%整理自lufei的水印代码(数字水印论坛)
%整理:wyy022
%Project: Threshold-Based Correlation in DCT mid-band
% Uses two PN sequences; one for a "0" and another for a "1"
% 水印嵌入
clear all;
% 保存开始时间
start_time=cputime;
k=10; % 设置嵌入强度
blocksize=8; % 设置块的大小
midband=[ 0,0,0,1,1,1,1,0; % defines the mid-band frequencies of an 8x8 dct
0,0,1,1,1,1,0,0;
0,1,1,1,1,0,0,0;
1,1,1,1,0,0,0,0;
1,1,1,0,0,0,0,0;
1,1,0,0,0,0,0,0;
1,0,0,0,0,0,0,0;
0,0,0,0,0,0,0,0 ];
% 读入原始图像
file_name='_lena_std_bw.bmp';
cover_object=double(imread(file_name));
% 原始图像的行数与列数
Mc=size(cover_object,1); %原图的行数
Nc=size(cover_object,2); %原图的列数
% 确定可嵌入的最大信息量
max_message=Mc*Nc/(blocksize^2);
% 读入水印图像
file_name='c.bmp';
message=double(imread(file_name));
%水印图像的行数与列数
Mm=size(message,1); %水印图像的行数
Nm=size(message,2); %水印图像的列数
figure(1)
imshow(message,[]);
title('水印');
% 将水印图像矩阵转换为0,1组成的向量
message=reshape(message,1,Mm*Nm);
% 检查水印信息是否过大
if (length(message) > max_message)
error('水印太大')
end
% 将message_vector置为全1向量,并将message写入
message_vector=ones(1,max_message);
message_vector(1:length(message))=message;
% 将cover_object写入watermarked image
watermarked_image=cover_object;
key=1100;
% 重置随机数发生器状态为key
rand('state',key);
% 生成伪随机数
pn_sequence_zero=round(2*(rand(1,sum(sum(midband)))-0.5));
% 图象分块并嵌入
x=1;
y=1;
for (kk = 1:length(message_vector))
% 分块进行DCT变换
dct_block=dct2(cover_object(y:y+blocksize-1,x:x+blocksize-1));
% 如果message_vector==0 并且midband==1,那么嵌入 pn_sequence_zero
ll=1;
if (message_vector(kk)==0)
for ii=1:blocksize
for jj=1:blocksize
if (midband(jj,ii)==1)
dct_block(jj,ii)=dct_block(jj,ii)+k*pn_sequence_zero(ll);
ll=ll+1;
end
end
end
end
% 逆DCT变换
watermarked_image(y:y+blocksize-1,x:x+blocksize-1)=idct2(dct_block);
% 移动到下一块
if (x+blocksize) >= Nc
x=1;
y=y+blocksize;
else
x=x+blocksize;
end
end
% 转换为uint8 并将watermarked_image_uint8写入watermarked_image_uint8.bmp
watermarked_image_uint8=uint8(watermarked_image);
imwrite(watermarked_image_uint8,'watermarked_image_uint8.bmp','bmp');
% 显示运行时间
elapsed_time=cputime-start_time,
% 计算psnr
psnr=psnr(cover_object,watermarked_image),
% 显示嵌入水印图象与原始图象
figure(2)
subplot(1,2,1);
imshow(watermarked_image_uint8,[])
title('嵌入水印图像')
subplot(1,2,2)
imshow(cover_object,[]);
title('原始图像');
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