Digital Image Watermarking Using Different Levels of Intermediate Significant Bits with Zig-zag Embedding Approach

Ali Sharifara, Ghazali Bin Sulong & Mehran Ranjbar Seraydashti
International Journal of Image Processing (IJIP), Volume (7) : Issue (1) : 2013 62
Digital Image Watermarking Using Different Levels of
Intermediate Significant Bits with Zig-zag Embedding Approach
Ali Sharifara a.sharifara@gmail.com
Dept. of Software engineering, faculty of computing
UTM – Malaysia – Skudai 81310
Ghazali Bin Sulong ghazali@spaceutm.edu.my
Mehran Ranjbar Seraydashti rsmehran2@live.utm.my
Abstract
The rapid growths of computer technologies have been increased over the last half century in
terms of amount and complexity of data. Broadcasting of digital contents on the networks
(especially Internet) has become more important and access to the data also has become much
easier than before. Digital watermarking techniques are used to protect the copyrights of
multimedia data by embedding secret information inside them. For example, embedding
watermark in images, audios, and videos. Digital Image watermarking also has been using to
detect original images against forged images by embedding an evidence of the owner of the
digital image. Imperceptibility, on the other hand, is one of the problems in digital image
watermarking which a repeated method in different bit planes of cover image has been presented
to improve the imperceptibility of watermarking in both embedding and extracting processes.
Moreover, embedding process aims to embed watermark in different bit planes by using a non-
sequential method to improve security of image rather than simple sequential embedding.
Keywords: Digital Image Watermarking, Invisible Watermarking, Imperceptibility in
Watermarking, Copyright Protection, Intermediate Significant Bits (ISB).
1. INTRODUCTION
Over the last half century the pace of change in the digital technologies has been widely
increased. Digital images as one of the digital technologies also have been replaced with the
analog images. Moreover, Internet also has become one of the most important tools to transfer
digital images from one part to other parts of the world. For this reason, the security of digital
documents became a challenging concern and digital image watermarking as a solution is use to
decrease the number of digital forged documents.
There are lots of digital images on the Internet without having watermark which can be
downloaded and modified by anyone illegally [1]. Furthermore, the ownership of the image cannot
be traced without the watermarking [2]. Digital watermarking provides a solution in order to
identify the owner of the digital images [3]. It has also been presented for purposes such as:
copyright protection, data authentication, fingerprint, medical applications, and broadcast
monitoring [4]. Image watermarking is the process of embedding an image into a host image [5].
For Instance, watermarks are embedded in bank cheque for preventing forgery. Consequently,
unauthorized modification of data is the concern of researchers about copyright of documents
and numerous image watermarking methods, which have been proposed with different

complexity and efficiency levels so far. Also all of image watermarking methods aimed to set up a
balance between the quality and the robustness of the watermarked images.
One of the most important aspects about the digital image watermarking is to improve the
robustness of the watermarked image [6]. Robustness is related to the ability of recovering the
watermark after performing various processing attacks on watermarked image. The robustness
must be sufficient to handle any kind of attacks occur. The watermarking scheme should be able
to protect the watermark against any possible signal processing operations.
2. WHAT IS WATERMARKING
The growth of the Internet over the last several years has identified the techniques in order to
protect the digital documents in the digital world [7]. Also the Internet has made it easy to
distribute the digital documents such as images, video, and audio [8]. Hence, without having the
powerful techniques for protecting the digital documents, it is impossible to identify the genuine
owner and the plagiarist.
Therefore, the digital watermarking is one of the proper solutions to protect copyright of the digital
documents against forgers. By using watermarking in digital documents, we can reduce the
misusing against the documents such as Will, Cheque and etc. For instance, in the figure 1, an
analog watermarking has been used to protect money against forgers.
FIGURE 1: Example of Analog Watermarking.
Unlike the analog images, all of the images on the Internet are provided as a digital content.
Therefore, a desirable technique for protecting copyright is needed. Digital watermarking can
authenticate the legal copyright and that cannot be removed or manipulated easily by forgers
without having the secure key or other security restrictions. For instance, a duplication of a
cheque can decrease confidence in its authenticity. For this reason, watermarks are employed in
currencies to reduce the risk of forgery. However, the watermark technique is not the only
technique that has been using for preventing forged and illegal uses.
2.1 Proposed Method
Least Significant Bit (LSB) is one of the first techniques for the watermarking purpose and it uses
the lowest bit plane of image [9]. It can modify bits of both host and watermark images to embed
the given watermark. The basic idea behind this technique is the substitution of the lowest bit
plane of the host image with the watermark’s bits. In other words, in the spatial domain, the
watermark is embedded directly into the host image by altering the pixel values [10].
Although, LSB is extremely easy in term of implementation, it is difficult to detect watermark
easily [11]. However, this method is imperceptible and there is no significant difference between
watermarked image and original image, but it is not robustness enough to protect the authority of
watermarked images. This means, in the spatial domain, embedding capacity can be large, but
the watermark could be easily found by unauthorized forgers. The main primary concept of Most

Significant Bit (MSB) is the same as LSB that we have described. The only difference between
them is that, LSB uses the least significant bit, meanwhile in the MSB is completely different and
it uses most significant bits, instead.
When we can say that a watermark method is robust whereby the watermarked image suffers
from different attacks and the embedded image (Watermark) still can be extracted from the
watermarked image [12]. In other words, the attacks must not have any effects in the extraction
process. For example, when a watermarked image is rotated, the algorithm still must identify the
watermark that we have embedded inside the cover image and extract it as well.
2.2 The best quality of image
There is no doubt that the quality of the watermarked image is the most significant parameter in
all invisible methods [13]. In all invisible watermarking methods, the watermark must be
embedded with having the least effect on the quality of the host data. In order to improve the
quality of the watermarked image, beside the security, an Intermediate Significant Bit (ISB)
method has been presented. This means that only some bit(s) – between bit 2 and bit 7 – will be
changed to guarantee the quality of watermarked image which will not have any effect on other
bits.
2.3 The best robustness
Robustness as another concern in watermarking also must be improved [14]. In this research, the
goal is achieved by repeating the embedded bits of watermark for certain times. This idea has
tried to make the algorithm more robust against attacks. Hence, the watermark is encoded into
main signals T times. For instance, in this case we have considered T=3 and image is divided
into blocks with size of 3 pixels, moreover, all of the values of each block should be the same as it
is demonstrated in the figure 2.
FIGURE 2: Divided Cover Image Into Blocks.
To clarify, figure 3 depicts how one pixel of watermark is embedded into the cover image; by this
assumption that the first pixel of watermark contains (11011101), the pattern of embedding is
sequential, and each bit of the watermark image is repeated into the cover image by three times.
Figure 3 shows the result for one pixel of the watermarked image.

Ali Sharifara, Ghazali Bin Sulong
International Journal of Image Processing (IJIP), Volume (7) : Issue (1) : 2013
Extracting process must also
the watermark against attacks and
the attacks. This process verifies
image is to figure out the value of the watermark
for one pixel and makes decision between them. For example, if T=3, (000) represents 0, the
(101) depicts 1, the (001) represents 0 and so on. To improve the robustness of the watermarked
image, one bit in each pixel can be embedded in a block of pixels
one pixel. This method has some advantages and disadvantages as well. The most important
disadvantage of this method is
embedded in the host image. On the other han
by increasing the size of each block. Moreover, each block can be divided into 3, 5, 7, and 9
pixels as can be seen from the figure 4.
Beside the improvement of robustness in the watermarking system, other parameters also need
to be improved such as securit
Hence, a few steps are required
method is more robust and secure as well. Security beside the robustness is also
important point which may help to cut
all of these stages can be executed separately. In the following se
discussed.
2.4 Security in Watermarking
Security is a vital parameter in the watermarking system which must be considered as well [15].
The main aim of the attack in terms of security is to obtain the secret key of encoding
well as decoding [16]. This means a strategy must be used to protect
malicious users and this strategy must be hidden. In other words, the watermark must
enough to be protected from the people those
Ghazali Bin Sulong & Mehran Ranjbar Seraydashti
Image Processing (IJIP), Volume (7) : Issue (1) : 2013
FIGURE 3: Repeating Bits in Each Block.
also be done in order to reverse this process. This procedure protects
watermark against attacks and it can decrease the risk of losing bits that can be damage
the attacks. This process verifies the majority of bits while extracting watermark
the value of the watermark. In other words, the algorithms read all three bi
decision between them. For example, if T=3, (000) represents 0, the
image, one bit in each pixel can be embedded in a block of pixels instead of embedding in only
disadvantage of this method is the decreasing of the size of the watermark data which can be
embedded in the host image. On the other hand, this approach makes an acceptable robustness
pixels as can be seen from the figure 4.
FIGURE 4: Repeating Bits in Each Block.
robustness in the watermarking system, other parameters also need
such as security and capacity of image which can hide the
are required to be developed which can provide guarantee that the proposed
hod is more robust and secure as well. Security beside the robustness is also
may help to cut-off the attacks of malicious users. It is important to note that
all of these stages can be executed separately. In the following section more details have been
Security in Watermarking
attack in terms of security is to obtain the secret key of encoding
This means a strategy must be used to protect the
this strategy must be hidden. In other words, the watermark must
be protected from the people those do not have the right to modify or manipulate the
Image Processing (IJIP), Volume (7) : Issue (1) : 2013 65
this process. This procedure protects
can decrease the risk of losing bits that can be damaged by
the majority of bits while extracting watermark from the host
. In other words, the algorithms read all three bits
decision between them. For example, if T=3, (000) represents 0, the
instead of embedding in only
the size of the watermark data which can be
d, this approach makes an acceptable robustness
robustness in the watermarking system, other parameters also need
the information inside.
guarantee that the proposed
hod is more robust and secure as well. Security beside the robustness is also another
off the attacks of malicious users. It is important to note that
ction more details have been
attack in terms of security is to obtain the secret key of encoding process as
the watermark against
this strategy must be hidden. In other words, the watermark must be secured
right to modify or manipulate the

watermarked image. In addition, the security in watermarking is represented same as security
techniques which have been used in encryption methods [15].
2.4.1 Zig-Zag embedding matrix
To improve the security of watermarked image, a non-sequential algorithm is needed. A Zig-zag
array is a square collection of the first N^2 integers and the numbers increase sequentially as can
be seen from the figure 5. Therefore, the watermark pixels are not sequential and the watermark
cannot be easily extracted by unauthorized users [17]. Beside, Zig-Zag embedding method we
have used a secret key to guarantee through which our embedding method is secure enough.
FIGURE 5: Zig-Zag Embedding Matrix [17].
2.5 The chosen attacks
Some attacks which might target the images and make effects on them. Some of them are
provided. Such attacks include: Gaussian filter, Speckle noise, Salt and Pepper, Passion, and
Blurring.
2.6 Experimental data analysis
By using two techniques, which have been mentioned above, for improving robustness and
security, we have come up with results provided in the table 1. The result illustrates PSNR for
different bit planes in proposed method.
Bit Planes PSNR Bit Planes PSNR
1,2,3 45.7101 3,4,5 33.2965
1,3,4 39.8263 3,5,6 31.7147
2,3,4 39.6664 4,5,6 31.3294
2,4,5 33.4402 5,6,7 30.1412
Table 1: Different Bit Planes with Their PSNR Values of Proposed Method.
In the Table 2, some selected methods have been compared with one group of bit planes in the
proposed method. As it can be seen from the table 2, the proposed method has the best quality
among others after embedding the watermark.

Methods PSNR
Proposed Method 45.71
HPDM 36.42
ST-SCS 36.42
color-based-encoding 30.48
Side match method 41.22
PVD 41.79
Conventional LSB 31.71
DCT 31.847
Vulnerability of PVD 45.1
Table 2: Comparison Between Different Methods [19].
2.7 Extracted Watermark after performing selected attacks
As it can be inferred from the table 2, the proposed method is more robust in comparison with
conventional LSB and MSB methods. Nevertheless, most of the image attacks tend to destroy
low bits (1, 2, and 3), but the proposed method can extract the watermark after the attacks by
acceptable percentage of healthy pixels in the watermark even in the low bit-planes [18].
Surprisingly, as can be seen from the result of proposed method, the average PSNR in all of the
8 layers are approximately same by over 30 db. Hence, the above result proves that the
watermark can embed into all bit-planes of cover image regardless of the visibility of the
watermark.
The below figures also provides information about the PSNR of the watermark after extraction for
proposed method compared to the conventional LSB method. The x-axis indicates 8 bit-planes
and the PSNR is indicates on y-axis.
FIGURE 6: Applied Salt and Pepper Attacks for Both Proposed and Conventional LSB Method.

FIGURE 7: Applied Blurring Attacks for Both Proposed and Conventional LSB Method.
As can be seen from the figure 6 and 7, the selected attacks do not have any significant effect on
the watermark and can be extracted by high PSNR (Peak signal-to-noise ratio). Furthermore,
other two mentioned attacks also have less effect on the watermark image after extraction in all
different 8 bit planes. Table 3 and 4 show the watermark images after extracting in both proposed
method and the conventional LSB, respectively.
Bit- planes Salt and Pepper Gaussian Speckle Poisson Blurring
1,2,3
PSNR 57.8942 35.1767 35.1767 35.1211 35.1767
1,3,4
PSNR 58.0278 33.1767 35.1767 31.9604 30.2204
2,3,4
PSNR 58.0448 29.2292 28.8208 29.1933 28.9032
2,4,5
PSNR 54.8024 29.1511 29.0914 29.2553 28.7651
3,4,5
PSNR 57.1409 29.0285 29.7285 28.9973 28.2251
3,5,6
PSNR 55.2978 28.9489 29.7255 29.9973 29.0686
4,5,6
PSNR 55.2978 28.8878 31.5728 30.5728 28.9786
Table 3: Extracted Watermark After Attack in Proposed Method.

The result proves that the watermark can embed into all bit-planes of the cover image regardless
of the visibility of the watermark. We also have performed similar tests to other images and we
have achieved the same results.
Bit- Planes
Salt and
Pepper
Gaussian Speckle Poisson Blurring
1
PSNR 41.3402 27.2872 27.4521 27.2553 27.3459
2
PSNR 40.9581 27.4718 27.5265 27.3376 27.4557
3
PSNR 42.6408 27.2759 27.3816 27.3793 27.2623
4
PSNR 41.3980 27.3839 27.5088 27.4279 27.7070
5
PSNR 41.3206 27.4665 29.5288 27.8759 27.8265
6
PSNR 41.6746 27.6354 32.2871 29.7421 28.2866
7
PSNR 41.8143 29.4687 34.7684 32.8219 27.4516
8
PSNR 40.7806 32.2926 39.5445 36.0818 27.4319
Table 4: Extracted Watermark After Attack in Conventional Method LSB.

3. CONCLUSION AND FUTURE WORK
Watermarking is a method that is being used to hide information or identify data within the digital
documents. Moreover, digital documents can be divided into three categories: video, audio and
image. In this research, we have focused primarily on the watermarking of digital images. Digital
watermarking is becoming popular, mainly for embedding undetectable marks such as copyright
information. In this research, gray scale images have been applied to embed as an evidence of
the ownership for the digital images. The proposed method also used Intermediate Significant
Bits (ISB) to improve the quality of the watermarked image.
In this research, we have proposed a new watermarking method to improve previous works in
area of spatial domain in terms of robustness and imperceptibility. The proposed method has
been aimed to improve robustness of the watermarked image by using repeated variable for each
pixel of the watermark. Also, it improves the probability of extracting intact bits after attacks and
the security guaranteed by using a secret key and none-sequential embedding method.
Although the proposed method is tried to achieve the best quality, robustness, and security for
watermarking in grayscale images, but some other important parameters must be considered as
well, such as: Capacity and Integrity. Also grayscale image has been used for this research, but
the present study can also be extended for colored image (RGB).
4. REFERENCES
[1] Chin-Shiuh Shieh, Hsiang-Cheh Huang, Feng-Hsing Wang, Jeng-Shyang Pan,“Genetic
watermarking based on transform-domain techniques”. Pattern Recognition,. 37(3): p.
555-565, 2004.
[2] Golea, N.E.-H., “A bind RGB color image watermarking based on singular value
decomposition”, in Proceedings of the ACS/IEEE International Conference on Computer
Systems and Applications - AICCSA 2010, IEEE Computer Society. p. 1-5. 2010.
[3] Yongjian Hu,Guangzhou, China Kwong, S. “Using invisible watermarks to protect visibly
watermarked images” ,p. 584-587. 2004.
[4] Potdar, V.M., Han, S.,Chang, “A survey of digital image watermarking techniques”. 2005.
p. 709- 716.
[5] Bamatraf,A.Ibrahim,R.Salleh, M.N.B.M, “Digital watermarking algorithm using LSB”, in
Computer Applications and Industrial Electronics (ICCAIE), Kuala Lumpur, 2010.
[6] Dharwadkar, N.V., Amberker, B.B,Gorai, A., “Non-blind watermarking scheme for color
images in RGB space using DWT-SVD”, in Communications and Signal Processing
(ICCSP), 2011 International Conference, Calicut, 2011.
[7] Dehkordi, A.B., Esfahani, S.N., Avanaki, A.N. , “Robust LSB watermarking optimized for
local structural similarity”, in Electrical Engineering (ICEE), 2011 19th Iranian Conference.
Tehran, 2011.
[8] Arya, D.,“A Survey of Frequency and Wavelet Domain Digital Watermarking
Techniques”. 2010. 1(2).
[9] Zhao Xingyang, “A novel color image fragile watermarking based on the extended
channel”, in Broadband Network & Multimedia Technology, 2009. IC-BNMT '09. 2nd
IEEE International Conference, Beijing, Oct. 2009.

[10] Gil-Je Lee, “A New LSB Based Digital Watermarking Scheme with Random Mapping
Function”, in Ubiquitous Multimedia Computing. UMC '08. International Symposium:
Hobart, ACT, Oct 2008.
[11] Ker, A., “Improved Detection of LSB Steganography in Grayscale Images Information
Hiding”, J. Fridrich, Editor, Springer Berlin / Heidelberg, 2005.
[12] Kumar, N.M., Manikandan, T.,Sapthagirivasan, V. , “Non blind image watermarking
based on similarity in contourlet domain”, in Recent Trends in Information Technology
(ICRTIT), 2011 International Conference, Chennai, Tamil Nadu, 2011.
[13] Maity, S.P. and M.K. Kundu, “DHT domain digital watermarking with low loss in image
informations”. AEU - International Journal of Electronics and Communications. 64(3): p.
243-257,2010.
[14] MohammadReza Keyvanpour, Farnoosh Merrikh Bayat, “Blind image watermarking
method based on chaotic key and dynamic coefficient quantization in the DWT domain”,
Mathematical and Computer Modelling, Available online 27 July 2012, ISSN 0895-7177,
2012.
[15] Hu, M.-C., D.-C. Lou, and M.-C. Chang, “Dual-wrapped digital watermarking scheme for
image copyright protection". Computers & Security 26 (4) , 319-330, 2007.
[16] Jian Cao; Jiwu Huang; , "Controllable Secure Watermarking Technique for Tradeoff
Between Robustness and Security," Information Forensics and Security, IEEE
Transactions on , vol.7, no.2, pp.821-826, April 2012.
[17] M.Padmaa, “ZIG-ZAG PVD – A Nontraditional Approach”. International Journal of
Computer Applications. Volume 5– No.7, August 2010.
[18] Mir Shahriar Emami , Ghazali Bin Sulong, “Set Removal Attack: A New Geometric
Watermarking Attack” in 2011 International Conference on Future Information
Technology IPCSIT. 2011, IACSIT Press: Singapore. 2011.
[19] Akram M. Zeki. Khedher, Azizah Abdul Manaf. “Digital watermarking and data hiding
techniques”. Proceedings of the Postgraduate Annual Research Seminar p. 79-84, 2006.

Digital Image Watermarking Using Different Levels of Intermediate Significant Bits with Zig-zag Embedding Approach

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