AN EXTENDED VISUAL CRYPTOGRAPHY SCHEME WITHOUT PIXEL EXPANSION FOR HALFTONE IMAGES
ABSTRACT
Visual cryptography is a secret sharing scheme which uses images distributed as shares such that, when the shares are superimposed, a hidden secret image is revealed. In extended visual cryptography, the share images are constructed to contain meaningful cover images, thereby providing opportunities for integrating visual cryptography and biometric security techniques. In this paper, we propose a method for processing halftone images that improves the quality of the share images and the recovered secret image in an extended visual cryptography scheme for which the size of the share images and the recovered image is the same as for the original halftone secret image. The resulting scheme maintains the perfect security of the original extended visual cryptography approach.
Existing System
A basic 2-out-of-2 or (2; 2) visual cryptography schemeproduces 2 share images from an original image and must stack both shares to reproduce the original image. More generally,a (k; n) scheme produces n shares, but only requirescombining k shares to recover the secret image. To preservethe aspect ratio for the recovered secret image for a (2; 2)scheme each pixel in the original image can be replaced inthe share images by a 2 X 2 block of subpixels. if the original pixel is white, one of six combinationsof share pixels is randomly created. Similarly, the possibleshare combination for black pixels is also shown. Afterstacking the shares with white transparent and black opaque,the original secret image will be revealed. Stacking can beviewed as mathematically ORing, where white is equivalentto “0” and black is equivalent to “1”. Note that the resultingshare images and the recovered secret image contain 4 timesmore pixels than the original image (since each pixel of theoriginal image was mapped to four subpixels). It may also be noted that the recovered image has a degradation in visualsince a recovered white pixel is actually comprisedof 2 white and 2 black subpixels, while a black pixel is representedby 4 black subpixels in the recovered image.
Disadvantage:
Recovered image has a degradation in visualquality.
Contrast between white and black isdecreased.
Proposed System:
We propose a method for processinghalftone images that improves the quality of the share imagesand the recovered secret image in an extended visual cryptographyscheme for which the size of the share images and therecovered image is the same as for the original halftone secretimage. The resulting scheme maintains the perfect security ofthe original extended visual cryptography approach.
Advantages:
Theblock replacement approach proposed here tries to keep thelocal ratio of black to white pixels in the processed imageclose to the local ratio of black to white pixels in the original
halftone secret image. Therefore, the resulting recoveredimage is closer in quality to the original grayscale image.
ProblemStatement
When ever we transmit the data(image) in the network, any unauthenticated person can read our data(image).
In order to provide security to data(image) generally sender will encrypt the data(image) and send it the intended person and the receiver will decrypt the encrypted data(image) and uses it.
Scope:
System provides a friendly environment to deal with images. Generally tools supports only one kind of image formats. Our application supports .gif and .png (portable network graphics) formatted images and our application has been developed using core java and jsp technologies, hence provides a friendly environment to users.
VCS of an EVCS, we mean a traditional VCS that have the same access structure with the EVCS. Generally, an EVCS takes a secret image and original share images as inputs, and outputs shares that satisfy the following three option:
1)any qualified subset of shares can recover the secret image;
2)any forbidden subset of shares cannot obtain any information of the secret image other than the size of the secret image;
3)all the shares are meaningful images.
Architecture:
MODULES”
- PRE-PROCESSING HALFTONE IMAGES.
- Simple Block Replacement(SBR).
- Balanced Block Replacement.
- EXTENDED VC.
Modules Description
- PRE-PROCESSING HALFTONE IMAGES
Here, we consider the application of visual cryptographyto grayscale images by first converting the images to abinary image using a halftoning algorithm. After creating ahalftone image, in order to preserve the image size when applyingvisual cryptography and extended visual cryptography,simple methods can be applied. For example, a basic, securemethod that is easy to implement is based on a block-wiseapproach to pre-processing the binary halftone image prior toapplying visual cryptography.
- Simple Block Replacement(SBR)
TheSBR scheme considers groups of four pixels from the halftonesecret image in one 2 _ 2 block, referred as a secret block,and generates the shares block by block (rather than pixel by
pixel). As each secret block with four pixels encodes into twosecret shares each containing four pixels, the size of the reconstructedimage is the same as the original secret image afterstacking the two shares together. In this technique, all thesecret blocks in an image need to be processed before visualcryptography encoding and each secret block is replaced bythe corresponding predetermined candidate, which is a blockwith 4 white pixels (a white block) or a block with 4 blackpixels (a black block).
- Balanced Block Replacement
Thenovel aspect in this approach is to perform the block replacementsuch that there is a better balance of white and black inthe processed secret image. The previously described SBRscheme results in darker images, since blocks which containtwo white and two black pixels are converted to a black block.We shall refer to blocks of two white and two black pixels ascandidate blocks. In the BBR approach, we balance white andblack in the processed image by assigning some candidateblocks to black and others to white. Although we have discoveredthat doing the candidate block assignment randomlyto black or white improves the visual quality of the processedsecret image, even better visual results can be achieved usingan intelligent block replacement approach that considers thecharacteristics of the original image in determining whethera candidate block should be assigned to black or white. Theblock replacement approach proposed here tries to keep thelocal ratio of black to white pixels in the processed imageclose to the local ratio of black to white pixels in the originalhalftone secret image. Therefore, the resulting recoveredimage is closer in quality to the original grayscale image.
- EXTENDED VC
An extended VC scheme adds a meaningfulcover image in each share. Although image expansionis necessary to exactly preserve the information from the pixelsof the original secret image in the recovered secret image,we can use either the basic pre-processing scheme, SBR or the more advanced BBR method toensure that the share and recovered images use the same numberof pixels as the original halftone secret image. Of course,the trade-off in such an approach is a decline in image quality.
System Configuration:-
H/W System Configuration:-
Processor - Pentium –III
Speed - 1.1 Ghz
RAM - 256 MB (min)
Hard Disk - 20 GB
Floppy Drive - 1.44 MB
Key Board - Standard Windows Keyboard
Mouse - Two or Three Button Mouse
Monitor - SVGA
S/W System Configuration:-
Operating System :Windows95/98/2000/XP
Application Server : Tomcat5.0/6.X
Front End : HTML, Java, Jsp
Scripts : JavaScript.
Server side Script : Java Server Pages.
Database : Mysql
Database Connectivity : JDBC.
CONCLUSION
In this paper, we have explored extended visual cryptographywithout expansion. We have shown that using an intelligentpre-processing of halftone images based on the characteristicsof the original secret image, we are able to produce good qualityimages in the shares and the recovered image. Note thatother applications can also benefit from the pre-processing approach,such as multiple image visual cryptography, whichhides multiple images in shares.