INTERNATIONAL JOURNAL OF PROFESSIONAL ENGINEERING STUDIES Volume IV /Issue4 / JAN 2015

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COLOUR EXTENDED VISUAL CRYPTOGRAPHY USING ERROR

DIFFUSION

Aakumalla Venkata Ramana (PG Scholor)1

S. Fahimuddin P.hD2

1`D.E.C.S, Department of ECE, Annamacharya institute of technology & sciences

2Asst.Professor, D.E.C.S, Department of ECE, Annamacharya institute of technology & sciences

ABSTRACT: In this paper color visual cryptography (VC)

encrypt a color conceal data into n color halftone image

shares. Literature reviews shows that the pervious method

provides better result for only black and white or gray scale

VC only however it is not suitable for color shares due to

different color structures. Some pervious methods are not

suitable for color visual cryptography in terms of producing

either meaningful shares or meaningless shares with low

visual quality. In this paper a new technique called visual

information pixel (VIP) synchronization and error diffusion

is carried out in order to obtain meaningful color shares with

high visual quality in encryption process. It retains the

position of the pixel carrying visual information of the

original images throughout the error diffusion and color

channels generated shares pleasant to human eyes.

Comparing with the pervious method our methods provides

better performance.

Keywords: Digital half toning, error diffusion, secret

sharing, visual cryptography (VC), Color meaningful shares.

I.INTRODUCTION

Nowadays due to increases of media facilitates access, portability, efficiency and accuracy of the information presented. These undesirable effects of facile data access include an increase in opportunity for violation of copyright and tampering with or modification of content. equal probability, replacing p. where p value is replaced by the set

introduced in which data is embedded, such as copyright information, into various forms of media such as image, audio, or text with minimum amount of perceivable degradation to the “host” signal i.e., the embedded data should be inaudible and invisible to a human observer. Data hiding is generally performed by two method they are cryptography, Steganography and watermarking [3],[4],[5]. Visual cryptography (VC) is type of conceal sharing introduced by Naor and Shamir [1]. In k-out -of- n VC scheme, a secret binary image is cryptographically encoded into 푛 shares of random binary patterns. The n shares are Xeroxed and distributed amongst n participants. One for each participant and no participant knows the information of the other participant. By superimposing and transparencies together any k or more participant can reveal the secret image. The secret cannot be decoded by any 푘 − 1 participant, even if infinite computational power is available to them. VC scheme is presented by NAOR and Shamir [1] serves a basic model and has been applied to many applications.

Figure 1 Construction of (2,2) VC scheme: a secret pixel is encoded into four sub pixels in each of two shares. The decryption pixel is obtained by superimposing the block in shares one and two. Consider a simple (2-2)-VC scheme to understand the VC scheme .In Figure 1 Each pixel p from a secret binary image is encoded to m black and white sub pixel. If p is a white (black), one of the six columns is selected randomly with

INTERNATIONAL JOURNAL OF PROFESSIONAL ENGINEERING STUDIES Volume IV /Issue4 / JAN 2015

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of the four sub pixels two of them white and two black. Sub pixel provides the clue for the original pixel value p. On other hand in decryption process sub pixel having four black p pixel indicates that the sub pixel comes from the black pixel p Figure 2 exhibits an example of a simple (2,2)-VC scheme with set of sub pixel shown in Figure.1.Figure.2(a) shows the conceal binary message,Figure.2(b) and (c) shows that the encrypted shares for two participants. Figure 2(d) show the output of the secret message. The decoded image is clearly identified and it has some contrast loss. Blundo [8] presented an optimal contrast k-out-of-n scheme for the contrast loss problem in the reconstructed images. Ateniese [2] presented a general method for VC scheme based upon the general access structure. The VC scheme is extended to gray scale share images rather than binary images shares [9]-[12]. Huo [13] converted grayscale image into halftone images and binary VC scheme to generated grayscale shares. Ateniese [14] developed a method to extended visual cryptography (EVC) in which shares contain not only the conceal data but also meaningful binary shares. Wang [15] generalized the Ateniese’s scheme using concatenation of basis matrices and the extended. Zhou et al. [17] halftoning method to produce good quality halftone shares in VC. FU [4] generates halftone shares that carry visual information by using VC and watermarking methods. Myodo [18] presented a method to generated meaningful halftone image using threshold arrays. Halftone shares shows the meaningful images presented in the Wang et,al [32] using error diffusion techniques. This paper provides simple and efficient color VC encryption method which leads the meaningful shares. It provides two fundamental principle used in the generation of shares, error diffusion and VIP synchronization. Error diffusion is simple and efficient algorithm for image halftone generation. In VIPs synchronization color channels improves visual contrast of shares. Color of the encrypted pixels and the contrast can be reduced due to the random matrix permutation. Random matrix permutation is key security features. In gray scale visual method it does not affect the quality but in color scheme, execution is independent of the random matrix permutation for each color channel. It causes the color distortion by placing the VIPs at random position in sub pixel which finally reduces the image quality. With matrix permutation the color and contrast is prevented in VIP synchronization.

INTERNATIONAL JOURNAL OF PROFESSIONAL ENGINEERING STUDIES Volume IV /Issue4 / JAN 2015

IJPRES

INTERNATIONAL JOURNAL OF PROFESSIONAL ENGINEERING STUDIES Volume IV /Issue4 / JAN 2015

IJPRES

the position (푝 ,푞 ) and each sub pixel takes one of the corresponding color channels of the message pixel. Algorithm 2. Produces n encryption shares 푋 Example of the matrices distribution for (2, 2) color EVC method is depicted in Figure.2. Figure.2 (a) shows the matrices distribution along with each message pixel. Each binary bit on three color channels of message pixels is expanded into four sub pixels on corresponding color channels throughout the n encryption shares by taking the matrices 푆 or 푆 according to the bit value. Figure.2 (b) depicts a decryption mechanism by the unit of sub pixel showing how they present the desired color of the original message pixel. Since the matrices 푆 and 푆 are derived in a way that the contrast difference is 훼, the decrypted sub pixel shows the intended color of the message pixel with probability훼.

region and its performance near edges or in area of high

Figure.3(a) Block diagram of error diffusion with share encryption. If 푆 (푚, 푛) is a VIP 푔 (푚,푛) is determined by the output of the thresholding quantization otherwise 푔 (푚,푛)

C. Share generation via Error diffusion The distribution of the basis matrices is completed; a half toning algorithm is applied to produce the final encrypted shares. In our method error diffusion is simple and efficient. Figure 5(a) shows a binary error diffusion diagram designed for our method. To produce the ith halftone share, each of the three color layer are fed into the input. The process of generating halftone via error diffusion is similar to that as shown in the Figure.3 expects that 푓 (푚, 푛)is the (푚,푛)th pixel on the input channel 푗(1 ≤ 푖 ≤ 푛, 1 ≤ 푗 ≤ 3) of the ith share. Difference between our method and standard error diffusion is that the message information components, non 푐 are predefined on the input shares such that they modified during the halftone process. The red VIPs that are already defined by the error diffusion the 푐 are also VIPs whose values are to be decided by refering the corresponding pixel values of original images and error from neighboring pixels when the error filter window comes. The non 푐 elements may increases quantization errors added to the shares, but in turn, these errors are diffused away to neighboring pixels. The visual quality of shares via error diffusion is improved through edge enhancement methods [27]. The measure of the particular half toning algorithm is its performance in DC

INTERNATIONAL JOURNAL OF PROFESSIONAL ENGINEERING STUDIES Volume IV /Issue4 / JAN 2015

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frequency image content can be manipulated through pre-filtering the image prior to half toning. So edges sharpening filter prior to half toning such that

Where 푋[푛] stands for the original image,휓[푛] is the digital Laplacian filter, * denotes convolution and 훽 is a scalar constant (훽 > 0) regulating the amount of sharpning with β leading to a sharper image 푋 , The efficitveness of the color diffusion can be obtained. in the simulation result

III.EXPERIMANTAL RESULTS

Figure 4: Result Analysis

a)Secret Image

b)cover image1

c)cover image2

d)cover image3 e)cover image4

f)Received image1

g)Received image2

h)Received image3

i)Received image4 j)Extracted image

For conducting experiment we have considered four cover images and a secret image which is to be shared among the four images. Figure 4 shows the different images used and the step wise result obtained with the proposed algorithm. As we can see the scheme proposed generates high quality of meaningful color shares as well as the colorful decrypted share using VIP synchronization and error diffusion methods. The VIPs are pixels that carry pixel values of original images to make shares meaningful.

V.CONCLUSION

In this paper encryption method is developed to construct color EVC scheme with VIP synchronization and error diffusion for visual quality is improved. In VIPs synchronization the position of pixel that carries visual information of original images across the color channels. It retains the original pixel values before and after the encryption. Error diffusion is used to develop the shares such that the noise introduced by the preset pixels is diffused away to neighbors. Tradeoff between contrast of encryption and decryption shares is recognized with the color conceal message having low contrast. VIP synchronization or error diffusion can be broadly used in much VC method for color images.

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