Chun-Chi Lo

A novel reversible image authentication scheme for digital images

Image authentication is to protect the image integrity when the digital image is illegally modified. Most of the image authentication schemes proposed so far employed the irreversible data hiding approach to embed the authentication data into the cover images. In this paper, a novel reversible image authentication scheme for digital images is proposed. In the proposed scheme, the authentication codes are generated by using the random number values induced by the selected random number seed. Then, the authentication codes are embedded into the cover image. Experimental results show that the proposed scheme achieves good detecting accuracy while keeping good image quality of the embedded image. The proposed reversible image authentication can be employed to protect the image integrity of the general-purposed images as well as the special-purposed images such as the medical and military images.

A novel tamper detection scheme for BTC-compressed images

A novel image authentication scheme for the compressed images of block truncation coding (BTC) is proposed in this paper. In the proposed scheme, 1-bit authentication data is generated from the quantization levels of each image block. Multiple block permutations are generated by using the random sequences induced by the selected random number seeds. Multiple copies of the authenticaiton data are embedded into the bit maps of BTC-compressed image blocks based on the block permutations. Experimental results show that the proposed scheme achieves good detecting accuracy while keeping good image quatiy of the embedded image.

Improved vector quantization scheme for grayscale image compression

This paper proposes an improved image coding scheme based on vector quantization. It is well known that the image quality of a VQ-compressed image is poor when a small-sized codebook is used. In order to solve this problem, the mean value of the image block is taken as an alternative block encoding rule to improve the image quality in the proposed scheme. To cut down the storage cost of compressed codes, a two-stage lossless coding approach including the linear prediction technique and the Huffman coding technique is employed in the proposed scheme. The results show that the proposed scheme achieves better image qualities than vector quantization while keeping low bit rates.

Efficient VQ-based image coding scheme using inverse function and lossless index coding

A novel image coding scheme based on vector quantization (VQ) is proposed in this paper. The goal of the proposed scheme is to provide better image qualities of the compressed grayscale images while keeping low bit rates. To achieve the goal, the encoding of the inverse image block is cooperated with the VQ scheme. In addition, the lossless index coding process is employed in the proposed scheme to cut down the required bit rates. From the results, it is shown that the proposed scheme achieves better image qualities than VQ while keeping low bit rates.

Efficient greyscale image compression technique based on vector quantization

In this paper, a novel greyscale image coding technique based on vector quantization (VQ) is proposed. In VQ, the reconstructed image quality is restricted by the codebook used in the image encoding/decoding procedures. To provide a better image quality using a fixed-sized codebook, the codebook expansion technique is introduced in the proposed technique. In addition, the block prediction technique and the relatively address technique are employed to cut down the required storage cost of the compressed codes. From the results, it is shown that the proposed technique adaptively provides better image quality at low bit rates than VQ.

Probability-based reversible image authentication scheme for image demosaicking

In this paper, we propose a novel image authentication scheme to detect the tampered areas for image demosaicking with the reversibility preserving property. Image demosaicking is the process of reconstructing an RGB color image from the sampled data acquired by the digital camera that applies a color filter array to a single sensor. In the proposed scheme, the authentication data is embedded into the rebuilt components of the demosaicked pixels.From the results, it is shown that good image qualities of the embedded images are obtained by using the proposed scheme. When the illegal users modified the contents of the embedded images, the tampered areas in the modified images can be clearly detected by using the proposed scheme. The demosaicked images can be losslessly recovered if no modifications are done on the embedded images. The proposed authentication codes embedding process can be implemented by hardware in single sensor digital camera. Furthermore, the proposed scheme can be extended to protect the image integrity for cloud computing environments. A reversible tamper detection scheme for demosaicked images is proposed.The authentication data is embedded the un-sampled components of the demosaicked pixels.The tampered areas in the modified images can be clearly detected by using the proposed scheme.The proposed scheme can be applied to any image demosaicking technique subject to image integrity protection.

Image vector quantization using geometric transform and lossless index coding

Abstract. We propose an efficient image-coding scheme based on vector quantization (VQ). Typically, image qualities of the compressed images by using VQ are restricted by the codebook used. To provide better image qualities of the compressed images while keeping low bit rates, encoding the geometric transformed image block is associated with VQ. To cut down the bit rates, the index table is further processed by the lossless index coding process. According to the results, it is shown that the proposed scheme achieves better image qualities than VQ while keeping low bit rates.

Variable-rate colour image quantization based on quadtree segmentation

A novel variable-sized block encoding with threshold control for colour image quantization (CIQ) is presented in this paper. In CIQ, the colour palette used has a great influence on the reconstructed image quality. Typically, a higher image quality and a larger storage cost are obtained when a larger-sized palette is used in CIQ. To cut down the storage cost while preserving quality of the reconstructed images, the threshold control policy for quadtree segmentation is used in this paper. Experimental results show that the proposed method adaptively provides desired bit rates while having better image qualities comparing to CIQ with the usage of multiple palettes of different sizes.

On a predictive scheme for colour image quantization

In this paper we proposed an improved colour image quantization scheme based on predictive coding. Since the neighbouring colour pixels are quite similar in most colour images, the similarity among the encoded pixels is exploited. In the proposed scheme the encoded distinct neighbouring colours are collected to form a smaller state-palette. If the closest colour in the state-palette is quite similar to the current encoding colour pixel, the index of the closest colour in the state-palette is recorded. Otherwise, the closest colour in original colour palette for the current encoding colour pixel is searched and the corresponding index is recorded. The experimental results show that the proposed method achieves good image qualities while requiring much lower bit rates for colour image compression.