C-C Chang

An effective codebook search algorithm for vector quantization

Abstract A new scheme that aims to cut down on the computational cost of the vector quantization (VQ) encoding procedure is proposed in this paper. In this scheme, the correlation between the codewords in the codebook is exploited and three test conditions are designed to filter out the impossible codewords in the codebook. The design of test conditions is based on the concept of integral projection. From the experimental results, it is shown that the new scheme outperforms all the other schemes proposed so far in speeding up the VQ encoding procedure. When the codebook of 1024 codewords is used in the proposed scheme, the execution time it consumes is less than 2 per cent of that needed by the full search algorithm. The average time reduction rate is approximately 97.7 per cent compared to the execution time for the full search algorithm. In other words, the proposed scheme indeed provides an effective approach to speed up the VQ encoding procedure.

A copyright protection scheme of images based on visual cryptography

Abstract This paper proposes a new scheme for effective protection of the intellectual property rights of digital images. Advantage is taken of visual cryptography to construct a master share from a digital image, and there is an ownership share for each copyright. After stacking of these two shares, the ownership information can be recovered directly by the naked eye without any computation. The method proposed will not change the host image and can be invisible, and moreover it can cast multiple ownerships into an image independently. Moreover, the method has high security, so that pirates and attackers will be unable to detect ownership information and fake the ownership of an image. Experimental results show that, after JPEG lossy compression, blurring, noise adding and cropping attacks, the ownership can still be robustly detected from the host image by the new method.

Novel image authentication scheme based on quadtree segmentation

Abstract In this paper, a new image authentication scheme based on quadtree segmentation is presented. In this scheme, partial digital signature encryption is employed to ascertain the origin of the image. Furthermore, the quadtree structure is imposed on the design of the authentication code. The authentication code consists of the quadtree list and the mean values of the quadtree leaf nodes. The size of the authentication code is adaptively determined according to the image characteristics. In the experiments, JPEG and JPEG2000 lossy compression and malicious manipulations are employed to evaluate the validity of the proposed scheme. The experimental results show that this scheme permits some acceptable operations and can detect malicious manipulations. Furthermore, when a malicious manipulation is detected, the mean values of the quadtree leaf nodes can be applied to recover the manipulated areas.

Fragile watermarking scheme for digital image authentication using pixel difference

Abstract The article presents a novel fragile watermarking scheme based on the concept of pixel differencing for the integrity verification of digital images. The scheme uses the human visual system to embed the authentication data into the difference between the input pixel and the average of its neighbouring pixels. The new scheme is capable of outperforming others because it not only provides a securer, more efficient detecting procedure, but also offers better resultant image quality. To demonstrate how well the new scheme can work in detection ability and security, some experiments and security analyses are also included.

Residue number system oriented image encoding schemes

Abstract Image encoding technique is an important issue to protect the security of an image and to prevent the image from being eavesdropped over the Internet. In 2001, Ammar et al. proposed an image encoding scheme based on residue number system (RNS). To overcome the disadvantages of Ammar et al.s scheme, Wang et al. proposed a more efficient RNS image encoding scheme in 2004. However, these two image encoding schemes are insecure and inefficient. Thus, we propose two image encoding schemes using residue number system in this paper. Compared with the previous RNS image encoding schemes, the proposed schemes have the advantages of lower communication overhead, less moduli selection, higher security and fewer computation loads. Also, the experimental results show that the proposed two schemes are more secure, efficient and practical than the previous works.

Efficient optimal pixel grouping schemes for AMBTC

Abstract In the conventional absolute moment block truncation coding (AMBTC) scheme, the block mean value is taken as the threshold for pixel grouping. But, the use of the block mean value is not optimal in AMBTC subject to the reconstructed image quality. In this paper, two optimal pixel grouping schemes are put forward for AMBTC. The experimental results shows that the proposed schemes can significantly reduce the computational cost in finding optimal grouping of pixels.

A new data hiding strategy with restricted region protection

Abstract This paper proposes a novel data hiding scheme that aims to prevent certain regions from modifying. These regions are specified by users, and a location map is generated to indicate where the changeable pixels are located. To reduce the size of this extra information, the location map is compressed using modified Huffman coding, and the compressed code is embedded into cover images. The Huffman code and the secret information can be separated automatically during the extracting procedure, without knowing the size of the compressed code in advance. The experimental results show that our proposed scheme has flexibility in data hiding capacity and stego image quality control, and the regions can be preserved well. Thus, the proposed scheme can be applied to a wide variety of applications.

Image hiding scheme using modulus function and optimal substitution table

The simple least-significant-bit (LSB) substitution technique is the easiest way to embed secret data in the host image. To avoid image degradation of the simple LSB substitution technique, Wang et al. proposed a method using the substitution table to process image hiding. Later, Thien and Lin employed the modulus function to solve the same problem. In this paper, the proposed scheme combines the modulus function and the optimal substitution table to improve the quality of the stego-image. Experimental results show that our method can achieve better quality of the stego-image than Thien and Lin’s method does.

A secure image delivery scheme with regional protection capability using image inpainting and editing

Abstract In this paper, a secure image delivery scheme that can protect the privacy of secret region in the transmitted image is proposed. The secret region that requires protection is firstly analogised as the repairing and cloning region in the problems of image inpainting and editing. By inpainting and modified Poisson editing, the original protection region can effectively be concealed or disguised with other meaningful content. In the modified Poisson editing process, the twice Laplacian operator is used to improve the seamless transition on the boundary of protection region. The bits generated by the original content of the region are then reversibly embedded into the inpainted or disguised image to form the final protected image. The protected image can be delivered in channels securely, and the attacker cannot obtain the real content of the image without the keys. Experiments were conducted to show the effectiveness and security of the scheme.

Reversible watermarking schemes based on expansion embedding using pixel partition strategies

Abstract Reversible watermarking methods have drawn attention of many researchers in recent years because original cover objects can be completely restored upon extraction of embedded information. The prediction error expansion (PEE) embedding proposed by Thodi and Rodriguez can embed one information bit into one cover pixel and achieve good visual quality of watermarked images. However, the PEE method is not a generalised scheme and its embedding capacity measured by bit per pixel (bpp) and visual quality measured by peak signal-to-noise ratio (PSNR) can be improved. Thus, we propose two novel schemes based on the PEE method by using pixel partition strategies to improve embedding capacity and/or visual quality. The first proposed scheme makes the PEE method be generalised and the second proposed scheme can embed more than 1 bpp. Experimental results show that the proposed schemes can significantly improve visual quality of the watermarked images produced by the PEE method when embedding capacity falls within the range [0·1, 1]. In particular, when an embedding capacity belongs to the range [0·1, 0·5], in average, the first proposed scheme with K = 1 can improve the PSNR of the PEE method at least 13 dB for test images. In addition, when embedding capacity falls within the range [0·1, 1], in average, the second proposed scheme with K = 1 can improve the PSNR of the PEE method at least 14 dB for test images.