lsb_recover.m

LSB域的恢复算法

% 最不重要位（LSB-least significant bit）方法是一种最简单的嵌入方法。任何形式的秘密信号都可以转换成一串二进制码流，而音频文件的每一个采样数据也是用二进制数来表示。这样，可以将每一个采样值的最不重要位（多数情况下为最低位），用代表秘密信息的二进制位替换，以达到在音频信号中嵌入秘密信息的目的。为了加大攻击的难度，可以使用一段伪随机序列来控制秘密信息嵌入的位置。

%Name:		Chris Shoemaker
%Course:	EER-280 - Digital Watermarking
%Project: 	Least Significant Bit Substitution 
%           Watermark Recovery

clear all;

% save start time
start_time=cputime;

% read in watermarked image
file_name='lsb_watermarked.bmp';
%file_name='_lena_std_bw.bmp';
watermarked_image=imread(file_name);

% determine size of watermarked image
Mw=size(watermarked_image,1);	%Height
Nw=size(watermarked_image,2);	%Width

% use lsb of watermarked image to recover watermark
for ii = 1:Mw
    for jj = 1:Nw
        watermark(ii,jj)=bitget(watermarked_image(ii,jj),1);
    end
end

% scale the recovered watermark
watermark=2*double(watermark);

% display processing time
elapsed_time=cputime-start_time,

% read in original watermark
%file_name='_copyright_large.bmp';
%orig_watermark=imread(file_name);

% scale and display recovered watermark
figure(2)
imshow(watermark,[])
title('Recovered Watermark')