基于小波变换的数字水印提取算法 (MATLAB)

function rw = wm_extr(J)
% 此函数为提取过程
% 输入：J为水印嵌入的图像；
% 输出：rw为提取的水印

%%
% 一层小波分解
[LL,LH,HL,HH] = dwt2(J,'haar');
%=======计算avr_LH======
[m,n] = size(LH); avr_LH = 0;
for i = 1:m
    for j = 1:n
        avr_LH = avr_LH + LH(i,j);
    end
end
avr_LH = avr_LH / (m*n);

%=======计算avr_HL======
[m0,n0] = size(HL); avr_HL = 0;
for i = 1:m0
    for j = 1:n0
        avr_HL = avr_HL + HL(i,j);
    end
end
avr_HL = avr_HL / (m0*n0);

%判断嵌入的子带
if avr_LH <= avr_HL
    num = 0; loca = LH;
else
    num = 1; loca = HL;
end
%%
%提取水印
if num == 0
    rw = wm_extr_type1(loca);  %写出提取子函数
else
    rw = wm_extr_type0(loca);  %写出提取子函数
end


function rw = wm_extr_type1(loca)

[mm,nn] = size(loca);
index = 1;
%取出2*2的块
for k = 1:2:mm-1
    for kk = 1:2:nn-1
        tem = loca(k:k+1,kk:kk+1);
        a11 = tem(1,1);
        a12 = tem(1,2);
        a21 = tem(2,1);
        a22 = tem(2,2);
        %-------a11+a21 >= a12+a22则水印为0，否则为1-------
        if a11 + a21 >= a12 + a22
            rw(index) = 0;
        else
            rw(index) = 1;
        end
        index = index + 1;
    end
end

function rw = wm_extr_type0(loca)

[mm,nn] = size(loca);
index = 1;
%取出2*2的块
for k = 1:2:mm-1
    for kk = 1:2:nn-1
        tem = loca(k:k+1,kk:kk+1);
        a11 = tem(1,1);
        a12 = tem(1,2);
        a21 = tem(2,1);
        a22 = tem(2,2);
        %-------a12+a22 >= a11+a21则水印为0，否则为1-------
        if a12 + a22 >= a11 + a21
            rw(index) = 0;
        else
            rw(index) = 1;
        end
        index = index + 1;
    end
end