MATLAB Answers

Aseel H
0

LSB code

Asked by Aseel H
on 26 Nov 2011
Latest activity Commented on by Walter Roberson
on 10 Sep 2016

I want hide a text in image using LSB algorithm

for example:

X = image;
S = secret message;

I write:

X2(:)=bitset(X(:),1,S(:));

but when run i have an error

"??? Error using ==> bitset
Inputs must be non-negative integers."

after convert to binary i have another error

??? Undefined function or method 'bitset' for input arguments of type 'char'.

please help me.

  1 Comment

Michael Chan
on 21 Apr 2012

Similar methods are used in Matlab in the following example for static images:

http://www.mathworks.com/matlabcentral/fileexchange/36288-embedding-hiding-image-within-image-with-n-bit-lsb-steganography

http://www.mathworks.com/matlabcentral/fileexchange/36275-image-description-notes-with-n-bit-lsb-steganography

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4 Answers

Image Analyst
Answer by Image Analyst
on 27 Nov 2011
 Accepted answer

Well here's my demo. It lets you hide an watermark image, which may be bigger or smaller than a cover image, into a user-specified bitplane of the cover (original) image. If the watermark is bigger than the original image, it scales it down. If the watermark is smaller, it tiles it. The watermark image can be grayscale and you can specify where you want it thresholded at. It uses standard MATLAB demo images. If the images are color, it takes the red channel - I haven't made it to work with color images. At the end it adds noise and recovers the watermark from the noise-free and noisy images, so you can see how lousy this method is as far as being robust to attack.

% Demo to watermark an image by hiding another image in a certain bit
% plane.  Sometimes called "LSB Watermarking" or something similar.
% User is asked which bit plane they want to hide the image in.
% By Image Analyst.
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
imtool close all;  % Close all imtool figures.
clear;  % Erase all existing variables.
workspace;  % Make sure the workspace panel is showing.
fontSize = 12;
% Read in the image what will have another image hidden into it.
baseFileName='moon.tif';
% baseFileName='cameraman.tif';
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
if ~exist(fullFileName, 'file')
	% Didn't find it there.  Check the search path for it.
	fullFileName = baseFileName; % No path this time.
	if ~exist(fullFileName, 'file')
		% Still didn't find it.  Alert user.
		errorMessage = sprintf('Error: %s does not exist.', fullFileName);
		uiwait(warndlg(errorMessage));
		return;
	end
end
originalImage = imread(fullFileName);
% Get the number of rows and columns in the original image.
[visibleRows visibleColumns numberOfColorChannels] = size(originalImage);
if numberOfColorChannels > 1
	% If it's color, extract the red channel.
	originalImage = originalImage(:,:,1);
end
% Display the original gray scale image.
subplot(3, 3, 4);
imshow(originalImage, []);
title('Original Grayscale Starting Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
set(gcf,'name','Demo by ImageAnalyst','numbertitle','off') 
% read the message image you want to hide in the cover image
baseFileName='cameraman.tif';
% baseFileName='moon.tif';
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
if ~exist(fullFileName, 'file')
	% Didn't find it there.  Check the search path for it.
	fullFileName = baseFileName; % No path this time.
	if ~exist(fullFileName, 'file')
		% Still didn't find it.  Alert user.
		errorMessage = sprintf('Error: %s does not exist.', fullFileName);
		uiwait(warndlg(errorMessage));
		return;
	end
end
hiddenImage = imread(fullFileName);
% Get the number of rows and columns in the hidden image.
[hiddenRows hiddenColumns numberOfColorChannels] = size(hiddenImage);
if numberOfColorChannels > 1
	% If it's color, extract the red channel.
	hiddenImage = hiddenImage(:,:,1);
end
% Display the image.
subplot(3, 3, 1);
imshow(hiddenImage, []);
title('Image to be Hidden', 'FontSize', fontSize);
% Let's compute and display the histogram.
[pixelCount grayLevels] = imhist(hiddenImage);
subplot(3, 3, 2); 
bar(pixelCount);
title('Histogram of image to be hidden', 'FontSize', fontSize);
xlim([0 grayLevels(end)]); % Scale x axis manually.
grid on;
thresholdValue = 70;
binaryImage = hiddenImage < thresholdValue;
% Display the image.
subplot(3, 3, 3);
imshow(binaryImage, []);
caption = sprintf('Hidden Image Thresholded at %d', thresholdValue);
title(caption, 'FontSize', fontSize);
% Get the bit plane to hide the image in.
prompt = 'Enter the bit plane you want to hide the image in (1 - 8) ';
dialogTitle = 'Enter Bit Plane to Replace';
numberOfLines = 1;
defaultResponse = {'1'};
bitToSet = str2double(cell2mat(inputdlg(prompt, dialogTitle, numberOfLines, defaultResponse)));
% If image to be hidden is bigger than the original image, scale it down.
if hiddenRows > visibleRows || hiddenColumns > visibleColumns
	amountToShrink = min([visibleRows / hiddenRows, visibleColumns / hiddenColumns]);
	binaryImage = imresize(binaryImage, amountToShrink);
	% Need to update the number of rows and columns.
	[hiddenRows hiddenColumns] = size(binaryImage);
end
% Tile the hiddenImage, if it's smaller, so that it will cover the original image.
if hiddenRows < visibleRows || hiddenColumns < visibleColumns
	watermark = zeros(size(originalImage), 'uint8');
	for column = 1:visibleColumns
		for row = 1:visibleRows
			watermark(row, column) = binaryImage(mod(row,hiddenRows)+1, mod(column,hiddenColumns)+1);
		end
	end
	% Crop it to the same size as the original image.
	watermark = watermark(1:visibleRows, 1:visibleColumns);
else
	% Watermark is the same size as the original image.
	watermark = binaryImage;
end
% Display the thresholded binary image - the watermark alone.
subplot(3, 3, 5);
imshow(watermark, []);
caption = sprintf('Hidden Image\nto be Inserted into Bit Plane %d', bitToSet);
title(caption, 'FontSize', fontSize);
% Set the bit of originalImage(a copy, actually) to the value of the watermark.
watermarkedImage=originalImage;
for column = 1:visibleColumns
	for row = 1:visibleRows
		watermarkedImage(row, column)=bitset(originalImage(row, column), bitToSet, watermark(row, column));
	end
end
% Display the image.
subplot(3, 3, 6);
imshow(watermarkedImage, []);
caption = sprintf('Final Watermarked Image\nwithout added Noise');
title(caption, 'FontSize', fontSize);
% add noise to watermarked image
noisyWatermarkedImage = imnoise(watermarkedImage,'gaussian');
% Display the image.
subplot(3, 3, 7);
imshow(noisyWatermarkedImage, []);
caption = sprintf('Watermarked Image\nwith added Noise');
title(caption, 'FontSize', fontSize);
%====================================================================================
% Now let's pretend we are starting with the watermarked noisy corrupted image.
% We want to recover the watermark.
% Use the known bitplane of watermarked image to recover the watermark.
recoveredWatermark = zeros(size(noisyWatermarkedImage));
recoveredNoisyWatermark = zeros(size(noisyWatermarkedImage));
for column = 1:visibleColumns
	for row = 1:visibleRows
		recoveredWatermark(row, column) = bitget(watermarkedImage(row, column), bitToSet);
		recoveredNoisyWatermark(row, column) = bitget(noisyWatermarkedImage(row, column), bitToSet);
	end
end
% Scale the recovered watermark to 0=255
recoveredWatermark = uint8(255 * recoveredWatermark);
recoveredNoisyWatermark = uint8(255 * recoveredNoisyWatermark);
% Display the images.
subplot(3, 3, 8);
imshow(recoveredWatermark, []);
caption = sprintf('Watermark Recovered\nfrom Bit Plane %d of\nNoise-Free Watermarked Image', bitToSet);
title(caption, 'FontSize', fontSize);
% Display the images.
subplot(3, 3, 9);
imshow(recoveredNoisyWatermark, []);
caption = sprintf('Watermark Recovered\nfrom Bit Plane %d of\nNoisy Watermarked Image', bitToSet);
title(caption, 'FontSize', fontSize);
msgbox('Done with demo!');

  4 Comments

Image Analyst
on 27 Nov 2011

No problem. Perhaps it will help someone who wants to hide an image in another image. Use Chandra's code below if you want to hide text in an image.

rasma khan
on 8 Mar 2014

Thank u so much for the help!

What is Chandra's code??


Walter Roberson
Answer by Walter Roberson
on 26 Nov 2011

What data types are X and S? That is, what does class() report for each of them?

Your S must be a vector of values, each 0 or 1. It cannot be '0' or '1', and it cannot be (e.g) 72 (which corresponds to the coding for 'H')

  1 Comment

Aseel H
on 27 Nov 2011

X is a variable to identify the image
S is a variable to identify the text that i want hide it in image
please if you have code hide text in image using LSB algorithm send me
thanks


Answer by pratiksha patil on 4 Mar 2012

But how can I again extract the original message file???????

  4 Comments

Michael Chan
on 21 Apr 2012

Similar methods are used in Matlab in the following example for static images:

http://www.mathworks.com/matlabcentral/fileexchange/36288-embedding-hiding-image-within-image-with-n-bit-lsb-steganography

http://www.mathworks.com/matlabcentral/fileexchange/36275-image-description-notes-with-n-bit-lsb-steganography

When I run this code it gives an error in below line bin_vector(idk) = bitget(cover(row,col), 7);

Error - The variable bin_vector appears to change size on every loop iteration (within script). Consider perallocating for speed

Walter Roberson
on 10 Sep 2016

That would not be an error, it would be a warning given by the editor. It is a matter of efficiency, not a matter of being incorrect MATLAB. If you want to avoid the warning you can use

    bin = zeros(cl, 8);

before the "for x = 1 : cl" loop.


sha
Answer by sha
on 21 Mar 2012

This is my example of extraction..

hopefully you can try..

%determined the size of watermarked image
mw=size(image1,1); %heigth of the watermarked image
nw=size(image1,2); %width of the watermarked image
for ii = 1: mw
      for jj = 1 : nw
          watermark (ii,jj) = bitget(image1(ii,jj),1);
      end
  end    
figure(2)
imshow(watermark);  
title('extracted image');     % watermark image for watermarking 

  1 Comment

ghassan78
on 27 Jan 2014

ok my bro , but i think this code don't work with color watermark ... just with gray


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