代码,具有很重要的参考价值

%Name: Chris Shoemaker %Course: EER-280 - Digital Watermarking %Project: Comparison-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 time start_time=cputime; k=15; % set gain factor for embeding blocksize=8; % set the dct blocksize pn_sequence_search='T'; % perform search to find highly uncorrelated pn sequences {T,F} midband=[ 0,0,0,1,1,1,1,0; % defines the mid-band frequencies of an 8x8 dct 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 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's message_vector=ones(1,max_message); message_vector(1:length(message))=message; % generate shell of watermarked image watermarked_image=cover_object; % read in key for PN generator file_name='_key.bmp'; key=double(imread(file_name))./256; % reset MATLAB's PN generator to state "key" rand('state',key); % generate PN sequences for "1" and "0" pn_sequence_one=round(2*(rand(1,sum(sum(midband)))-0.5)); pn_sequence_zero=round(2*(rand(1,sum(sum(midband)))-0.5)); % find two highly un-correlated PN sequences if (pn_sequence_search=='T') while (corr2(pn_sequence_one,pn_sequence_zero) > -0.55) pn_sequence_one=round(2*(rand(1,sum(sum(midband)))-0.5)); pn_sequence_zero=round(2*(rand(1,sum(sum(midband)))-0.5)); end end % process the image in blocks x=1; y=1; for (kk = 1:length(message_vector)) % transform block using DCT dct_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_block ll=1; if (message_vector(kk)==0) for ii=1:blocksize for jj=1:blocksize if (midband(jj,ii)==1) dct_block(jj,ii)=dct_block(jj,ii)+k*pn_sequence_zero(ll); ll=ll+1; end end end % otherwise, embed pn_sequence_one into the mid-band componants of dct_block else for ii=1:blocksize for jj=1:blocksize if (midband(jj,ii)==1) dct_block(jj,ii)=dct_block(jj,ii)+k*pn_sequence_one(ll); ll=ll+1; end end 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,'dct2_watermarked_mod.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')