Image Processing

The area of interest of this project is Image Processing. In this project the data of an image is used in another image as some sort of digital signature in order to prevent anyone else from stealing the information.
' 1.2 Motivation:
The motivation of this project is the fact that in this digital world , everything is done based on the internet that include sending and receiving data which could be private to the user and they would not want someone seeing it , this could be done by safeguarding the data using this project.
' 1.3 Objective:
The objective of the project is data hiding based on image processing. In this one image is hidden behind another image in such a way that there is no visual evidence of it, yet when checked it shows the watermark.
' 1.4 Outline of report:
The report contains the literature review of the project followed by the basic work done on the project and its implementation and results, explanation of the block diagram , problems faced during this project , its advantages and applications and the references used.
Chapter 2: Literature Survey
The project, entitled 'Digital image watermarking using MATLAB' is depends on ' data hiding using lsb watermarking' technique and brief introduction toward the techniques and its literature are as under.
2.1 Literature review
The brief literature survey for 'Digital image watermarking using MATLAB' is as under
With every passing day more and more information is transmitted and received in the digital format and its growth seems to be only increasing at an exponential rate and the chance s of its use decreasing is a very mild one. Due to this ever increasing use its easy for a perpetrator to make its copy or pirate it.
There are many types of info and data like digital image , digital audio and digital video but I will be focusing on digital images in this project.
A pattern of bits inserted into an image of any sort in order to mark it so that it could be identified for copyright protection so that the rights of the authors can be protected is called a watermark. It is derived from the very faint visible marks on an image.
Unlike printed watermarks which are slightly visible, digital watermarks are made in such a way that they are completely invisible, for that to happen the bits must be placed in such a way that it cannot be recognized.

Digital Watermarking works by concealing information within digital data, such that it cannot be detected without knowing the way it was encrypted in the first place.
Chapter 3: 'Digital image watermarking using MATLAB'
3.1 Introduction
Content protection measure for the prevention of copyright violations from unauthorized user is the new challenge in large scale content distribution environments. Watermarking is solution for this problem.
Data is becoming easily available using internet. These connected networks allow cross-references between databases. Now multimedia is allowing different applications to mix sound, images, and video and to interact with large amounts of information.The job is to deliver audio, image and video data in electronic form to customers, and broadcast television companies and major corporations are converting their content from analog to digital form. This movement from traditional content, such as paper documents, analogue recordings, to digital media is due to several advantages of digital media over the traditional media.
Digital Watermarking Techniques are becoming popular, especially for adding undetectable identifying marks, such as author or copyright information. Because of this use, watermarking techniques are often evaluated based on their invisibility, recoverability, and robustness. Our goal was to implement watermarking method and evaluate their susceptibility to attack by various image processing techniques.
3.2 Technical Details
The purpose of digital watermarks is to provide copyright protection for information that is in digital format.
In the coming pages we will see, Alice creates an original image and watermarks it before passing it to Bob. If Bob steals the image and sells copies to other people Alice can extract her watermark from the image proving her copyright to it.
The catch here is that Alice will only be able to prove her copyright of the image if Bob hasn't managed to modify the image such that the watermark is damaged enough to be undetectable or added his own watermark such that it is impossible to discover which watermark was embedded first.
3.3 Description
Digital watermarking technology makes use of the fact that the human eye has only a limited ability to observe differences. If there are only little changes in such a way that they are barely discernible by the naked eyes such as minor modifications in the colour values of an image are subconsciously corrected by the eye, so that the observer does not notice any difference.
A secret key (string or integer) produces a random number which determines the particular pixels, which will be protected by the watermarking. The watermark is embedded redundantly over the whole image, so that every part of the image is protected. This particular type of watermarking is executed in this project.
One way of doing this is by 'Patchwork'. This technique uses a random number generator to select n pairs of pixels and slightly increases or decrease their luminosity (brightness level). Thus the contrast of this set is increased without any change in the average luminosity of the image. With suitable parameters, Patchwork even survives compression using JPEG.
Although the amount of secret information has no direct impact on the visual fidelity of the image or the robustness of the watermark, it plays an important role in the security of the system. The key space, that is the range of all possible values of the secret information, x must be large enough to make exhaustive search attacks impossible.
In the process of extracting the watermark, the secret key is used to identify the manipulated pixels and finally to decode the watermark.
Another way is defining the number of pixels in which the watermark image pixels are added to the base image without showing any discernible difference among the two.
The quality of digital watermarks can be judged in two ways; firstly it must be able to resist intentional and unintentional attacks and secondly the embedded watermark must not detract from the quality of the image.
The higher the resistance of a watermark against attacks, the higher the risk of the quality of the image being reduced, and the greater the chance of obvious visual artefacts being created.
3.4 Methods used to test watrmark robustness
These are some of the methods that can be used to test whether a watermark can survive different changes to the image it is embedded in.
3.4.1 Horizontal flipping
Many images can be flipped horizontally but we have to make sure the basic constitution of he image does not get affected due to this and the image is resilient enough to survive the change.
3.4.2 Rotation/Cropping

One other way is to rotate the image by a certain degree and then align inti it a cropped watermark which makes it very hard to detect.
3.4.3 JPEG Compression/Re-compression
JPEG is a widely used compression algorithms for images and any watermarking system should be resilient to some degree to compression or change of compression level e.g. from 71% to 70% in quality . We too have used the JPEG compression technique n his very project.
3.4.4 Scaling
Another method used for robustness is scaling, we can scale the image at twice its size or half its size in both horizontal and vertical direction.Uniform scaling increases/decreases an image by the same rate in the horizontal and vertical directions. Non-uniform scaling increases/decreases the image horizontally and vertically at different rates. Digital watermarking methods are often resilient only to uniform scaling.
3.5 Technique used
There can be two type of watermarking
(a) Invisible Watermarking
(b) Visible Watermarking
The technique I have used in this project is called Least Significant Bit Watermarking or in short the LSB method.
It is an invisible watermarking technique that changes the LSB's of the original image by the MSB's of the watermark image.
3.6 Working Concept
1. A bitmap image 'A' will be selected from the set of standard test images. Let this be the base image on which the watermark will be added.
2. A bitmap image 'B' will be selected from the set of standard test images. This will be the watermark image which will be added to the base image.
3. The most significant bit henceforth will be mentioned as MSB, of watermark image 'B' will be read and these will be written on the least significant bit, henceforth will be mentioned as LSB, of base image 'A'.
4. Thus, 'A' will be watermarked with 'B' resulting in a combined image 'C'.
5. 'C' therefore will now contain an image 'A' which has its LSBs replaced with the MSBs of 'B'.
6. The technique used will be LSB technique which is a form of spatial domain technique.
7. This technique is used to add an invisible and visible watermark in the image.
3.7 Generated Code
base_image = input('Enter base image file name with extension : ', 's');
watermark_image = input('Enter watermark image file name with extension: ', 's');
base = imread(base_image);
watermark = imread(watermark_image);
figure(1) Digital Watermarking 27 Abrar Ahmed Syed 1000614216
imshow(base,[])
title('Original Image (Cover Image/Base Image)')
figure(2)
imshow(watermark,[])
title('Watermark Image (Image which will hide in cover image)')
base=double(base);
watermark=double(watermark);
bits=1;
watermark_shifted=bitshift(watermark,-(8-bits));
for i=1:bits
base=bitset(base,i,0);
end
watermarked_image = uint8(base+watermark_shifted);
figure(3)
imshow(watermarked_image,[])
title('Watermarked Image (Final watermarked image)')
imwrite(watermarked_image,'invsible watermarked image.bmp');
3.8 Visible Watermarking
By changing the numberof bits we can change the type of watermarking from invisible to visible.
By changing the number of bits from 3 to 5 we can do the aforementioned.
3.9 Noise addition to the watermarked image
imdata = imread('Visible Watermarked.bmp');
noisy = rand([512 512]);
imdata1= double(imdata) + double(noisy);
imdata1 = uint8(imdata1);
figure(4)
imshow(imdata1,[])
title('Watermarked image with noise added to it')
imwrite(imdata1,'Noisy.bmp')
3.10 JPEG compression of the image
Chapter 4: Implementations and Result
4.1 Block Diagram
4.2 Explanation
An exact number of these bits will be made zero in the LSB of the base image. The reason for making
them zero, is to provide space for the MSB of watermark to be stored.
The bits of both the images, i.e. watermark image which now has its MSB shifted to its LSB, and the base
image, which has its LSBs are set zero, are added. The added image gives us the watermarked signal.
The final image obtained.
4.3 Designing Steps
The designing is based on software and the software which is used in this case is MATLAB.
The aim of the program is to replace the LSB of the base image with the MSB of the watermark. First, the generated code will ask the user for the images to be used as base image and watermark image.
The user will then enter the name of the images, both the base and the watermark, with their extension.
Both these images will be read and stored by the tool, which is 'Matlab' in our case.
MATLAB will also display these images to the user with their respective titles in different figures.
The program will then change the image size to double. This is done so as to tell the software that we need to give double data-type space for the images. The reason for doing so, is to provide decimal storage for the subsequent additional operations which will be performed on the base and watermark image.
The next step is to give the number of MSB's of the watermark image which will be used to exchange the LSB's of the base image. Once we provides this, the watermark signal bits are shifted to the right by the specified bits.
The next step is the number of LSB's of the base image are made zero to accept the bits of the watermark image.
These two images with the defined bit pattern are added.
The combined image we get will be 5 bits of the base image and the last 3 bits are the watermark image and it will be the output watermarked image.
4.3 Results
The result of the aforementioned processes are shown below:
(a)Base image
(b)Watermark image
(c)Watermarked image using invisible watermarking technique
(d)Watermarked image with visual watermarking
(e)Visible watermarking with noise added to it
(f)JPEG compressed watermarked image

4.4 Problems faced
The problem faced by me was that when the image sizes were very different its hard to get visible watermarking even after substituting more than 3 bits.
Another problem was the dimensions of the two images , both the images must have the same dimensions in order for the program to work. To overcome that i cropped the image to make both the images of the same dimensions so that they can be added easily.
Chapter 5: Conclusion
5.1 Conclusion:
Thus, using Matlab, two forms of watermarking techniques are implemented. One being invisible and the other being visible. Noise is added to the images as a form of attack. The images are compressed and decompressed as another form of attack. The noise is later removed and the base and watermark images are separated from the watermarked image.
5.2 Future work :
In future i am planning to work on watermarking using DCT and DFT and IDFT.
Chapter 6 : References
[1]G. K. Wallace, 'The JPEG still picture compression standard', IEEE Trans. on Consumer Electronics, Vol. 38, pp.18-34, Feb. 1992.
[2]R. Popa, 'An analysis of steganographic techniques', The Politehnica University of Timisoara, Faculty of Automatics and Computers, Department of Computer Science and Software Engineering
[3] P. Vidyasagar, S. Han and E. Chang. "A survey of digital image watermarking techniques', 3rd IEEE International Conference on Industrial Informatics (INDIN 2005), edited by T. Dillon, X. Yu. and E. Chang, pp. 495-502, Perth, Western Australia, 2005.
[4] J. Dugelay and S. Roche, 'A Survey of Current Watermarking Techniques' in Information Techniques for Steganography and Digital Watermarking, S.C. Katzenbeisser et al, Eds. Northwood, MA: Artec House, pp. 121-145, Dec. 1999.
[5] I. J. Cox, et al, "Digital watermarking and steganography" (Second Edition), Morgan Kaufmann, 2008.
[6] Digital image watermarking by Abrar Ahmed Syed.
[7] A. Khan and A.M. Mirza, 'Genetic perceptual shaping: utilizing cover image and conceivable attack information during watermark embedding'. Inf. Fusion, Vol. 8, pp. 354-365, Oct. 2007.
[8] Digital Watermarking 4th International Workshop, IWDW 2005, Siena, Italy
[9] Digital Image Watermarking - Research Papers
[10] Document and Image Compression - Google Books34
[11] I.J. Cox, M.L. Miller, J.M.G. Linnartz and T. Kalker, 'A Review of Watermarking Principles and Practices' in Digital Signal Processing for Multimedia Systems, K.K. Parhi and T. Nishitani, New York, Marcel Dekker, New York, pp. 461-482, 1999.

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