signed_mat2dceb.m

基于图象的数据隐写和提取matlab代码

function B=signed_mat2DCEB(N,t);
%This takes a picture matrix of magnitudes N and a threshold t the
%matrix is then broken up into 8x8 tiles then transformed using the DCT
%the results are rounded for a slight quantitization.
%this method does not give exact compression ratios, but the compression
%occurs more in the less significant frequencies rather than across the
%entire range of coefficents
%here the "dropped coefficents" are temporarily set to 1 with the same
%sign they orignally had. This marks them for replacement with data using
%the zeros hiding method
%
%
%Please input a square matrix that has multiple of 8 dimensions
[x dnk]=size(N);
x1=x/8;

tiled=zeros(8,8,x1,x1);

q=qmat();

%break up the matrix into 8x8 tiles and quantize
for i=1:x1
    for j=1:x1
        tiled(:,:,i,j)=round(dct2(N(8*i-7:i*8,8*j-7:j*8)));
    end
end



%marks coefficients at or below the threshold value with a one
%it keeps the sign of the original coefficent so that the zeros
%data will won't be as noticiable
[dnk dnk x x]=size(tiled);
keeps= x^2*8^2;
drops=0;
for i=1:x
    for j=1:x
        for m=1:8
            for n=1:8
                if (abs(tiled(m,n,i,j))<=t && abs(tiled(m,n,i,j))>0)
                    if(tiled(m,n,i,j)>0)
                        tiled(m,n,i,j)=1;
                    else
                        tiled(m,n,i,j)=-1;
                    end    
                    drops=drops+1;
                    
                end
            end
        end
    end
end
keeps=keeps-drops;
sprintf('drops=%d',drops)
sprintf('keeps=%d',keeps)
B=tiled;