Image Watermarking Techniques in Spatial Domain: A · PDF fileImage Watermarking Techniques in Spatial Domain: ... Abstract . The rapid growth of digital multimedia technologies

Image Watermarking Techniques in Spatial Domain: A Review Alankrita Aggarwal Monika Singla Sr .Assistant Professor Department of M.Tech Student Department of Computer Computer Science and Engineering ,Haryana Science and Engineering,Haryana Collegeof College Of Technology and Management, Technology and Management, Kaithal,India Kaithal,India [email protected] [email protected]

Abstract

The rapid growth of digital multimedia technologies brings tremendous attention to the field of digital watermarking. The owner or the distributor of the digital images can insert unique watermark into copies for different customers or receivers, which will be helpful to identify the source of illegal copies. Watermarking embeds a secret message into a cover multimedia data. In media watermarking the secret is usually a copyright notice and the cover a digital image. In digital watermarking, robustness is still a challenging problem if different sets of attacks needed to be tolerated simultaneously. Many algorithms have been developed for check the robustness of images In this paper we are reviewing spatial watermarking technique for digital images like LSB technique, BLOCK based and Secure watermarking techniques. Keywords: Color Image, Spatial Domain, Robust Watermarking

1. Introduction A digital watermark is a digital signal or a pattern

embedded into the host media to be protected, such as an image or audio or video. It contains useful certifiable information for the owner of the host media, such as producer's name, company logo, etc; the watermark can be detected or extracted later to make an assertion about the host media. There are two important properties of a watermark; the first is that the watermark embedding should not alter the quality and visually of the host image and it should be perceptually invisible, the second property is robustness with respect to image distortions. This means that the watermark is difficult for an attacker to remove and it should be also robust to common image processing and geometric operations, such as filtering, resizing, cropping and image compression. Overviews on image watermarking techniques can be found in [1],[2], [5] .

1.1. Domain of watermarking The watermarking techniques can be classified into two categories: spatial domain and transform domain techniques. There definitions are as follow

1.1.1. Spatial domain. In spatial domain technique [4], [7], [10], [11], [12], [14], the watermark embedding is achieved by directly modifying the pixel values of the host image. The most commonly used method in the spatial domain technique is the least significant bit (LSB). In the least significant bit (LSB) of each pixel in the host image was modified to embed the secret message. 1.1.2. Transform domain. In transform domain technique[2],[3]the host image is first converted into frequency domain by transformation method such as the discrete cosine transform (DCT), discrete Fourier transform (DFT) or discreet wavelet transform (DWT) ,etc. then, transform domain coefficients are altered by the watermark. The inverse transform is finally applied in order to obtain the watermarked image. The frequency domain methods allow an image to be broken up into different frequency bands. Embedding the watermark in the low frequency increases the robustness with respect to image distortions. The high frequency band of an image is more prone to dropping due to quantization and it will be lost by compression or scaling attacks. The middle frequencies embedding of the watermark avoid the most visual important parts of the image and it is robust to compression and noise attacks. There are so many ideas have been proposed for placing key inside the binary images or watermark image [10], [4].

We discussed a spatial domain block based watermarking scheme, LSB technique and secure watermarking technique. The watermark is a binary image, which is permuted using a secret key.

Monika Singla et al, Int. J. Comp. Tech. Appl., Vol 2 (5), 1357-1363

IJCTA | SEPT-OCT 2011 Available [email protected]

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Watermark w Or original image Detection Text image Watermark

Secret/public key

Detection algorithm

2. General framework for digital watermarking

Watermark is a digital signal or pattern inserted into a digital data, which can also be referred to as a digital signature. Watermarking is a key process in the protection of copyright ownership of electronic data, including image, videos, audio, etc

Any watermarking scheme (algorithm) consists of three parts:

(a) The watermark (b)A watermark embedder (marking insertion

algorithm) (c)A watermark detector (verification or extraction

or detection algorithm). 2.1. Embedding watermark

The watermark signal, apart from depending on the watermark information W', may also depend on a key K and the host data I into which it is embedded, shown in Equation

W = f 0(I, K, W’)

Watermark

Digital Data Watermarking Watermarked Data

Secret/Public key

Figure 1.Generic watermarking embedded scheme

2.2. Extracting watermark Verification algorithm is a design of the

corresponding extraction method that recovers the watermark information from the signal mixture, perhaps with the help of the key and the original shown in Equation (1) or (2)

I0 = g (I, I', K) (1) Or without the original

I0 = g (I', K) (2) The input to the scheme is the watermark, the host

data, and an optional public or secret key. The host data may, depending on the application, be uncompressed or compressed, however, most proposed methods work on uncompressed data. The watermark can be of any nature, such as a number, text, or an image. The secret or public key is used to enforce security. If the watermark is not to be read by unauthorized parties, a key can be used to protect the watermark. In combination with a secret or a public key, the

watermarking techniques are usually referred to as secret and public watermarking techniques, respectively.

Figure 2.Generic watermarking recovery scheme

3. Attacks on watermark

It is found in the literature that the robust watermarking systems proposed so far can only withstand some of the possible external attacks but not all. The attacks against the watermark try to neutralize the watermark, without damaging the image too much. The watermark is neutralized if: (a) the detector cannot detect the watermark (distortion, attenuation etc.), (b) the detector cannot recognize the watermark in the image from another one, and (c) the watermark is no longer in the image.In the field of digital watermark, there are various categorizations of attacks on watermarks .

3.1. Unintentional attacks

3.1.1. Compression. Many compression schemes

like JPEG and MPEG can potentially degrade the data’s quality through irretrievable loss of data.

3.1.2.Geometricdistortions. Geometric distortions

are specific to Images videos and include such operations as rotation, translation, scaling.

3.1.3.Common Signal Processing Operations. it

includes D/A conversion, A/D, conversion, Resembling.

3.1.4. Cropping . The watermarked image is cropped

in terms of percentage of image size. The effect of cropping is decided calculating the NC and SC between extracted watermark and original watermark.

3.2. Intentional attacks 3.2.1 Collusion . A number of authorized recipients of the image should not be able to come together (collude) and like the differently watermarked copies to generate



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an unwatermarked copy of the image (by averaging all the watermarked images).

3.2.2 Forgery. A number of authorized recipients of the image should not be able to collude to form a copy of watermarked image with the valid of embedded watermark of a person not in the group with an intention of framing a 3rd party.

3.2.3. IBM attack. It should not be possible to produce a fake original that also performs as well as the original and also results in the extraction of the watermark as claimed by the holder of the fake original

4. Existing techniques Image watermarking became popular in the 1990s.

The most important aspect of image watermarking is roubustness. The number of image watermarking techniques has been developed in spatial domain which considered the roubustness. Watermarking methods differ only in the part or single aspect of three topics

• Signal design • Embedding • Recovery A Digital image is a 2-D Signal. It Use rectangular

shape areas called pixels. Intensity value of pixels are represented as I(X,Y). Here pixel resolution is described with the set of two positive integer numbers, where the first number is the number of pixel columns (width) and the second is the number of pixel rows. Color image is a combination of three frames i.e. Red, Green, Blue frames.The first technique in spatial domain is tagging technique. A tag is a square of size N * N. In a first step, all possible locations in an image where a tag could possibly be placed are identified by calculating the local region variance of size N * N in the image and comparing it to empirically identified upper and lower limits. A selected image area is tagged by adding the tag. One selected tag location hides 1 bit and is only tagged if the bit to embed is set to one. To recover an embedded bit, the difference between the original and the tagged image is computed.There was so many techniques has been introduced .Here we are dicussing some new one which discussed below. 4.1. LSB technique

The most straightforward method of watermark embedding would be to embed the watermark into the least significant bits of the cover object. Fig. 3.1 shows an example of modifying LSB. Image: 11001010 00110101 00011010 00000000 ...

Watermark: 1 1 1 0 ... Watermarked 11001011 00110101 00011011 00000000… .

Image:

Figure 3 Example of Least significant bit watermarking 4.2.Secure watermarking scheme for color image

The proposed scheme is of type blind and invisible watermarking. This scheme introduces the concept of storing variable number of bits in each pixel based on the actual color value of pixel. Equal or higher the color value of channels with respect to intensity of pixel stores higher number of watermark bits. The Red, Green and Blue channel of the color image has been used for watermark embedding. The watermark is embedded into selected channels of pixel. The proposed method supports high watermark embedding capacity, which is equivalent to the size of cover image. The security of watermark is preserved by permuting the watermark bits using secret key. The algorithm is explained in the following sections.

4.2.1 Watermark Embedding.Embedding the watermark requires the following steps.

Input: Color (Cover) Image (C) and Monochrome Watermark image (W). Step 1. Read the watermark image W of size m×m Step 2. Read a binary key k which is the secret key and compute W'=W K, where is bit wise XOR operator. Step 3. Read the color image C of size m×m and transfer this image into Red (R), Green (G) and Blue (B) channels of size m×m. Then transfer these R, G, B channels into biological color model Hue (H) Saturation (S) and Intensity (I) using the following equations.

θ if B ≤ G H = 360 −θ if B > G (3) S = 1 - 3 min(R,G, B) (4) ( R+G+B) (R + G + B) I = (5) 3

Step 4. For each pixel select a channel from R, G, B which is having value ≥ I and embed the watermark bit of W’ into LSB of selected channels using LSB substitution. Step 5. Transfer the modified R, G, B channels into watermarked color image C '. 4.2.2. Watermark Extraction.Algorithm : Watermark Extraction.Input : Watermarked Color Image (C and the secret key (K).



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Step 1.Read the watermarked color image C of size m×m and transfer this image into Red(R '), Green (G') and Blue (B') channels of size m×m. Then transfer these R', G', B' channels into biological color model Hue (H'), Saturation (S') and Intensity (I') using the equations (3), (4) and (5). Step 2. Read a binary sequence K which is the secret key. Step 3. For each pixel select a channel from R', G', B' which is having value ≥ I ' and extract the watermark bit W’ from LSB of selected channels. Step 4. Process the W ' with key array K to get the extracted watermark W as follows: W=W' K, where is bit-wise XOR operator.

The performance of extraction algorithm is analyzed by increasing density of the noise compared in terms of NC and SC. The increase in the noise density reduces the performance of extraction algorithm. The watermarked image is cropped in terms of percentage of image size.The proposed watermarking algorithm is robust for cropping on the set of watermarked images. The algorithm is rigid for upto 40 % cropping. The watermarked image is compressed with different Quality factors. The effect of compression is observed by calculating the NC and SC between extracted watermark and original watermark. As the compression factor increases the quality of extracted watermark decreases. Thus algorithm is robust against compression of quality factor upto 50. Security of watermark can be further enhanced by using hash functions or chaotic binary sequence. The proposed algorithm is weak to geometrical transformation. Thus the future work is to design a geometrical transform-invariant watermarking algorithm.

4.3. A New robust watermarking scheme for color image in spatial domain

A robust watermark scheme based on a block probability for color image is presented, which operates in spatial domain by embedding the watermark image four times in different positions in order to be robust against attack The extraction of the watermark depends on the original image, so it is a non-blind watermarking scheme. In the proposed method, the watermark image is a binary image where as the host image is an 8 bit color image. The four embedded positions are chosen to hide the watermarks in order to be robust against cropping attack from the bottom, the top or the left or the right side of the watermarked image. The blue component is chosen to hide the watermark because it is less sensitive to human eyes. The original color image H with size of 512*512 pixels, which to be protected by the binary watermark W of size pixels

32*32 .The Embedding and extraction algorithm is explained in the following sections.

4.3.1 Watermark embedding. Step 1. A binary logo

image is used as the original watermark W of size pixels 32*32. The original watermark is permuted to obtain a pseudo random sequence, which uncorrelated to the original watermark. This is done by performing bit wise EX-OR operation between the original watermark bits and random bits, generated using a secret key, and then the output sequence, is encoded using Gray which code. The permutation process of the Watermark W is described as follows:

Read a binary key k which is the secret key and compute W'=W K, where is bit wise XOR operator. Step 2. The original image H is decomposed into R, G, and B components and then the B component is divided into a non-overlapping blocks with size of 8*8 pixels. Step 3. Private key is used to determine the positions of embedding the watermark. Step 4. The encoded watermark W'' is embedded in the blue component B. For each encoded watermark bit, a block of 8*8 is modified as follows:

if W''=1; for all the pixels of the 8*8 blocks

{I'=I+ λ} If W''=0; For all the pixels of the 8*8 blocks

{I'=I- λ} Where I' is the modified pixel intensity and I is the original intensity and λ is a constant. Step 5 The modified block of pixels is then positioned in its original location of the host image and then step 3 and 4 is repeated until all encoded watermark bits W'' are embedded. Step 6 After embedding the all encoded watermark bits four times, the R, G, and B' components are composed to obtain the watermarked image.

1 128 384 512

128

384 512 Fig 4 The proposed watermarks embedded positions

Watermark 1

Watermark3 Watermark4 Waterm3

Watermark 2



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4.3.2 Watermark extraction .The proposed watermark extraction required the original host image and the original watermark, therefore, it is a non blind watermarking scheme. The steps of watermark extraction are described below. Step 1. The proposed extraction is based on the probability (P1, P0) of detecting '1' or '0' bit, which can be obtained by comparing each pixel (I') in a block of 8*8 of the watermarked image with the corresponding pixel (I) in the original image and then the probability is calculated as follows:

P1=P1+1/64 if I' > I P0=P0+1/64 if I' ≤ I Step 2. According to the probability (P1, P0), the extracted watermark bits W'' can be decoded as follows:

W′′ = 1 if P1 ≥ P0 W′′ = 0 if P1< P0 Step 3. The extracted watermark bits for the four watermarks are decoded using Gray code and then, the decoded bits are XOR with random bits, which generated using the same secret key that was used during the watermark embedding. The decoded watermarks bits are reordering to images W'1, W'2, W'3, W'4. Step 4. we calculate the normalized cross correlation between the original watermark image W and the extracted watermarks W'1, W'2, W'3, W'4 to make a binary decision on whether a given watermark exists or not. We choose 0.5 as the threshold for watermark decision. Step 5. The normalized cross correlation is defined by ∑ ∑ Wi jW'i j i j NCC= ∑ ∑ (Wij)2 i j

Where W i j and W' i j are the pixel values at the position (i, j) of the original and the extracted watermark. This scheme is highly robust against various of image processing operations such as, filtering, cropping, scaling, compression, rotation, randomly removal of some rows and columns lines and salt and paper noise. 5. Conclusion In this paper, spatial domain watermarking techniques for color Images are discussed .LSB is proved to be simple and powerful tools for Steganography but lack the robustness.In case of secure watermarking technique, the security of watermark is preserved by permuting the watermark bits using secret key. The increase in the noise density and compression factor reduces the performance of extraction algorithm. The

algorithm is rigid for upto 40 % cropping.But in case of a New Robust Watermarking Scheme for Color Image in Spatial Domain,cropping results are better but algorithm is weak to geometrical transformation attack such as rotation, translation, scaling.To get better result in case of noise attack,we can place watermark at five different positions and used another image as a key in watermark to increase security . 6. References [1] W. Bender,D.Gruhl,N.Mormoto, and A.Lu,”Techniques for data hiding”, IBM Systems Journal, vol. 35, no 3 pp 313-336, 1996. [2] F. Hartung and M. Kutter, "Multimedia watermarking techniques," Proceedings of the IEEE, vol. 87, pp. 1079-1107, 1999

[3] Hsiang-Kuang Pan, Yu-Yuan Chen, and Yu-Chee Tseng, “A Secure Data Hiding Scheme for Two-Color Images”, in Fifth IEEE Symposium on Computers and Communications, pp. 750 – 755, July 2000.

[4] M. Wu, E. Tang, and B. Liu, “Data hiding in digital binary image,” Electrical Engineering Dept., Princeton Univ., Princeton, NJ 08544,Electrical & Computer Engineering Dept., John Hopkins Univ., Baltimore, MD 21218 in Proc. Of IEEE Int. Conf. on Multimedia and Expo, New York City, pp. 393-396, July 31 to August 2, 2000

[5] G. C. Langelaar, I. Setyawan, and R. L. Lagendijk,"Watermarking digital image and video data. A state of the-art overview," Signal Processing Magazine,IEEE, vol. 17, pp. 20-46, 2000.

[6] H.Ren-Junn, K. Chuan-Ho, and C. Rong-Chi, "Watermark in color image," Proceedings of the first International Symposium on Cyber Worlds, pp. 225-229, 2002.

[7] S. Kimpan, A. Lasakul, and S. Chitwong,"Variable block size based adaptive watermarking in spatial domain," presented at Communications and Information Technology, ISCIT 2004. IEEE International Symposium on, vol. 1, pp. 374-377, 2004.

[8] Feng-Hsing Wang, Lakhmi C. Jain, Jeng-Shyang Pan, “Hiding Watermark in Watermark”, in IEEE International Symposium in Circuits and Systems (ISCAS) ,Vol. 4, pp. 4018 – 4021, May 2005

[9] Juan Jose Roque, Jesus Maria Minguet “SLSB: Improving the Steganographic Algorithm LSB “Universidad Nacional de Educación a Distancia, 2006.

[10] B. Verma, S. Jain, D. P. Agarwal, and A.Phadikar, "A New color image watermarking scheme," Info comp, Journal of computer science , vol. 5,No.2, pp. 37-42, 2006.

[11] X. Wu and Z.-H. Guan, "A novel digital watermark algorithm based on chaotic maps," Department of Control Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR Chinab School of Electronics and information, Yangtze University, Jingzhou, Hubei 434023, PR China, Science Direct, Physics Letters A, vol. 365, pp. 403-406, 2007.

[12] Ibrahim Nasir, Ying Weng, Jianmin Jiang, “A New Robust Watermarking Scheme for Color Image in Spatial Domain”, School of Informatics, University of Bradford, UK 2008.



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[13] Nagaraj V. Dharwadkar and B. B. Amberker ,”Secure Watermarking Scheme for Color Image Using Intensity of Pixel and LSB Substitution”, journal of computing, volume 1, issue 1, ISSN: 2151-9617, December 2009 . [14] V.Madhu Viswanatham, Jeswanth Manikonda, “Novel Technique for Embedding Data in Spatial Domain “,School of Computing Science and Engineering, VIT University, Vellore, India, International Journal on Computer Science and Engineering Vol. 2pp.233-236,2010.



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Image Watermarking Techniques in Spatial Domain: A · PDF fileImage Watermarking Techniques in Spatial Domain: ... Abstract . The rapid growth of digital multimedia technologies