function QQ=dct_det(attacked,tao)
Q_table=[16 11 10 16 24 40 51 61;
        12 12 14 19 26 58 60 55;
        14 13 16 24 40 57 69 56;
        14 17 22 29 51 87 80 62;
        18 22 37 56 68 109 103 77;
        24 35 55 64 81 104 113 92;
        49 64 78 87 103 121 120 101;
        72 92 95 98 112 100 103 99
        ];

ZT=attacked;
[m n]=size(ZT);
chuangai=zeros(m,n);
chuangai=attacked;

quality=50;
%塊dct變換
for i=1:(m/8);
    for j=1:(n/8);
        width=(i-1)*8+1;
        height=(j-1)*8+1;
        imdct(width:(width+7),height:(height+7))=dct2(ZT(width:(width+7),height:(height+7)));
    end
end
%開辟要比較的數據空間
Q=zeros(1,m*n/8/8/2*6);
watermark=zeros(1,m*n/8/8*6);
%比較zig-zag前6個對應系數
wm_cof=[1 1;2 1;1 2;1 3;2 2;3 1];

k=1;
for i=1:(m/8/2);
    for j=1:(n/8);
          width=(i-1)*16;
        height=(j-1)*8;
        l=(k-1)*6+1;
        for ppp=1:6
%   if round((imdct(width+wm_cof(ppp,1),height+wm_cof(ppp,2))-imdct(width+wm_cof(ppp,1)+8,height+wm_cof(ppp,2)))/(Q_table(wm_cof(ppp,1),wm_cof(ppp,2))+1))<tao
   if round((imdct(width+wm_cof(ppp,1),height+wm_cof(ppp,2))-imdct(width+wm_cof(ppp,1)+8,height+wm_cof(ppp,2)))/(Q_table(wm_cof(ppp,1),wm_cof(ppp,2))))<tao

        %     if round(imdct(width+wm_cof(ppp,1),height+wm_cof(ppp,2)))-round(imdct(width+wm_cof(ppp,1)+8,height+wm_cof(ppp,2)))<tao
  
            Q(l+ppp)=0;
        else
            Q(l+ppp)=1;
        end
        end
         k=k+1;
    end
end
% imwrite(uint8(J2),'lena256.jpg','quality',quality);
% yy=imread('lena256.jpg');

em_cof=[1 4;2 3;3 2;4 1;4 2;3 3];
%em_cof=[4 4;4 5;5 4;2 6;6 2;3 5];
NN=size(em_cof,1);
    
k=1;
err=0;
for i=1:(m/8/2)
    for j=1:(n/8)
        width=(i-1)*16;
        height=(j-1)*8;
        l=(k-1)*6+1;
     err_block=0;
         for kk=1:3  
         qstep=Q_table(em_cof(kk,1),em_cof(kk,2))+1;
           watermark(l)=mod(round(imdct(width+em_cof(kk,1),height+em_cof(kk,2))/qstep),2);
       if watermark(l)~=Q(l)
         
           err_block=err_block+1;
     %  chuangai((width+1):(width+16),(height+1):(height+8))=1;                
       end
        l=l+1;
         end
         
       width=(i-1)*16+8;
       height=(j-1)*8;
       for kk=4:NN  
       qstep=Q_table(em_cof(kk,1),em_cof(kk,2))+1;
          watermark(l)=mod(round(imdct(width+em_cof(kk,1),height+em_cof(kk,2))/qstep),2);
       if watermark(l)~=Q(l)
        
              err_block=err_block+1;
    %  chuangai((width+1):(width+16),(height+1):(height+8))=1;                       
       end
       l=l+1;
       
       end
         
            if err_block>1
                   err=err+1;
            chuangai((width-7):(width+8),(height+1):(height+8))=0; 
             end
         k=k+1;
   end
end

figure(2);
imshow(uint8(chuangai));
imwrite(uint8(chuangai),'cuangai.bmp','bmp');
QQ=Q;
err