Modified weighted embedding method for image steganography

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Modified weighted embedding method for image steganography

  1. 1. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 3, May – June (2013), © IAEME 154 MODIFIED WEIGHTED EMBEDDING METHOD FOR IMAGE STEGANOGRAPHY #1 Geetha C.R. #2 Dr.Puttamadappa C. Research scholar, Professor and principal, Jain University Sapthagiri College of Engineering, Bangalore, Karnataka, INDIA Bangalore, Karnataka, INDIA ABSTRACT In this paper, proposing a unique steganography method for the digital images. In steganography embedding the data inside an image before transmitting it for secure communication. The basic method used in time domain for image steganography is LSB substitution which can easily be detected. Hence instead of simple LSB substitution here choosing an embedding algorithm which uses the decimal value of the data to be hidden. This makes the data to be hidden as the key itself. With this method high security along with good visual quality is obtained. Keywords: Security, Cryptography, Multiple edge detection, Minimum error replacement, Variable embedding ratio. I. INTRODUCTION Present communication system uses digital signals more than analog signals. Digital communication system uses digital signals, which are sent through the communication channel. Communication channels are susceptible for the intrusions. Internet is the major channel for communication and is very much necessary to secure the data transmitted through the internet. Many methods are developed to secure data. Data security is the major area where many developments are required. Cryptography is used extensively to secure the data. Steganography is another method which can be used to secure the data. Cryptography modifies the data with respect to some fixed model, so that the information is scrambled. But in Steganography a cover image is taken and the data is embedded into it in such a way that cover image is least altered. So in Steganography, not only the information is hidden also the existence of the information is hidden. It may be some time is required to hide the presence of INTERNATIONAL JOURNAL OF ELECTRONICS AND COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET) ISSN 0976 – 6464(Print) ISSN 0976 – 6472(Online) Volume 4, Issue 3, May – June, 2013, pp. 154-161 © IAEME: www.iaeme.com/ijecet.asp Journal Impact Factor (2013): 5.8896 (Calculated by GISI) www.jifactor.com IJECET © I A E M E
  2. 2. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 3, May – June (2013), © IAEME 155 secrete data rather than just making the data encrypted. Steganography is hence used to make the data more secure and then its existence is made secrete as well. It’s better to use a digital image for Steganography. Digital images can store large amount of data. For example let us take an example of 512×512 grayscale image will have 262,144 pixels and each pixel is made up of 8-bits. So the total numbers of bits in the image is 2,097,152. The total number of LSB bits in the image is 262,144. If we embed only for LSB bits in the image we can still hide 262,144 bits of data. This makes digital images suitable for Steganography. Also digital image is a common data which is shared in the internet and that makes image steganography better than any other. The simplest way for image steganography is LSB substitution method. In LSB substitution method the information which is to be hidden is converted into bit stream. The LSB bits of each pixel of the image is then substituted or replaced by the information bits. Chan C.K and Chen L.M [1] proposed simple LSB substitution method. Simple LSB substitution method is simple but it is not secure. Simply by extracting the LSB bits we can get the information back. Wang R.Z, Lin C.F and Lin J.C [2] proposed moderately significant –bit replacement method. Marghny Mohamed, Fadwa Al-Afari, and Mohammed Bamatraf [3] proposed LSB substitution by genetical-optical key permutation. Neighbor pixel information method is another way in which the number bits substituted for a given pixel is dependent on its neighbor pixel values. MoazzamHossain, SadiaAl Haque, FarhanaSharmin [4] proposed steganography method using neighborhood pixel information. But the PSNR is obtained was about 43.144dB. For the less amount of data hidden a PSNR of 43.144 dB was less. Other methods include Edge detection which along with Variable embedding can be used to increase the amount of data hidden by a large margin but the PSNR dropped drastically which went against the definition of steganography. Hence in this paper we propose the Value Weighted embedding method which clearly retains high visual quality as the cover image with little compromise in the amount of data embedded. This method can also be combined with many error reducing methods such as MER and AER to further increase visual quality. II. PROPOSED METHOD In this method while embedding the data the decimal value of the data is considered. The data to be embedded is first converted into decimal values, then these decimal values are used to embed the data. Here instead of directing replacing the LSB with the data bits we use the magnitude of the input data to just compliment certain LSB. The exact process of embedding is given in Fig.1 A. Embedding Algorithm a) Let the data to be embedded be in the form of bit stream 'X'. X= [X13 X12 X11 X10 X9 X8 X7 X6 X5 X4 X3 X2 X1 X0] where, X0 to X13 take values 0 or 1. Example:- X= [00000110010101000111100101...]
  3. 3. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 3, May – June (2013), © IAEME 156 b) Next convert this input bit stream into a form of 1D array of 3 digits decimal numbers 'Y'. Hence divide the input bit stream into groups of 13 bits and convert Fig.1: Block diagram for Data Embedding them into decimal by multiplying in powers of 2. This step can be avoided if the input is characters by considering their ASCII values. This step can be avoided if the input is characters by considering their ASCII values. Y= [ X8*28 + X7*27 + X6*26 + X5*25 + X4*24 + X3*23 + X2*22 + X1*21 + X0*20 ] Example: Y = [0405, 0485..] c) Consider the original image called the cover image. Find the edges. Now divide the array of edges into 1x5 blocks and consider these blocks as 1D arrays of pixels with 5 elements each. d) Now consider the first decimal data to be embedded, divide that number into 3 digits according to their position weight i.e. 1000th , 100th,10th and units place. Each digit is embedded separately depending upon their position value and decimal value. Example Z = [0 ,4 , 0, 5 ] e) Now move to the next decimal value and the next image block and repeat the steps d) and e) till all the data is
  4. 4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 3, May – June (2013), © IAEME 157 Let First Image block = [ 100, 105, 103, 102, 100 ] Digits to be embedded Z = [ 0, 4, 0, 5 ] f) Now move to the next decimal value and the next image block and repeat the steps d) and e) till all the data is embedded or the entire image is used. The image obtained at the end is called the Stego image. g) The above table given here is the normal order without any randomness. But this order can changed like the LSB complimented for unit and tenth places can be interchanged. This increases security and these tables act as the key for the embedding and retrieval process. Ref. Fig.3 Table 1: Change of Pixel as per Digits Value Digits Value Pixels to be Changed in 1x5 Matrix 0 None 1 First 2 Second 3 Third 4 Fourth 5 Fifth 6 First and Fifth 7 Second and Fifth 8 Third and Fifth 9 Fourth and Fifth The above table given here is the normal order without any randomness. But this order can changed like the LSB complimented for unit and tenth places can be interchanged. This increases security and these tables act as the key for the embedding and retrieval process. Table 2: Key for Embedding Digits Position LSB to be Complimented Unit Last LSB Tenth 2nd Last LSB Hundredth 3rd Last LSB Thousand 4th Last LSB
  5. 5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 3, May – June (2013), © IAEME 158 Fig.2: Retrieval block diagram Experiments are carried out to support our theory and the following results are found. Experiments are done in MATLAB 2011a version. Experiment is carried out on different grayscale images and a comparative study is presented. B. Retrieval Retrieval is actually easier; the receiver first subtracts the cover image and the stego image. Then uses absolute function on the difference to convert all 1's and -1's to 1's. Again divides the image into many 1 x 5 blocks. Then using the key i.e. the embedding table the retriever obtains the original data. a) Edge detection is first applied on an untouched cover image present in the database and its edges are detected. b) These pixels are stored in the form of 1D array for both the cover image and also the absolute function on it. This is done to detect the pixels whose value is changed and also make sure that the array has no negative values. Stegoimage, hence there are now two 1D arrays of pixels. c) Another array is formed by subtracting these both the arrays an applying absolute d) The array is divided into 1x5 blocks again, then with the help of the value present in the array and the key i.e. the table the data is extracted
  6. 6. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 3, May – June (2013), © IAEME 159 Table 3: Methods proposed by MoazzomHosain, Sadia Al Haque and FarhanaSharmin Fig.3: Embedding Method III. EXPERIMENTAL ANALYSIS Table 4: Value weighted embedding method for whole image Bits Hidden PSNR in dB 262144 (1 Bpp) 43.21 470025(Max) 40.65 Method Maximum Hiding Capacity(In Bits) PSNR(In dB) Four Neighbors 392208 41.1468 Diagonal Neighbors 395680 40.6505
  7. 7. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 3, May – June (2013), © IAEME 160 Fig.4: Baboon a)Original b)Stego Table 5: Value weighted embedding only in edge pixels Image Bits Hidden PSNR in dB Lena 96785 42.6446 Baboon 155220 40.2119 Peppers 84708 42.8209 By observing the two tables 4 and 5 it can seen that in our method not only the hiding capacity has increased but also the visual quality is high compare to the Four neighbors and Diagonal neighbors method. IV CONCLUSION With this method the security increases significantly with little distortion of the visual quality, also the data hiding capacity is good. For future work the visual quality can be improved by employing some error reducing techniques such as MER. Fig.5: Lena a)Original b)Stego
  8. 8. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 3, May – June (2013), © IAEME 161 REFERENCES [1] Chan K. and Cheng M. “Hiding Data in Images using Simple LSB Substitution” Computer Journal of Pattern Recognition Letters, volume 37,No.3, PP . 469-474, 2004. [2] Wang R. Z , Lin C. F and Lin J. C “Hiding Data in Images Optimal Moderately Significant –bit replacement”, IEE Electron Letter, vol. 36, no. 25, PP. 2069-2070, 2000. [3] Marghny Mohamed, Fadwa Al-Afari, and Mohammed. Bamatrf “Data Hiding by LSB substitution using Genetic Optimal Key Permutation”, International Arab Journal of e-technology, vol 2, No.1 January 2011. [4] MoazzamHossain, Sadia Al Haque, FarhanaSharmin. “Variable Rate Steganography International Arab Journal of information technology, vol. 7, No. 1, January 2010. [5] Li Li, Bin Luo, and Qiang Li Xiaojun Fang., “A color Images steganography method by multiple embedding strategy based on Sobel operator conference on multimedia information networking. [6] Sonali Patil, Kapil Tajane and Janhavi Sirdeshpande, “Analysing Secure Image Secret Sharing Schemes Based on Steganography”, International Journal of Computer Engineering & Technology (IJCET), Volume 4, Issue 2, 2013, pp. 172 - 178, ISSN Print: 0976 – 6367, ISSN Online: 0976 – 6375. [7] Vismita Nagrale, Ganesh Zambre and Aamir Agwani, “Image Stegano-Cryptography Based on LSB Insertion & Symmetric Key Encryption”, International Journal of Electronics and Communication Engineering & Technology (IJECET), Volume 2, Issue 1, 2011, pp. 35 - 42, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472.

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