Wu-Lin Chen

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.

Tamper detection and image recovery for BTC-compressed images

To ensure the integrity of images compressed using block truncation coding (BTC), a tamper detection and image recovery scheme is proposed in this paper. In this scheme, the size of the authentication data can be adaptively selected according to the user’s requirement. The authentication data is embedded in the value differences of the quantization levels in each BTC-compressed image block. Multiple copies of the recovery data are embedded into the bit maps of the smooth blocks. Experimental results show that the proposed scheme performs well in terms of detection precision and the embedded image quality. Meanwhile, the tampered areas can be roughly recovered by using the proposed scheme.

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.

Probability-based image authentication scheme for indexed color images

Abstract. A tamper detection method to protect the integrity of indexed color images is presented. This method generates authentication codes of the indices based on the pseudorandom number generator. The length of authentication codes can be adaptively chosen according to the user’s requirement. The authentication codes are embedded into the index table of the indexed color image. In the tamper detection procedure, the embedded authentication codes are extracted. Besides, the pseudorandom number generator with the specific random seed is used to generate another set of authentication codes. By means of comparing the two sets of authentication codes, the tampered areas of the indexed color images can be found. Experimental results show that the proposed method efficiently detects the tampered areas while keeping good image qualities of embedded images.

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.

Refined codebook for grayscale image coding based on vector quantization

Abstract. Vector quantization (VQ) is a commonly used technique for image compression. Typically, the common codebooks (CCBs) that are designed by using multiple training images are used in VQ. The CCBs are stored in the public websites such that their storage cost can be omitted. In addition to the CCBs, the private codebooks (PCBs) that are designed by using the image to be compressed can be used in VQ. However, calculating the bit rates (BRs) of VQ includes the storage cost of the PCBs. It is observed that some codewords in the CCB are not used in VQ. The codebook refinement process is designed to generate the refined codebook (RCB) based on the CCB of each image. To cut down the BRs, the lossless index coding process and the two-stage lossless coding process are employed to encode the index table and the RCB, respectively. Experimental results reveal that the proposed scheme (PS) achieves better image qualities than VQ with the CCBs. In addition, the PS requires less BRs than VQ with the PCBs.

Residual Histogram Shifting Technique Based on Cascading Prediction for Reversible Data Hiding

To reversibly embed the secret data into the host image, the histogram shifting (HS) technique was proposed by embedding 1-bit secret data into the pixels in the peak points. To improve the hiding capacity of the histogram shifting technique, the residual histogram shifting (RHS) technique had been proposed. The prediction errors in the peak points of the residual histogram are used to embed the secret data. To further improve the hiding capacity, an improved block-based residual histogram shifting technique is proposed in this paper. The cascading prediction mechanism is employed in the proposed technique to generate the prediction errors for each image block. Experimental results reveal that the proposed technique provides higher hiding capacity than HS and RHS while keeping good image qualities of the embedded images.

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.