%將水印圖像按最不重要位(LSB)方法嵌入到載體圖像中，在把水印從載體圖像中提取出來
%注:整個算法分為水印嵌入部分和水印提取部分。
function [cover_object,message,watermarked_image,watermark]= lsb(file_name,water_name) 

% 讀入載體圖像
cover_object=imread(file_name);
imshow(cover_object,[])
% 讀入水印圖像
message=imread(water_name);
imshow(message,[])
message=double(message);
message=round(message./256);
message=uint8(message);
% 確定載體圖像的大小
Mc=size(cover_object,1);
Nc=size(cover_object,2);
% 確定水印圖像的大小
Mm=size(message,1);
Nm=size(message,2);
for ii = 1:Mc
    for jj = 1:Nc
        watermark(ii,jj)=message(mod(ii, Mm)+1,mod(jj, Nm)+1);
    end
end
watermarked_image=cover_object;
for ii = 1:Mc
   for jj = 2:Nc
       watermarked_image(ii, jj)=bitset(watermarked_image(ii, jj), 1, watermark(ii ,jj));
   end 
end
imwrite(watermarked_image,'lsb_watermarked.bmp','bmp');
% 計算已嵌入水印圖像的PSNR
%psnr=PSNR(cover_object, watermarked_image),
% 顯示已嵌入水印的圖像 e
imshow(watermarked_image,[])
file_name='lsb_watermarked.bmp';
watermarked_image=imread(file_name);
Mw =size(watermarked_image,1);
Nw =size(watermarked_image,2);
for ii = 1:Mw
   for jj = 1:Nw
       watermark(ii, jj)=bitget(watermarked_image(ii, jj),1);
   end
end
watermark=256*double(watermark);
%顯示提取的水印圖像
imshow(watermark,[])