lsb_test.asv

在bmp图像中隐藏另一图像

function LSB_test
%LSB_test is the LSB althorithm for picture

function S=PSNR(Im_original,Im_modified)
%Define for PSNR

if(size(Im_original)~=size(Im_modified))
    error('错误：两个输入图像大小不一致！')
end
if(~isrgb(Im_original)&~isrgb(Im_modified))
    [m n]=size(Im_original);
    A=double(Im_original);
    B=double(Im_modified);
    sumaDif=0;
    maxI=m*n*max(max(A.^2));
    for u=1:m
        for v=1:n
            sumaDif=sumaDif+(A(u,v)-B(u,v))^2;
        end
    end
    if (sumaDif==0)
        sumaDif=1;
    end
    S=maxI/sumaDif;
    S=10*log10(S);
else
    error('错误：输入图像为彩色图像')
end

%.............................LSB水印嵌入算法....................................
clear all;
%读入载体图像
file_name='lena.bmp';
cover_object=imread(file_name);
%读入水印图像
file_name='copyright.bmp';
message=imread(file_name);
message=double(message);
message=round(message./256);
message=uint8(message);
%确定图像的大小
Mc=size(cover_object,1);
Nc=size(cover_object,2);
%确定水印图像的大小
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=1:Nc
        watermarked_image(ii,jj)=bitset(watermarked_image(ii,jj),1,watermark(ii,jj));
    end
end
imwrite(watermarked_image,'lsb_watermarked.bmp','bmp');
%计算已嵌入水印图像的PSNR
psnr=PSNR(cover_object,watermarked_image);
%显示已嵌入水印的图像e
figure(1);
%subplot(2,2,1);
imshow(watermarked_image,[]);
title('Watermark Image');

%.............................LSB水印提取算法....................................
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);
%显示提取的水印图像
figure(2);
%subplot(2,2,2)
imshow(watermark,[]);
title('Recovered Watermark')