HIDE THE SIX TEXT PAGES IN A COLOR IMAGE
Contents
About me:
- A.Cherma Rajan,(2003-2007 Batch),
- BE.,Electronics & Communication Engineering,
- Kamaraj college of Engineering and Technology,
- Madurai-1,
- India.
- E-mail:chermarajan@yahoo.co.in
About this Program:
This program can encode the text images (6 images max) in a single color image. And also can easily recover the texts already
being hided. It is very simple one,but very useful Major advantage of this encoded image is like a original image as before
encoding. The image has no visible changes. So no one can easily read the hidden texts by sight. The decoding logic only can
recover the texts. Thus this special features of encoded image make it used to save the confidential data. Also can used for
web applications, mail services, media etc.,. Can we avoid any one can read/modify our own data.
Tips to use my program:
- For better results images should be in 24-Bit bit map(bmp) format.
- Use larger size image (> 512 X 512)
- Avoid small size Fonts.
- All images should be in the same size.
- Text data should be converted to image format (bmp) before execution.
- Text data should be monochrome(Black letters) ,color text leads to undesire results.
- Change the address of the image mentioned in this program as per your location in Local drive.
- No need to specify the dimension of the image.
Part One: Initialize the Input
In this part obtained the input (1 Color image + 6 Text images) from local drive. Collect all images as a separate variable.
Change the location of the image mentioned in imread() function as per your image.
clc;
close all;
clear all;
im=imread('d:\Documents and Settings\Cherma\Desktop\new\123.bmp');
tx1=imread('d:\Documents and Settings\Cherma\Desktop\new\1.bmp');
tx2=imread('d:\Documents and Settings\Cherma\Desktop\new\2.bmp');
tx3=imread('d:\Documents and Settings\Cherma\Desktop\new\3.bmp');
tx4=imread('d:\Documents and Settings\Cherma\Desktop\new\4.bmp');
tx5=imread('d:\Documents and Settings\Cherma\Desktop\new\5.bmp');
tx6=imread('d:\Documents and Settings\Cherma\Desktop\new\6.bmp');
figure(1);
subplot(2,3,1);imshow(tx1);title({'Text to be Encoded';'Page 1'});
subplot(2,3,2);imshow(tx2);title('Page 2');
subplot(2,3,3);imshow(tx3);title('Page 3');
subplot(2,3,4);imshow(tx4);title('Page 4');
subplot(2,3,5);imshow(tx5);title('Page 5');
subplot(2,3,6);imshow(tx6);title('Page 6');
Part Two: Image Encoding
In this part the desire text images (max 6 images) are going to encoded with the Color image. At first pair of text images
are combined into a single image. Simple logic is used to achieve this. Pixels are selected from alternate location of pair
of text images. As a result of this, image having details (but alternate locations) about pair of two text images. Further
explained that if a location (n,m) have the pixel of Image 1 next location (n+1,m+1) have the pixel taken from Image 2. This
task is done by alterim() function. Two arguments of this function are two text images.
Next step is to encode the text image which was already obtained from the result of alterim() function. We obtained 3 single
text images from this function. Each image is encoded in each color frames R,G and B respectively. To do this I used a simple
logic. i.e. encode the text image as a bit of color image LSB. Because LSB bit is very less significant, so changing this
bit won't affect the entire image. Further the text image is having only black and white area. So I fix a threshold as 128.
If a pixel value of a text image is >128, LSB of Color image is set as '1' otherwise '0'. Simply says if text is present set
that LSB as 1 otherwise 0. Similar way I do it for other two color frames. All the above operations are performed by imhide()
function for each frame respectively. Arguments of this function are a color frame and a text image obtained from alterim()
function. Finally each frames are added to form a Encoded Water mark image.
NOTE: In bmp format each color frame bits are represented by 8-bits. We took the LSB of that 8-bit.
tx1=alterim(tx1,tx2);
tx2=alterim(tx3,tx4);
tx3=alterim(tx5,tx6);
R(:,:,1)=imhide(im(:,:,1),tx1); R(:,:,2:3)=0;
G(:,:,2)=imhide(im(:,:,2),tx2); G(:,:,1:2:3)=0;
B(:,:,3)=imhide(im(:,:,3),tx3); B(:,:,1:2)=0;
temp=R+G+B;
figure(2);subplot(1,2,1);
imshow(im);
title({'Color image';'(Before Encoding)'});
figure(2);subplot(1,2,2);
imshow(uint8(temp));
title({'Watermarked image';'(After Encoding)'});
Part Three: Recovery of Text image
In this part two functions are used to recover the text image from Encoded image. First step is to extract the text image.
Remember that text image encoded in the color image in each frame is the alternate combination of two images (Text). The function
txtxtract() just extract the text image which is the combination of two text images, not by separate. As we encode our data
in LSB of each color frame that bit alone sufficient to reconstruct our text image. So logical AND operation is used to recover
the LSB. Reverse operation of function imhide() is used to reconstruct the text. Next step is to separate the pair of two
text images from the result of function txtxtract(). Alternate selection used in previous Encoding section is used again for
all pair of images.
R=txtxtract(temp(:,:,1));
G=txtxtract(temp(:,:,2));
B=txtxtract(temp(:,:,3));
[tx1 tx2]=imxtract(R);
[tx3 tx4]=imxtract(G);
[tx5 tx6]=imxtract(B);
Part Four: Edge tappering
This part is the final step in my program. The images obtained from previous step is not a tappered. So finally all text images
are smoothen by using fspecial() function available in MATLAB.
PSF = fspecial('laplacian');
figure(3);
subplot(2,3,1);imshow(medfilt2(edgetaper(tx1,PSF)));title({'Extracted Text';'Page 1'});
subplot(2,3,2);imshow(medfilt2(edgetaper(tx2,PSF)));title('Page 2');
subplot(2,3,3);imshow(medfilt2(edgetaper(tx3,PSF)));title('Page 3');
subplot(2,3,4);imshow(medfilt2(edgetaper(tx4,PSF)));title('Page 4');
subplot(2,3,5);imshow(medfilt2(edgetaper(tx5,PSF)));title('Page 5');
subplot(2,3,6);imshow(medfilt2(edgetaper(tx6,PSF)));title('Page 6');
