隐写术基于DCT系数

Question

我正在尝试使用LSB进行隐写术，但我得到了大量黑色像素的图像    iam替换DCT值小于零的覆盖图像像素中的LSB    我不知道为什么我的图像中有黑色像素

 % read cover  image
 C=imread('E:\sofia1.jpg');   

 % read Secret image       
 S=imread('E:\mandrill.jpg');  

 C=C(:,:,1);

 S=S(:,:,1);
 [r1 c1]=size(C);
  CDCT=dct2(C); 
  CDCTR= real(CDCT); 
  for i=1:r1 
for j=1:c1 
    %CDCTR(i,j)
   if(CDCTR(i,j)<0)
      b=bitget(S(i,j),8);
      %disp(b)
      x=bitset(C(i,j),1,b);  % replace LSB in cover image with MSB in 
      C(i,j)=x;

      TM(i,j)=1;    % put 1 in the trace mmatrix when successful repalce  
   else
      TM(i,j)=0;     % put 0  in the trace matrix when no replace 
   end   

   end    
 end
  %Retreive again the Secret image from the covered image 
  n=1;
  for i=1: r1 
     for j=1:c1 
       if(TM(i,j)==1)      
        b=bitget(C(i,j),1); 
        E(i,j)=b; %bitset(E(i,j),8,b) ;
   %else 
      %E(i,j)=; 
     end

    end   
  end

  figure(5), imshow(mat2gray(E)),title('Extracted Secret Image'),