Query: Visual Cryptography

title: Improving the Visual Quality of Size Invariant Visual Cryptography for Grayscale Images: An Analysis by Synthesis (AbS) Approach
abstract: In visual cryptography (VC) for grayscale image, size reduction leads to bad perceptual quality to the reconstructed secret image. To improve the quality, the current efforts are limited to the design of VC algorithm for binary image, and measuring the quality with metrics that are not directly related to how the human visual system perceives halftone images. We propose an analysis by synthesis (AbS) framework to integrate the halftoning process and the VC encoding: the secret pixel/block is reconstructed from the shares in the encoder and the error between the reconstructed secret and the original secret images is fed back and compensated concurrently by the error diffusion process. In doing so, the error between the reconstructed secret and original secret is pushed to high frequency band, thus producing visually pleasing reconstructed secret image. This framework is simple and flexible in that it can be combined with many existing size invariant VC algorithms, including probabilistic VC, random grid VC, and vector/block VC. More importantly, it is proved that this AbS framework is as secure as the traditional VC algorithms. Experimental results demonstrate the effectiveness of the proposed AbS framework.

title: A highly robust and secure image watermarking based on classification and visual cryptography
abstract: In this paper a new robust image watermarking algorithm based on blocks classification and visual cryptography (VC) is presented. First the original image is decomposed into non overlapping blocks. Then, we use canny edge detection and the support vector machine (SVM) classification method to categorize these blocks into smooth and non smooth classes. The VC technique is used to generate two image shares: A master share that is constructed according to the block classification results and an owner share generated by using the master share together with a binary watermark. To verify the ownership of the image, the watermark can be retrieved by stacking the master share and the owner share. By skipping blocks which are not robust against attacks, the robustness of our proposed watermarking method is significantly improved. Our method is completely imperceptible because the watermark pattern is concealed without modifying the original host image.

title: A combination of color black and white visual cryptography and polynomial based secret image sharing
abstract: A new k n threshold secret image sharing scheme with two decoding options is introduced in this paper. The proposed scheme combines color black and white visual cryptography scheme (CBW VCS) and polynomial based secret image sharing (PSIS) together, to offer stacking to see decryption and lossless image reconstruction. To construct the color shares, a general k n threshold CBW VCS is firstly given. A grayscale secret image is converted to a p radix image and a binary image. The p radix image is encrypted by the k n PSIS under mod p operation, and n p radix shadows are obtained. Then, a color share generation algorithm with data embedding is proposed to construct n color shares. Theoretical analysis and sufficient experiments are provided to show the effectiveness and advantages of the proposed scheme.

title: k Out of n Region Based Progressive Visual Cryptography
abstract: Recently, multiple $k, n$ region incrementing VCSs (RIVCSs) have been proposed that can gradually reconstruct secrets in a single image. In $k, n$ RIVCS, the secret image is subdivided into multiple regions in such a way that any $t$ shadow images, where $k \le t \le n$ can be used to reveal the secret in the $t k+1$ )th region. This region incrementing property provides progressive decoding. However, the regions in previous RIVCSs are disjointed: no two regions have overlapping areas. In this paper, we discuss a $k, n$ region in region progressive VCS (RPVCS) Our $k, n$ RPVCS has $n k+1$ secrecy level regions, and each region can be located within any previous region. This new type of region allocation not only provides more areas in which to hide the secret compared with the non overlapping regions in RIVCS but also provides different presentation methods in progressive decoding.

title: Secure telemedicine using RONI halftoned visual cryptography without pixel expansion
abstract: To provide quality healthcare services worldwide telemedicine is a well known technique. It delivers healthcare services remotely. For the diagnosis of disease and prescription by the doctor, lots of information is needed to be shared over public and private channels. Medical information like MRI, X Ray, CT scan etc. contains very personal information and needs to be secured. Security like confidentiality, privacy, and integrity of medical data is still a challenge. It is observed that the existing security techniques like digital watermarking, encryption are not efficient for real time use. This paper investigates the problem and provides the solution of security considering major aspects, using Visual Cryptography (VC) The proposed algorithm creates shares for parts of the image which does not have relevant information. All the information which contains data related to the disease is supposed to be relevant and is marked as the region of interest (ROI) The integrity of the image is maintained by inserting some information in the region of non interest (RONI) All the shares generated are transmitted over different channels and embedded information is decrypted by overlapping (in XOR fashion) shares in th(1) time. Visual perception of all the results discussed in this article is very clear. The proposed algorithm has performance metrics as PSNR (peak signal to noise ratio) SSIM (structure similarity matrix) and Accuracy having values 22.9452, 0.9701, and 99.8740 respectively.

title: Generalized visual cryptography scheme with completely random shares
abstract: A modification of the standard Naor Shamir scheme for visual cryptography and visual secret sharing is proposed. Better statistical properties of shares are obtained at the cost of the slightly worse quality of reconstructed images. Advantages and disadvantages of such an approach are discussed.

title: Efficient constructions for progressive visual cryptography with meaningful shares
abstract: In a progressive visual cryptography scheme (PVCS) the clarity of recovered images can be enhanced by increasing the number of stacking shares. Noise like shares are hard to identify, therefore, user friendly progressive visual cryptography schemes (FPVCSs) generate meaningful shares. This paper proposes two encryption approaches to construct FPVCSs. One is a general OR based FPVCS called (2, n) FPVCS, and the other is an XOR based FPVCS called (2, n) XFPVCS. The common issues of the two models include: (1) systematic approaches, (2) avoiding the pixel expansion, (3) providing adjustable visual quality of meaningful shares, and (4) eliminating residual traces of cover images. Moreover, the paper theoretically analyzes and carries out experiments to verify the visual qualities of the proposed two models. The experiment results indicate that the proposed approaches can accomplish these objectives simultaneously. In addition, (2, n) FPVCS can adjust the threshold of trace elimination by setting a parameter, which improves the flexibility of the proposed approach. As well as (2, n) XFPVCS obtains a fully decrypted final recovered image.

title: A stegano visual cryptography technique for multimedia security
abstract: Owing to the increasing growth in digital communication as well as the multimedia applications, security has now become a very significant problem in the communication as well as storage space of such images. The Visual Cryptography (VC) has been used for hiding the information that are in the images which is a special technique of encryption that is decrypted by a human visual system. In this paper, a technique for embedding a secret message within that of a cover image to ensure the interceptors will not observe the presence of such hidden data is presented. The method has an essential conception by means of a simple Least Significant Bit (LSB) substitution. Being inspired by the steganography approach, the current work splits the cover images into n blocks of 8X 8 pixels and into a secret message of n partitions in order to improve the image quality and to increase the capacity of secret message along with its security level. For the purpose of improving this stego image quality and for increasing the capacity of secret message along with its security level, being inspired by the current work that splits cover images into the n blocks of 8X 8 pixels and into a secret message of n partitions. In the proposed method, the Cuckoo Search (CS) is used for searching an approximate and optimal solution of finding any optimal substitution matrix to transform the message in every block as opposed to finding a single optimal matrix for substitution and the entire cover image is presented. The final quality of its resulting in the stego image, and its secret message and its capacity with the level of security of this method proposed will be calculated and then comparted to the other different methods. The results of the experiment proved that the proposed method outperformed all the Joint Photographic Experts Group (the JPEG) and the Joint Quantization Table Modification (the JQTM) based method in terms of quality of image, security level and embedding capacity.

title: Collaborative Visual Cryptography Schemes
abstract: A <inline formula> <tex math notation="LaTeX"$k,n$ /tex math>/inline formula> conventional visual cryptography (VC) scheme is designed to share one secret and each participant takes one share. When some common participants are involved in multiple VC schemes for multiple secrets, each needs to take multiple shares. This procedure needs more shares, which is inconvenient. It is desirable that the collaboration between the VC schemes can allow each common participant to keep only one share. Simply merging or gluing together two traditional <inline formula> <tex math notation="LaTeX"$k_{1} /tex math>/inline formula> <inline formula> <tex math notation="LaTeX"$n_{1} /tex math>/inline formula> and <inline formula> <tex math notation="LaTeX"$k_{2} /tex math>/inline formula> <inline formula> <tex math notation="LaTeX"$n_{2} /tex math>/inline formula> VC schemes, after making their pixel expansions the same, might be able to facilitate the collaboration and allow each common participant to keep only one share. But there is a security risk that when a subset of <inline formula> <tex math notation="LaTeX"$k_{1} /tex math>/inline formula> participants are from the collection of noncommon participants, some from scheme 1 and some from scheme 2, they can reconstruct secret 1, which is inconsistent with the intention of the original scheme. Similarly, <inline formula> <tex math notation="LaTeX"$k_{2} /tex math>/inline formula> noncommon participants could reconstruct secret 2. This shortcoming is inherited from the brute force combination of traditional schemes. Therefore, a more sophisticated mechanism is required; this is the main task of this paper. In this paper, we first transform collaborative VC (CVC) schemes into the multiple secrets VC scheme with a general access structure. The construction of the basis matrices in CVC scheme between two VC schemes is formulated into an integer linear programming problem that minimizes the pixel expansion under the corresponding security and contrast constraints. Also the collaboration among more VC schemes is constructed. Finally, the experimental results illustrate the construction procedure of the CVC scheme and demonstrate the effectiveness of the CVC scheme.

title: Extended visual cryptography techniques for true color images
abstract: In this work, two extended visual cryptography techniques for sharing color images are proposed. Three meaningful shares are generated in both techniques using a block size of 5 x 5 corresponding to each pixel of original secret image. First proposed technique is (3, 3) EVCT in which first share contains R component, second contains G component and third contains B component of the secret image. All three shares are required to reconstruct the original secret image on the receiver side. Second technique is (2, 3) EVCT in which any 2 out of 3 shares are needed to recover the original secret image on the receiver side. Out of these shares, first share contains the RG components, second contains GB components and third contains RB components of the secret image. All shares in both techniques are meaningful as they contain the cover images along with the information of the original secret image. These shares are made meaningful in order to increase the security and to avoid the suspicion that something is hidden there. The proposed techniques are lossless in nature and are less complex. The dimensions of the original secret image, cover images, regenerated secret image are same. The effectiveness of the proposed techniques have been shown by comparing their results with the results of the existing techniques on the basis of various parameters.