Size-Invariant Visual Cryptography With Improved Perceptual Quality for Grayscale Image

The reconstructed image of probabilistic visual cryptography (VC) is inevitably accompanied by the loss of secret image information and degradation of visual quality. Since halftone technique can realistically simulate grayscale continuous tone image with a binary image, in this paper, by combining VC sharing with grayscale image halftone technique, we propose a probabilistic VC scheme for grayscale image using EDBS (Efficient Direct Binary Search) to improve the quality of the reconstructed image. The probabilistic VC sharing is adopted into the EDBS halftone process, and the reconstructed image is taken as the optimization object. Through local optimizations and global iterations, the optimal reconstructed image is finally achieved under the established optimization strategy. Theoretically the proposed scheme possesses the same security strength as the traditional VC and experimentally the comparative analysis verifies the effectiveness of this scheme.

We introduce a process for optically reconstructing full-color holographic images recorded by optical scanning holography. A complex RGB-color hologram was recorded and converted into a binary hologram using a direct binary search (DBS) algorithm. The generated binary hologram was then optically reconstructed using a spatial light modulator. The discrepancies between the reconstructed object sizes and colors due to chromatic aberration were corrected by adjusting the reconstruction parameters in the DBS algorithm. To the best of our knowledge, this represents the first optical reconstruction of a full-color hologram recorded by optical scanning holography.

Related to the growth of data sharing on the Internet and the wide - spread use of digital media, multimedia security and copyright protection have become of broad interest. Visual cryptography () is a method of sharing a secret image between a group of participants, where certain groups of participants are defined as qualified and may combine their share of the image to obtain the original, and certain other groups are defined as prohibited, and even if they combine knowledge of their parts, they can’t obtain any information on the secret image. The visual cryptography is one of the techniques which used to transmit the secrete image under the cover picture. Human vision systems are connected to visual cryptography. The black and white image was originally used as a hidden image. In order to achieve the owner’s copy right security based on visual cryptography, a watermarking algorithm is presented. We suggest an approach in this paper to hide multiple images in video by meaningful shares using one binary share. With a common share, which we refer to as a smart key, we can decrypt several images simultaneously. Depending on a given share, the smart key decrypts several hidden images. The smart key is printed on transparency and the shares are involved in video and decryption is performed by physically superimposing the transparency on the video. Using binary, grayscale, and color images, we test the proposed method.

Visual cryptography was firstly proposed by Naor and Shamir in 1994, which has been extended into many applications, including image encryption, information hiding, visual authentication, and visual identification. One important security issue in visual cryptography is the cheating prevention. However, in 2006, Horng et al. introduced the cheating problem in visual cryptography, where some dishonest participants, cheaters, can deceive other participants, victims, using forged transparencies. Since that, many cheating prevention works have been done in this area. In this paper, we introduce a new cheating prevention scheme which is secure and more efficient than previous schemes.

Security has become an important issue as information technology has become increasingly pervasive in our everyday lives. Security risks arise with a display that shows decrypted information. In this paper, we propose a secure information display technique using visual cryptography. Its decryption requires no special computing devices and is implemented using only human vision: the proposed display appears as a random pattern to anyone who looks at it unless the person views the displayed image through a decoding mask. We have constructed code sets to represent grayscale and multicolored images. Each pixel in a secret image is expanded to a group of subpixels. The displayed image consists of black and white subpixels to encrypt a grayscale image. To encrypt a multicolor image, black, red, green, and blue subpixels compose the displayed image. The decoding mask consists of transparent and opaque subpixels. Every pixel is encrypted using a pair that is chosen at random. We have demonstrated the proposed secure display with an LCD panel and a transparency on which a decoding mask was printed. The secret image was visible for a viewer within the viewing zone, although viewers outside the viewing zone perceived it as a random dot pattern.

Spatial Light Modulators currently available lack of resolution to display large hologram, it is then necessary to find some technique to broaden the size of the reconstructed image. For example, time multiplexing can be use to tile several elementary holograms via a high speed scanning system. However, the best compromise to exploit the bandwidth of the SLM is to use binary data, holograms acquired from real objects must therefore be converted from gray scale to a binary format. The Direct Binary Search algorithm (DBS) is a method that has been developed to generate binary holograms, but the resulting holograms can reconstruct the objects only in a 2D plane. We propose to adapt the DBS algorithm to reconstruct holograms instead of directly reconstructing the image, our proposed method preserve therefore 3D information.

Security has gained a lot of importance with the rapid development of communication/storage technology. Protecting the data has become an important issue. In this paper a transmission system with enhanced security is proposed for the image information. Here, the secret image is encrypted and transmitted by using a combined technique that make use of Discrete Wavelet Transform (DWT), Visual Cryptography (VC) and Water marking. DWT is first used for the compression of the secret image. Visual cryptography encodes the compressed image into noise like shadow images known as shares. Shares are made invisible by digital watermarking, which provides additional security. By stacking the shares together, the secret image can be visually decoded. Different image types are used to evaluate the performance of the proposed scheme. Comparison with different values of scaling parameter M, which is used to decrease the size of image in the VC is also done. The results clearly indicate that the proposed scheme can send more data with less bandwidth more secretly.

By splitting a picture into many parts, which, when reassembled, disclose the original image without requiring complicated math, visual cryptography is a strong method for protecting visual information. Problems with pixel enlargement, decreased picture quality, and restricted access structures are common with traditional visual cryptography techniques. Our proposed improved visual cryptography approach incorporates pixel-wise operations and critical access structures to solve these challenges and increase flexibility, picture quality, and security. To reconstruct a picture, our technique calls for building visual cryptographic shares based on critical access structures that specify the exact combinations of shares needed. In order to maintain the image's resolution and reduce pixel expansion, we use pixel-wise processes. By improving the peak signal-to-noise ratio (PSNR) by up to 20% compared to conventional approaches, experimental data show that our strategy greatly improves picture quality. In addition, the suggested approach guarantees that individual shares do not disclose any information on the original picture, thereby maintaining high security requirements. Finally, it is clear that the enhanced visual cryptographic system is well-suited for a wide range of uses in safe communications and data security due to its strong solution for secure picture sharing, increased picture quality, and adjustable access control.

Visual Cryptography is a secret sharing scheme which owns the technique of sharing the visual information like pictures, text etc. It encrypts a secret into n visual shares printed in transparencies and shared among n participants. Qualified subsets of participants superimpose their transparencies to reconstruct the actual visual secret. The decryption of the visual secret demands no complex computation as the image can be retrieved by the human visual system after superimposing. This paper proposes a tagged visual cryptography for color images, where the secret image is splitted into two base shares based on the traditional visual cryptography scheme. The generated base shares are stamped with the tag pattern using the probabilistic visual cryptography scheme to obtain the tagged shares. One of the main advantage of using tag patterns is providing the participants with augmented information to identify the relevant shares among the numerous shares. During reconstruction the tag patterns are obtained by folding up the individual tagged shares. Superimposing the shares results in the secret color image which retains its original size thus ensuring no pixel expansion.

This letter presents a method for implementing visual cryptography (VC) in which an additional tag is attached to each generated share. The proposed (t, n), 2 ≤ t ≤ n tagged visual cryptography (TVC) scheme works like a traditional VC scheme does, where the original image is encoded in n shares in such a way that the secret can be revealed by superimposing any t or more shares, but knowledge of less than t shares gets no secret information. A notable characteristic of TVC is that an extra tag can be revealed by folding up each share, which provides users with supplementary information such as augmented message or distinguishable patterns to identify the shares. The tagging property can easily be applied to any reported VC scheme to endow the generated shares with more capabilities. Construction methods and simulation results of the proposed (t , n) TVC based on conventional matrix-based VC and probabilistic-VC are illustrated in the letter.

Just noticeable difference (JND) reflecting visual redundancy of human visual system (HVS) has been widely adopted in image/video processing. In this work, we introduce a novel JND model in pixel domain for screen content (SC) images. Due to the obvious different impacts on HVS between pictorial region and computer-generated texture, we decompose a SC image into screen content set (SCS) and non-screen content set (non-SCS) for JND modeling. For SCS, edge masking effect is mainly considered by using a parametric model with an adaptive edge representation. For non-SCS, both the edge masking effect and pattern masking effect are taken into account to improve distortion tolerance by injecting more noise to pattern complexity region without perceptual quality degradation. Furthermore, visual saliency is employed to adjust pattern masking effect in the view of HVS. Experimental results show that compared with state-of-the-arts, the proposed JND model can tolerate more distortion, and provide better perceptual quality at the same noise level.

This paper presents a video halftoning for electronic papers. Based on the direct binary search (DBS) algorithm, the video frames are halftoned in order. The proposed approach tends to minimize the flickers on the stationary regions by referring to the previous frame and processing the pixels in pseudo random ordering. The main feature of the proposed approach is that the frame can be gotten with an acceptable result in one iteration. The experimental results show the proposed approach significantly improves the video quality compared with the error diffusion based and the original DBS.

We propose a new multicriteria method for the determination of computer-generated holograms (CGH's). For this purpose, the direct binary search (DBS) algorithm for computing CGH's has been modified to converge on a new error function that defines the optimal trade-off among different criteria. This approach allows us to control the trade-off between the amplitude error and the diffraction efficiency and to provide a rigorous figure of merit. Comparisons among different encoding methods show that the best results are obtained with a modified version of the DBS method combined with the iterative Fourier transform algorithm.

Visual secret sharing is the technique that divide the secret image into n multiple shares. Each share constitutes some information and when k shares out of n stack together the secret will reveal. However, less than k shares are not work. Sharing is the idea from secret sharing scheme that was presented in 1975 by Adi Shamir. The beauty of the visual secret sharing scheme is its decryption process i.e. To decrypt the secret using Human Visual System (HVS) without any computation. Visual cryptography is presented by Noar and Shamir in 1995 including also visual secret sharing. The resultant secret recover through this scheme is double in size of the original secret [17]. We have proposed the new algorithms for the (2, 2) visual cryptography and (3, 3) visual secret sharing. Our proposed schemes are for gray scale image and by stacking the shares, the resultant image achieved in same size with original secret image and Its shadow Image. We used randomization and pixel reversal approach in all methods.

Visual cryptography is a cryptographic method that encrypts visual facts and the information decrypted appears as an original visual image. Here, the confidential data is shared by dividing the visual details into multiple shares such that the encryption and the decryption are performed for reconstructing the original image back by stacking the splitted shares. However, the data sharing process lacks adequate security protection. To overcome the issues, this paper presents a robust visual cryptography-based data sharing scheme, named Competitive Swarm Improved Invasive Weed Optimization (CSIIWO) for sharing multiple data. Initially, the grayscale input image is shared between several parties, such that the shared image is encrypted and decrypted for retrieving the original image back. However, the cryptographic key generation is done using the devised CSIIWO algorithm such that the cryptographic keys are generated for the data sharing process to maintain confidentiality among multiple parties. Moreover, the devised method achieved the maximum Peak signal-to-noise ratio (PSNR) of 40.749 dB, minimum conditional privacy loss of 0.508, and maximum entropy of 7.987, respectively using Lena image. Furthermore, the proposed scheme can protect the multiple data sharing information and has numerous advantages compared with the previous mechanisms.