dct1_recover.m

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%Name:		Chris Shoemaker
%Course:	EER-280 - Digital Watermarking
%Project: 	Block DCT Based method, using comparision between mid-band coeffcients
%           Watermark Recovery

clear all;

% save start time
start_time=cputime;

blocksize=8;    % set the size of the block in cover to be used for each bit in watermark

% read in the watermarked object
file_name='dct1_watermarked.bmp';
watermarked_image=double(imread(file_name));

% determine size of watermarked image
Mw=size(watermarked_image,1);	        %Height
Nw=size(watermarked_image,2);	        %Width

% determine maximum message size based on cover object, and blocksize
max_message=Mw*Nw/(blocksize^2);

% read in original watermark
file_name='_copyright.bmp';
orig_watermark=double(imread(file_name));

% determine size of original watermark
Mo=size(orig_watermark,1);	%Height
No=size(orig_watermark,2);	%Width

% process the image in blocks
x=1;
y=1;
for (kk = 1:max_message)

    % transform block using DCT
    dct_block=dct2(watermarked_image(y:y+blocksize-1,x:x+blocksize-1));
    
    % if dct_block(5,2) > dct_block(4,3) then message(kk)=0
    % otherwise message(kk)=1
    if dct_block(5,2) > dct_block(4,3)
        message_vector(kk)=0;
    else
        message_vector(kk)=1;
    end
 
    % move on to next block. At and of row move to next row
    if (x+blocksize) >= Nw
        x=1;
        y=y+blocksize;
    else
        x=x+blocksize;
    end
end

% reshape the embeded message
message=reshape(message_vector(1:2000),40,50);

% display processing time
elapsed_time=cputime-start_time,

% display recovered message
figure(2)
imshow(message,[])
title('Recovered Message')