Top Banner

Click here to load reader

A new hybrid steganographic method for histogram preservation

Feb 15, 2017

ReportDownload

Engineering

ijeee

  • A new hybrid steganographic method for histogram

    preservation

    Umesh Ghanekar

    Abstract This paper presents a histogram preserving data

    embedding method for grey-scale images which is based on pixel

    value differencing (PVD) and least-significant-bit (LSB)

    substitution methods. Various PVD based steganographic

    methods achieve high data embedding capacity with minimum

    distortions in stego image at the cost of change in histogram

    characteristics which is can be detected by histogram based

    steganalysers. This persistent problem can been taken care off by

    proposed method of data hiding. The improved performance of

    the proposed method is verified through extensive simulations.

    Keywordssteganography; PVD; embedding capacity;

    histogram characteristics;

    I. INTRODUCTION

    In recent years, steganography has emerged as an

    interesting area of research. Steganography is basically used to

    enhance the communications security. It hides the very

    existence of the secret message into the cover media such as

    digital image, audio, video, text etc [1]. In this paper, grey-

    scale digital images have been used as the cover media for

    hiding the secret message.

    Many data hiding methods have been proposed so far and

    among them the most simple and well- known steganography

    method is least-significant-bit (LSB) replacement. Here, the

    secret message is concealed directly into the LSBs of each

    pixel of an image. This direct embedding procedure of various

    existing spatial domain steganographic methods like LSB

    replacement and others is incapable of exploiting the true

    embedding capacity of any cover image. An image consists of

    two areas i.e. edge area and smooth area. Edge areas can be

    embedded with more number of bits than smooth areas, as

    edges are less sensitive towards the changes in pixel

    intensities. In 2003, Wu and Tsai used this concept and

    presented a steganography method using PVD [2]. This

    method hides different amount of secret bits in consecutive

    non-overlapping pixel pairs by taking the difference value

    between the pixels of a pixel pair. Further to increase the

    embedding capacity a hybrid method based on PVD and fixed

    sized LSB method was proposed by Wu et al. [3]. In 2008,

    another hybrid method was presented based on PVD and

    modulus function [4]. This method provides higher

    imperceptibility of the stego image than the previous methods

    while maintaining good data embedding capacity. An adaptive

    LSB replacement method was also proposed in 2008 which

    utilises the basic concept of data hiding based on human visual

    system (HVS) [5]. As a result, pixels are embedded with

    different number of secret bits using LSB replacement

    method. In the year 2012, a novel adaptive data hiding method

    based on LSB substitution and PVD was proposed [6]. This

    method is able to conceal large amount of secret data and

    provide good stego image quality but is unable to preserve

    histogram characteristics.

    Here, we have proposed a steganographic method using

    LSB substitution and PVD in order to preserve the image

    histogram. In this method, we have increased the block size to

    3 3 as compared to 1 3 of adaptive LSB and PVD [6]. The central pixel of each block is termed as base pixel and 3-bits

    are embedded in this pixel with the help of LSB replacement

    method and optimal pixel adjustment process (OPAP) [7].

    Remaining pixels of the block are embedded with secret data

    bits using PVD. The performance of the proposed method is

    demonstrated through extensive simulations.

    The paper is organized as follows. Section II presents the

    proposed method. Experimental results are shown in section

    III. Finally, conclusions are given in section IV.

    II. PROPOSED METHOD

    This section deals with the procedure of proposed method which consists of three phases, namely, the range division phase, the embedding phase and the extracting phase. These phases are described as follows.

    A. Range division phase

    Prior to embedding the secret message, the grey level range [0,255] is divided into five ranges where , denotes the lower bound of the range and denotes the upper bound of the range . These five ranges can be , , , and . Fig. 1 shows the dividing case i.e. div=31 for the proposed method. It divides the range [0,255] into lower level which consist of ranges , , and higher level which include ranges , . Let are the number of bits to be embedded in the pixels falling under the range . According to HVS, changes in edge areas are less visible than smooth areas and hence more data can be

    Priya darshni,

    Dept. of Electronics and Communication Engineering National Institute of Technology

    Kurukshetra, India

    [email protected], [email protected]

    NaveenTypewritten textInt. Journal of Electrical & Electronics Engg. Vol. 2, Spl. Issue 1 (2015)e-ISSN: 1694-2310 | p-ISSN: 1694-2426

    NaveenTypewritten text139 NITTTR, Chandigarh EDIT-2015

  • embedded in edges. In the proposed method, first three ranges ( fall under the category of smooth regions whereas last two ranges falls in the edge regions. Therefore, we propose to embed bits in the lower level and bits in the higher level.

    B. Embedding phase

    The cover image is divided into consecutive non-

    overlapping blocks of size 3 3 in raster scan manner. Each block has a centre pixel named as base pixel . Data embedding in each block is performed by the following steps

    as given in [6].

    Step 1: Consider 3-rightmost LSBs of and transform these three LSBs to a decimal value, say . Read 3-bits from binary secret data in continuation and replace the 3 LSBs of

    with these binary secret data bits to obtain . Also,

    transform these bits to a decimal value, say .

    Step 2: Compute the difference value using .

    Step 3: Modify using OPAP as follows

    {

    (1)

    Step 4: Compute the absolute difference values between the

    base pixel and other pixels of the block by using

    | | (2)

    where and denotes the location of the pixel in a block. Therefore, eight difference values are calculated.

    Step 5: Assign the ranges corresponding to the differences found in Step 4 and obtain the lower bounds too i.e. .

    Accordingly, calculate which denotes the number of bits to

    be concealed into eight pixels.

    Step 6: Read bits in continuation from the binary secret

    message and transform these bit-sequences into decimal

    values, say . Now, compute the new difference values

    using

    (3)

    Step 7: Calculate the two new values of each pixel of a block

    using

    (4)

    Step 8: Choose the best new value for these pixels from the

    values obtained in Step 7 using

    {

    |

    | |

    |

    (5)

    Repeat the above procedure for every block of the cover image so as to obtain the final stego image.

    C. Extracting phase

    At first, the stego image is divided into consecutive non

    overlapping blocks of size 3 3 and then for the complete extraction of the secret message following steps are executed.

    Step 1: Select the centre pixel as the base pixel and extract 3-

    LSB bits from it. Call this binary sequence as .

    Step 2: Calculate the absolute difference values between

    the base pixel and the other pixels of a block and then find the

    range to which these difference values belong to. Then, obtain

    the lower bound of the corresponding range and also

    determine the number of bits to be extracted from each

    pixel.

    Step 3: Obtain the secret data sub-streams as by taking the

    difference between above calculated difference values and

    respective lower bounds. Transform to binary strings with

    length equivalent to .

    Finally, concatenate , to obtain the original bit sequence

    of the secret message.

    Lower-level Higher-level

    =[0,7] =[8,15] =[16,31] =[32,63] =[64,255]

    Fig.1 The dividing case (div=31) of the proposed method with lower level and higher level.

    NaveenTypewritten textInt. Journal of Electrical & Electronics Engg. Vol. 2, Spl. Issue 1 (2015)e-ISSN: 1694-2310 | p-ISSN: 1694-2426

    NaveenTypewritten textNITTTR, Chandigarh EDIT -2015 140

  • III. EXPERIMENTAL RESULTS

    The simulation is done u