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Invisible_Digital_Watermarking

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Invisible_Digital_Watermarking

    ECE 6550 Project

    Invisible Digital Watermarking

    Based on DCT

    Chen, Shengfeng

    Jia, Zhuokang

    Instructor: Dr. Ikhlas Abdel-Qader, P.E.

    thJune 27 2010

    Western Michigan University

    THIS PROJECT IS INVISIBLE DIGITAL WATERMARKING DESIGN AND SIMULATION, USING MATLAB

    ECE6550 Invisible Digital Watermarking Based on DCT 1

    1. Introduction: ............................................................................................................................. 2

    2. Background ............................................................................................................................... 2

    3. Methods .................................................................................................................................... 3

    3.1 DCT transform ............................................................................................................... 3

    3.2 Watermarking Preprocessing ........................................................................................ 4

    3.3 Characteristics of Digital Image Watermarking ............................................................. 5

    3.4 Flow Diagram of Invisible Digital Watermarking ........................................................... 5

    3.5 Watermark embedding ................................................................................................. 6

    3.6 Blind Extraction of watermark ...................................................................................... 7

    3.7 Assessment index .......................................................................................................... 7

    4. Analysis and simulation of algorithm performance ................................................................ 8

    4.1 Test of performance after attacking. ........................................................................... 10

    4.1.1 JPEG compression ........................................................................................... 10

    4.1.2 Image Cropping ............................................................................................... 12

    4.1.3 Salt & Pepper Noise ......................................................................................... 14

    4.1.4 Gaussian Noise ................................................................................................ 14

    4.1.5 Gaussian low-pass Filter .................................................................................. 15

    4.2 Comparison between DC and low frequency AC component. .................................... 16 5. Conclusion .............................................................................................................................. 17

    Reference ........................................................................................................................................ 18

    Appendix ......................................................................................................................................... 19

    Matlab Code: ................................................................................................................................... 19

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    ECE6550 Invisible Digital Watermarking Based on DCT 2

    1. Introduction:

    In recent years, digital watermarking techniques have been extensively exploited and regarded as a potentially effective solution against illegal reproduction or theft of multimedia contents. Watermarking is the process that embeds information which could be data, tag or label into a multimedia object such that watermark can be detected or extracted later to make an affirmation about the object. An important classification is to divide watermarking techniques into visible and invisible according to the visibility of watermark data in embedded contents. Generally, visible watermarking schemes are used to protect digital images or videos that have to be released for certain purposes, such as contents used in distant learning web sites or digital library, while illegal copying is prohibited. On the other hand, invisible watermarking is suitable for most forms of digital contents. Users cannot perceptually recognize the difference between invisibly watermarked contents and original ones unless watermark extraction procedures are used. This method conceals both the content of the message (cryptography) and the presence of the message (steganography). An invisible watermark is very difficult to remove. Thereby, this technology could greatly strengthen the enforcement of copyright law on the Internet (Huang, C. and Wu, J.). In this project, we will introduce invisible digital watermarking and its background. We will describe the DCT transform which is an important method applied in the digital watermarking. Then, we will focus on discussing invisible digital watermarking, such as algorithm of digital image watermarking, watermark preprocessing, image embedding, and image extracting. Ultimately, according to the results of implementation, the properties of each algorithm will be analyzed.

2. Background

    Digital watermarking can be used to protect the intellectual property for multimedia data. Digital watermarking has two main advantages: firstly, the authority on a particular file can be traced; secondly, there is no need to use additional space

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    ECE6550 Invisible Digital Watermarking Based on DCT 3

    to maintain this information. A digital watermark is an invisible secret message that is embedded directly in a multimedia file. According to applications, watermarking systems can be classified in fragile and robust. In a fragile watermarking scheme, the watermark is designed to be fragile so as to detect and localize modifications made to the image. Robust watermarking schemes are used for copyright protection. The watermark is designed to be robust against attacks in order to protect ownership of the image. In addition, watermarking systems may be classified in non-blind detection or blind detection which decide whether the detector uses the original image to extract the watermark or not (C. Maria, G. Huiping, M. Luigi and J. Sushil). In our project, we introduce a blind image watermarking system, since only the embedded image and the secret key are required in the detection phase, and the original image is not required.

3. Methods

    3.1 DCT transform

    The discrete cosine transform (DCT) helps separate the image into parts (or spectral sub-bands) of differing importance (with respect to the image's visual quality). The DCT is similar to the discrete Fourier transform: it transforms a signal or image from the spatial domain to the frequency domain, but using only real numbers. There are multiple advantages to using the DCT even better than the Fast Fourier Transform. It has higher compression rate and less error rate. Its basis vectors are comprised of entirely real-valued components which greatly enhance efficiency. Thereby, DCT is important to numerous applications in science and engineering, from lossy compression of audio and images.

    The general equation for a 2D DCT is defined by the following equation:

    ??????:??,????:??:???????????????????????????(????(???? ??????????

The inverse transform is defined as:

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    ECE6550 Invisible Digital Watermarking Based on DCT 4

    ???????????,????:??????????????????????????????(??(?? ??????????

    ???????, ??;And C (u), C (v) = ????????????,??????

    Moreover, there are many advantages of the 2D DCT Transform when N is regarded as 8 or 16. After DCT transform, most of the energy in the image is compressed in the low frequency values in the frequent domain. There are two methods to DCT transform image f (m, n). One is to regard f (m, n) as 2-dimension

    matrix and do DCT transform to f (m, n) directly. Then, embed watermark in the

    image. The other method is conform to the JPEG compression standard, which divides the original image into 8?8 size blocks and do DCT transform to every single block respectively. Then, embed watermark in the image. In this project, we choose the latter methods.

    3.2 Watermarking Preprocessing

    Arnold transformation is a method to preprocess the watermark. It can disorder the image matrix and make the image illegible. However, its excellent periodicity can return the scrambled image to the original one by doing Arnold transformation of one period. One time Arnold transform is shown below:

    ((??????????????;?; ? (?)?(?)??,??????????? ))???

    ? x and y denote the coordinate of pixels of the original watermark, (,~; )?

    denote the coordinate of pixels of the transformed watermark, N denotes the size of original image.

    watermarkArnold Transfer watermark

    To see the example shown above is the original watermark. The right one is the

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    ECE6550 Invisible Digital Watermarking Based on DCT 5

    watermark image after 5 times Arnold transformation

    3.3 Characteristics of Digital Image Watermarking

    1) Visible and Invisible

     Visible watermarking schemes are used to protect digital images or videos, such as contents used in distant learning web sites or digital library, while illegal copying is prohibited. However, invisible watermarking is suitable for most forms of digital contents. Users cannot recognize the difference between invisibly watermarked contents and original image unless watermark extraction procedures are used 2) Fragile and Robustness

     The watermark is designed to be fragile so as to detect and localize modifications made to the image. However, robust watermarking schemes are used for copyright protection. The watermark is designed to be robust against attacks in order to identify ownership of the image

    3) Security

     A strong algorithm applied to the watermark embedding should be able to withstand different attacks and retain the watermark without destroying. 3.4 Flow Diagram of Invisible Digital Watermarking

    Watermarking Watermarking Watermarking

    Embedding Extraction