Data Hiding Method With High Embedding Capacity Character

Wen-Chung Kuo, Jiin-Chiou Cheng & Chun-Cheng Wang
International Journal of Image Processing (IJIP) Volume(3), Issue(6) 310
DATA HIDING METHOD with HIGH EMBEDDING CAPACITY
CHARACTER
Wen-Chung Kuo simonkuo@nfu.edu.tw
Department of Computer Science and
Information Engineering,
National Formusa University,
Yunlin 632, Taiwan, R.O.C
Jiin-Chiou Cheng chiou@mail.stut.edu.tw
Southern Taiwan University,
Tainan 710, Taiwan, R.O.C
Chun-Cheng Wang 96g0216@webmail.stut.edu.tw
Southern Taiwan University,
Tainan 710, Taiwan, R.O.C
Abstract
Recently, the data hiding method based on the high embedding capacity by using
improved EMD method was proposed by Kuo et al.[6]. They claimed that their scheme can
not only hide a great deal of secret data but also keep high safety and good image quality.
However, in their scheme, the sender and the receiver must share the synchronous
random secret seed before they transmit the stego-image each other. Otherwise, they can
not recover the correct secret information from the stego-image. In this paper we propose
an improved scheme based on EMD and LSB matching method to overcome the above
problem, in other words, the sender does not share the synchronous random secret seed
the receiver before the stego-image is transmitted. Observing the experimental results,
they show that our proposed scheme acquires high embedding capacity and acceptable
stego-image quality.
Keywords: Data-hiding, Cover-image, Stego-image, EMD, LSB match method.
1. Introduction
With the rapid development of network technology, vast multimedia data would be communicated over the
network. Although network transmission is convenient and fast, the multimedia data passing through the
network is often attacked and tampered by malicious attackers. From the literatures many people are devoted
to study the security for multimedia data. In general there are two methodologies to deal with such work: one
is the cryptography and the other is steganography. Using the cryptography methodologies, the only specific
user with the private key can decrypt the ciphertext when the plaintext is encrypted. An attacker cannot find
out the content of message even though he gets the encryption message from the Internet. Nevertheless, the
ciphertext will still be insecure if the private key is stolen or broken. Another way to promote the security of
multimedia data is to hide secret data behind a meaningful image. The major goal of data hiding scheme is

not only to raise the hiding amount in the stego-image but also keep the quality of the stego-image. In the past
literatures, many well data-hiding schemes had be suggested [4,6,9].
In 2006, an efficient embedding scheme based on the Exploiting Modification Direction (for short, EMD-
scheme) was proposed by Zhang and Wang [9]. The scheme uses the relationship of adjacent pixels to
embed the secret data. The secret data will be embedded within two adjacent pixels, that is, only one of two
pixels in the EMD scheme – add one, subtract one, or stay the same. From a spatial point of view, two pixels
just have five situations - moving upward, downward, left, right, or not moving at all. From their experimental
simulations and discussions, the EMD-scheme can enhance the capacity of secret message and the quality of
the stego-image. Recently, Lee et al. [4] proposed an improved data-hiding scheme, say LWC-scheme, which
catches both of two adjacent pixels at a time and improves the possible situations from five to eight. As a
result of LWC-scheme, it can promote the capacity 1.5 times approximately the former. Since the data
embedding process uses the fixed evaluating parameters in both of EMD-scheme [9] and LWC-scheme [4],
they will be cracked easily and leak the secret message within the stego-image while their technology are
disclosed. Therefore, some concerns about the security issues will be considered. Later, Kuo et al. (for short
KWSK-scheme) [6] proposed two high capacity EMD data hiding techniques with changing-evaluating-value
to improve the shortcoming of above schemes, in other words, the stego-images will still be safe even when it
publishes the embedding formulas. According to KWSK-scheme, they used the synchronous generator of
random numbers to minimize the possibility of message disclosure and improve the lack of open method but
there is an open problem of synchronization of random seeds before the stego-image is transmitted between
the sender and the receiver. In this paper, we will propose an improvement scheme based on EMD and LSB
matching method to overcome the synchronization problem, in other words, the sender does not send the
synchronous random secret seed to the receiver before the stego-image is transmitted. According to the
experimental simulations and discussions, we show that the proposed scheme still keeps high safety and
good image quality.
The rest of this paper is organized as follows. In Section 2, we will introduce the EMD-method, LSB matching
method and LWC-scheme briefly. Then, we will propose the improvement scheme to overcome the
synchronization problem and give the experimental result in Section 3 and Section 4, respectively. Finally,
conclusions will be drawn in the Section 5.
2. REVIEW THE DATA HIDING SCHEME WITH HIGH EMBEDDING CAPACITY
TECHNIQUES
2.1. The Exploiting Modification Direction Method
In 2006, Zhang and Wang [9] used the relationship of adjacent pixels to promote the data embedding
scheme. In their method, they transfer the secret message into (2n+1)-ary system and then embed the
modified secret message into a group of n pixels in cover image by using the following equation:
( ) ( ) ( ) (1)12mod,,
1
21 +





⋅= ∑=
niggggf
n
i
inL
gi is the i-th value of pixel and n is the number of pixels. Due to the limit of paper page, we cannot explain their
embedding and extracting procedures in detail here. For more details about those methods, the reader can
refer to the Ref. [9].
2.2. The High Embedding Capacity by Improving Exploiting Modification Direction (EMD)
According to Lee et al.’s analysis, they find only five situations - moving upward, downward, left, right, or not
moving at all to embed the secret data into two adjacent pixels by using the EMD scheme. To elevate the
capacity of EMD-scheme, Lee et al. improve the number of variable situations from five to eight and then
propose a steganographic scheme [4] with high embedding capacity in 2007. Here, we just only describe the
embedded procedure in LWC-scheme as following steps:
Step 1. Transfer the secret message to message s, which is 8-ary system.
Step 2. Take two adjacent pixels (X, Y) as a group and perform the following extraction process,
( ) ( ) (2)8mod31, ×+×= YXYXfe
Step 3. Adjust (X, Y) according to the following rule:
（3-1） If s = fe(X,Y), X = X, Y = Y.
（3-2） If s = fe(X+1,Y), X = X+1.

（3-3） If s = fe(X-1,Y), X = X-1.
（3-4） If s = fe(X,Y+1), Y = Y+1.
（3-5） If s = fe(X,Y-1), Y = Y-1.
（3-6） If s = fe(X+1,Y+1), X = X+1, Y = Y+1.
（3-7） If s = fe(X+1,Y-1), X = X+1, Y = Y-1.
（3-8） If s = fe(X-1,Y+1), X = X-1, Y = Y+1.
Therefore, the stego-image may be generated as soon as the above modified pixels are embedded into the
original image. The secret data can be extracted by using the extracting procedure when the particular user
receives the stego-image.
2.3. The Data Hiding Scheme with High Embedding Capacity Based on General Improving EMD
Method
Observing Eq. (1) in EMD-scheme and Eq. (2) in LWC-scheme, both uses the change of weight value along
with modulus to fulfill the proper position for any point from surrounding area. Although there are outstanding
contributions on the hiding capacities in the two techniques, the parameters of embedding function are fixed
and their algorithms have to be kept. Otherwise, they will be cracked and the secret message in stego-image
will leak out. In order to improve such shortcoming, Kuo et al. [6] proposed two high capacity EMD data hiding
techniques with changing-evaluating-value, in other words, the stego-image will still be safe even though it
publishes the embedding procedure. The KWSK-scheme is summarized as following:
Step 1. Transfer the secret message s, which is 8-ary system.
Step 2. Take two adjacent pixels (X, Y) as a group.
Step 3. Compute the value of the extract function fseed with a random seed. The extract function is defined
as Eq.3:
( ) ( ) (3)8mod, bYaXYXfseed ×+×=
Where the coefficients a and b are decided by the modular table shown in Fig.1. Compute the
difference d = (s- fseed) mod 8. Adjust (X, Y) by the modular table and the seed.
FIGURE 1: The modular tables for different weights.
Similar to the LWC-scheme, the stego-image is generated when the above modified pixels are embedded into
the original image. Besides, the secret data will be extracted by using the extracting procedure when the
particular user receives this stego-image. Form the experiment simulations, the KWSK-scheme [6] still
maintains the high capacity and the image quality is almost the same as the LWC-scheme.
2.4. Least-Significant-Bit (LSB) Matching Method
In order to keep the embedding of the same amount of information as LSB matching and detect the secret
data harder than the conventional LSB matching method, Mielikainen proposed a robust LSB matching
method [5] in 2006. There are two major properties in his scheme as following:
.,),,1(),1( Znlnlfnlf ∈∀+≠−
.,),1,(),( Znlnlfnlf ∈∀+≠

Therefore, embedding message is performed for two pixels X and Y of a cover image at a time and then
adjusting one pixel of the (X, Y) to embed two secret bits message s1s2. The embedding flowchart is shown in
Fig.2 and the embedding procedure is described as following:
Step 1. If the LSB of X is the same as s1, go to step 2.
Otherwise, go to step 3.
Step 2. If the value of ( )YXf , is the same as s2, do not change any pixel. Otherwise, the value of pixel Y is
increased or decreased by 1.
Step 3. If the value of ( )YXf ,1− is the same as s2, the value of pixel X is decreased by 1. Otherwise, the
value of pixel X is increased by 1.
Where the function
( )YXf , is defined as Eq.4:
( ) (4)
2
, 





′+


 ′
=′′ Y
X
LSBYXf
Since this new LSB matching method just only increase or decrease 1 in two adjacent pixels, the difference of
the two neighborhood pixel between cover image and stego-image is very small. Hence, it can keep high
quality while hiding data.
FIGURE 2: The LSB matching embedding procedure.
3. THE PROPOSED DATA HIDING SCHEME
By using more changes of weight, a robust embedded method can be proposed, which will enhance the
security of the secret data within the stego-image[6]. Unfortunately, it needs to produce many random seeds
before the stego-image will be processed and send them to the receiver for extracting secret message from
the stego-image. How to transmit the additional information from sender to receiver is an important issue.
However, such issue does not be discussed in [6]. In order to improve the lack, we will propose an efficient
data hiding method based on the improved EMD and LSB matching methods, in which the seeds are
embedded into stego-image at the same time and the receiver can extract these seeds and secret data from
the stego-image.
3.1. The Embedding Secret Message Procedure
In our scheme, the embedding procedure is performed over three cover image pixels at a time. First, we
embed the secret message by using the improvement EMD method, and then use the following functions f1
and f2 to embed the random seeds into the stego-image.
( ) )5()(,1 YXLSBYXf +=
( ) )6()
2
(,2 Z
X
LSBZXf +



=
, where X, Y, Z are the first, second and third pixel in a group respectively. The flowchart of embedding
message is shown in Fig.3. The steps are described as follows:

Step 1. Divide the modular tables into two groups G0 and G1 shown in Fig.4.
Step 2. Take three adjacent pixels (X, Y, Z) as a group.
Step 3. Let the result of a hash function ()⋅H = 0 or 1. Compute the hash value H(x1||x2||x3||x4||x5||x6)=i and
decide to use group G0 or G1, where xi is the ith bit of pixel X. Then, we also use the random generate
to produce a seed sa
{ }3,2,1,0∈ .
FIGURE 3: The embedding secret message procedure.
FIGURE 4: The group modular tables.

Step 4. Embed the secret message into pixels (Y, Z) by using the improved EMD method.
Step 5. Transfer the seed sa to the binary stream s1s2.
Step 6. Compute v1, which is the value of f1, and check whether v1 is equal to s1 or not. If v1 is equal to s1,
then keep the original LSB of pixel X. Otherwise, we adjust the LSB of pixel X.
Step 7. Compute v2, which is the value of f2, and check whether v2 is equal to s2 or not. If v2 is equal to s2,
then keep the original Least-Second-Significant-Bit of pixel X. Otherwise, we adjust the Least-
Second-Significant-Bit of pixel X.
3.2. The Extracting Secret Message Procedure
The flowchart of extracting secret message is shown in Fig.5. There are five steps in this procedure. Now,
they are described as follows:
Step 1. Compute the value i, which is first six bits of pixel X of ()⋅H , to decide group Gi.
Step 2. Extract the first bit of random seed s1 by computing f1.
Step 3. Extract the second bit of random seed s2 by computing f2.
Step 4. Transfer the binary s1s2 to decimal value to extract seed.
Step 5. Take pixels (Y, Z) and the weight of seed in Gi to extract the secret message by computing extract
function fseed.
Therefore, the receiver can recover the secret data by using the extracting procedure.
FIGURE 5: The extracting secret message procedure.
4. EXPERIMENTAL RESULT
We perform our scheme over Lena, Pepper, Baboon and Boat, which are common pictures and shown in
Fig.6. These cover images are 512×512, 8bits and grayscale. The resultant stego-images are shown in Fig.7.
We can’t distinguish between cover-images and stego-images with human’s eyes.

FIGURE 6: Cover images.
FIGURE 7: Stego-images.
Analysis of the stego-image’s PSNR: From Tab.1, we can find out the stego-image’s quality by using our
method is lower than KWSK-scheme. In KWSK-scheme, Kuo et al. take two adjacent pixels as a group and
each pixel is at most increased or decreased by 1. In our scheme, we take three adjacent pixels at a time and
it is just only the second or third pixel to increased or decreased by 1 at most but the value of first pixel maybe
be changed by difference 3 or 1 in each pixel group. Although the stego-image’s quality in our scheme is not
good as KWSW-scheme, there is an important merit is that it does not transmit the random number seeds
before the sender and receiver communicates each other.
Analysis of embedding capacity: We take three pixels in a group to embed three bits at a time but Kuo et
al. [6] take two pixels in a group to embed three bits. Therefore, the embedding capacity of our scheme is
about 2/3 of KWSK-scheme and the experiment result shown as Table 1. Similarly, there is an important
advantage in our proposed scheme which does not need the synchronous random number seed to carry
although the embedding capacity in our scheme is less than KWSK-scheme.
KWSK-scheme[6] Our scheme
Method
Payload
(bits)
PSNR
(dB)
Payload
(bits)
PSNR
(dB)
Lena 393,216 50.175 262,143 47.164

Pepper 393,216 50.179 262,143 47.170
Baboon 393,216 50.178 262,143 47.171
Boat 393,216 50.175 262,143 47.074
TABLE 1: The comparison between KWSK-scheme and our scheme.
5. CONCLUSION
In this paper, we propose an improved scheme by using the LSB matching method to embed seeds into the
stego-image again to replace to transmit the synchronous random number seeds before the sender and the
receiver commune each other, i.e., this can improve the defect of the synchronous random number seeds in
KWSK-scheme. The experimental result shows that it can not only keep the acceptable image quality and
security but also enhance convenience for transmission in our proposed scheme.
6. ACKNOWLEDGEMENT
This work is supported by National Science Council under NSC 98-2219-E-150-001.
7. REFERENCES
[1] FOR JOURNALS: F. Cayre, C. Fontaine, and T. Furon, “Watermarking Security: Theory and Practice,”
IEEE Trans. on Signal Processing Vol.53, No.10, pp.3976-3987, Oct. 2005.
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Image Quality,” Proceedings of the 12th International Conference on MultiMedia Modelling, Bijing, China,
pp.225-232, January 2006.
[3] FOR JOURNALS: A. Ker, “Steganalysis of LSB Matching in Grayscale Images,” IEEE Signal Processing
Letters, Vol.12, No.6, pp.441- 444, June 2005.
[4] FOR JOURNALS: C. F. Lee, Y. R. Wang, and C. C. Chang, “A Steganographic Method with High
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[5] FOR JOURNALS: J. Mielikainen, “LSB Matching Revisited,” IEEE Signal Processing Letters, Vol.13, No.5,
pp.285-287, May 2006.
[6] FOR CONFERENCES: W. C. Kuo, L. C. Wuu, C. N. Shyi, and S. H. Kuo, “A Data Hiding Scheme with
High Embedding Capacity Based on General Improving Exploiting Modification Direction method”
HIS2009, Aug. 2009.
[7] FOR JOURNALS: R. Z. Wang, C. F. Lin, and J. C. Lin, “Image Hiding by Optimal LSB Substitution and
Genetic Algorithm,” Pattern Recognition, Vol.34, No.3, pp.671-683, 2001.
[8] FOR JOURNALS: H. C. Wu, N. I. Wu, C. S. Tsai, and M. S. Hwang, “Image Steganographic Scheme
Based on Pixel-Value Differencing and LSB Replacement Methods,” IEE Proceedings-Vision, Image and
Signal Processing, Vol.152, No.5, pp.611-615, October 2005.
[9] FOR JOURNALS: X. Zhang and S. Wang, “Efficient Steganographic Embedding by Exploiting Modification
Direction,” IEEE Comm. Letters, Vol.10, No.11, pp.1-3, Nov. 2006.

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