Xiaotian Wu

Improving the visual quality of random grid-based visual secret sharing

Pixel expansion and visual quality of the revealed secret image are two major concerns in visual secret sharing (VSS). Random grid (RG) is an alternative approach to solve the pixel expansion problem by making the share as big as the original secret image, at the expense of sacrificing the visual quality of the reconstructed secret image. In this paper, two algorithms, including a contrast-enhanced RG-based VSS and a void-and-cluster-based (VAC-based) post-processing, are introduced to improve the reconstructed image quality. Experimental results and theoretical analysis are provided, illustrating that competitive visual quality is obtained by combined use of the two proposed methods. Highlights? We propose two methods to improve the visual quality of RG-based VSS. ? A contrast-enhanced VSS is to increase the contrast of revealed secret image. ? A VAC-based post-processing is adopted to obtain smooth-looking. ? The post-processing can be applied to size invariant probabilistic VSS.

High-capacity reversible data hiding in encrypted images by prediction error

In recent years, signal processing in encrypted images received much attention from academia due to the privacy preserving property. Reversible data hiding in encrypted images is a technique that embedded additional data into an encrypted image without accessing the content of the original image, the embedded data can be extracted and the encrypted image can be recovered to the original one. In this paper, two reversible data hiding methods in encrypted images, namely a joint method and a separable method, are introduced by adopting prediction error. In the joint method, data extraction and image reconstruction are performed at the same time. The reversibility, number of incorrect extracted bits are significantly improved while maintaining good visual quality of recovered image, especially when embedding rate is high. In the separable method, data extraction and image recovery are separated. The separable method also provides improved reversibility and good visual quality of recovered image for high payload embedding.

Random grid-based visual secret sharing with abilities of OR and XOR decryptions

Random grid (RG) is a methodology to construct visual secret sharing (VSS) scheme without pixel expansion. In some reported RG-based VSS schemes, a secret image can be visually reconstructed only by stacking operation, even thought some light-weight computational devices are available. In this paper, a novel RG-based VSS is developed, where the secret image can be recovered in two situations: (1) when computational devices are not available, the secret image can be reconstructed by stacking the shares directly, and (2) when some light-weight computational devices are available, the secret image can be decrypted by XOR operation. Further, the decrypted secret image quality by stacking operation is approximately the same as that of conventional RG-based VSS. But better visual quality is obtained by XOR operation.

Generalized Random Grid and Its Applications in Visual Cryptography

Random grid (RG) is a method to implement visual cryptography (VC) without pixel expansion. However, a reconstructed secret with lower visual quality reveals in RG-based VC due to the fact that average light transmission of a share is fixed at 1/2. In this work, we introduce the concept of generalized RG, where the light transmission of a share becomes adjustable, and adopt generalized RG to implement different VC schemes. First, a basic algorithm, a (2,2) generalized RG-based VC, is devised. Based on the (2,2) scheme, two VC schemes including a (2,n) generalized RG-based VC and a (n,n) xor-based meaningful VC are constructed. The two derived algorithms are designed to solve different problems in VC. In the (2,n) scheme, recovered image quality is further improved. In the (n,n) method, meaningful shares are constructed so that the management of shadows becomes more efficient, and the chance of suspicion on secret image encryption is reduced. Moreover, superior visual quality of both the shares and recovered secret image is achieved. Theoretical analysis and experimental results are provided as well, demonstrating the effectiveness and advantages of the proposed algorithms.

A user-friendly secret image sharing scheme with reversible steganography based on cellular automata

Secret image sharing is a mechanism to protect a secret image among a group of participants by encrypting the secret into shares and decrypting the secret with sufficient shares. Conventional schemes generate meaningless shares, which are hard to identify and lead to suspicion of secret image encryption. To overcome these problems, sharing schemes with steganography were presented. The meaningless shared data were embedded into the cover image to form stego images. However, distorted stego images cannot be reverted to original. In this work, a novel secret image sharing scheme with reversible steganography is proposed. Main contribution of this work is that two-dimensional reversible cellular automata with memory is utilized to encrypt a secret image into shared data, which are then embedded into cover image for forming stego images. By collecting sufficient stego images, not only the secret image is lossless reconstructed, but also distorted stego image is reverted to original. Simulation results shows that low computation cost and pleasing stego image quality are also achieved by the proposed scheme.

Robust copyright protection scheme for digital images using overlapping DCT and SVD

In this paper, a robust lossless copyright protection scheme, based on overlapping discrete cosine transform (DCT) and singular value decomposition (SVD), is presented. The original host image is separated into overlapping blocks, to which the DCT is applied. Direct current (DC) coefficients are extracted from the transformed blocks to form a DC-map. A series of random positions are selected on the map and SVD is performed to construct an ownership share which is used for copyright verification. Simulation results are carried out, demonstrating the robustness of the proposed scheme against different image-manipulation attacks.

Random grid-based visual secret sharing for general access structures with cheat-preventing ability

Conventional visual secret sharing (VSS) encodes a secret image into shares which are m times as big as the secrets. m is called pixel expansion. Random grid (RG) is an approach to solve pixel expansion problem. However, the existing VSS methods using RGs are confined to (2,n),(n,n) and (k,n). In this paper, RG-based VSS schemes for general access structures are proposed. The proposed algorithms can encode one secret image into n random grids while qualified sets can recover the secret visually. Furthermore, a cheating immune method is also presented to provided extra ability of cheat-preventing for RG-based VSS. Experimental results demonstrate that both the RG-based VSS for general access structures and cheating immune method are effective. More complicated sharing strategies can be implemented.

Visual secret sharing for general access structures by random grids

Visual secret sharing (VSS) is a way to protect a secret image among a group of participants by using the notions of perfect ciphers and secret sharing. However, each share generated by conventional VSS is m times as big as the original secret image, where m is called pixel expansion. Random grid (RG) is an alternative approach to implement VSS without pixel expansion. However, reported RG-based VSS methods are threshold schemes. In this study, RG-based VSS for general access structures is presented. Secret image is encoded into n RGs while qualified sets can recover the secret visually and forbidden sets cannot. The proposed scheme is a generalisation of the threshold methods, where those reported RG-based schemes can be considered as the special cases of the proposed scheme. Experimental results are provided, demonstrating the effectiveness and advantages of the proposed scheme.

Non-expansible XOR-based visual cryptography scheme with meaningful shares

XOR-based visual cryptography (VC), a brand-new type of VC, is suitable for solving the low image quality and alignment problems in VC system. However, meaningless share and pixel expansion remain to be continuing challenges in existing XOR-based VC. To fix those mentioned defects, XOR-based VC with meaningful shares is introduced in this paper. A basic algorithm implemented by a simple 2 n i? n matrix for constructing a (n,n) XOR-based VC is first proposed. In the following stage, a (n,n) XOR-based VC with meaningful shares is investigated by adopting the basic algorithm, where the meaningful share can be directly generated without extra process. Extensive experimental results are demonstrated, exhibiting the effectiveness and advantages of the proposed method. Further, sufficient theoretical proofs are provided for illustrating the correctness of the proposed XOR-based VC. HighlightsA non-expansible XOR-based VC scheme with meaningful shares is introduced.Meaningful shares is constructed without extra hiding process.Sufficient theoretical analysis on the proposed scheme is provided.Superior visual quality of both the share and revealed image is achieved.

Extended Capabilities for XOR-Based Visual Cryptography

The XOR-based visual cryptography (VC) is a possible methodology to solve the poor visual quality problem without darkening the background in VC. However, investigations on XOR-based VC are not sufficient. In this paper, we exploit some extended capabilities for XOR-based VC. Actually, two XOR-based VC algorithms are proposed, namely XOR-based VC for general access structure (GAS) and adaptive region incrementing XOR-based VC. The first algorithm aims to implement complicated sharing strategy using GAS, while maintaining merits such as perfect reconstruction of secret, no pixel expansion, and no code book requirement. In the second algorithm, the concept of adaptive security level is first introduced, where the security levels are recovered in accordance with the qualified sets instead of the quantity of stacked shares. Adaptive region incrementing XOR-based VC further enriches the application scenarios. Theoretical analysis on the proposed algorithms are provided, as well as extensive experimental results and evaluations for demonstrating the effectiveness and advantages of the two methods.