Tung-Shou Chen

A steganographic method based upon JPEG and quantization table modification

In this paper, a novel steganographic method based on joint photographic expert-group (JPEG) is proposed. The proposed method modifies the quantization table first. Next, the secret message is hidden in the cover-image with its middle-frequency of the quantized DCT coefficients modified. Finally, a JPEG stego-image is generated. JPEG is a standard image and popularly used in Internet. The stego-image will not be suspected if we could apply a JPEG image to data hiding. We compare our method with a JPEG hiding-tool Jpeg-Jsteg. From the experimental results, we obtain that the proposed method has a larger message capacity than Jpeg-Jsteg, and the quality of the stego-images of the proposed method is acceptable. Besides, our method has the same security level as Jpeg-Jsteg.

A new encryption algorithm for image cryptosystems

Abstract There are two major differences of the characteristics of the text data and image data. One difference is that the size of image data is usually much larger than that of text data. The other is that plain data rarely permit loss when a compression technique is used, but image data do. In this paper, we design an efficient cryptosystem for images. Our method is based on vector quantization, which is one of the popular image compression techniques. Our method can achieve the following two goals. One goal is to design a high security image cryptosystem. The other goal is to reduce computational complexity of the encryption and decryption algorithms.

A virtual image cryptosystem based upon vector quantization

We propose a new image cryptosystem to protect image data. It encrypts the original image into another virtual image. Since both original and virtual images are significant, our new cryptosystem can confuse illegal users. Besides the camouflage, this new cryptosystem has three other benefits. First, our cryptosystem is secure even if the illegal users know that our virtual image is a camouflage. Second, this cryptosystem can compress image data. Finally, our method is more efficient than a method that encrypts the entire image directly.

Sharing multiple secrets in digital images

The share of multiple secrets among participants in secret transmission is a critical topic for a new digital image scheme. The new scheme is derived from the least significant bit substitution method and the visual cryptography method. Given some secrets and a set of cover images, the proposed scheme will convert the secrets into many bit planes and modify the cover images based on these bit planes. In our method, each participant has a unique modified cover image called a stego-image. A pair of participants can therefore reconstruct a unique secret without destroying of its secrecy. Experiments shown that the quality of all stego-images is visually acceptable. The proposed scheme also prevents anyone who possesses only one stego-image from gaining information about the secret and the other stego-image.

An Improved VQ Codebook Search Algorithm Using Principal Component Analysis

We present an improved codebook search algorithm in this paper. We call it thedouble test of principal components(DTPC). This algorithm speeds up the codebook search by searching only an appropriate sub-codebook instead of the whole set of codewords. Moreover, DTPC inherits several benefits from some previous techniques, such as the double test (DT) and the principal component analysis (PCA). Thus DTPC is much more efficient than the other algorithms. Simulation results confirm this efficiency. According to these results, the total number of the mathematical operations needed in DTPC is usually less than that needed in any other method, even if the MSE degradation of DTPC is limited within 0.13 dB. Furthermore, in some cases, this number of DTPC is only 3% of that in a full search.

A new scheme for sharing secret color images in computer network

Based on a visual cryptography scheme, an effective and generalized scheme of color image hiding is proposed. By means of little additional computations, it goes through a color index table to hide and recover a secret image. In this scheme, a secret color image hides itself in two arbitrary color images, which can be constructed and then are kept by two participants, separately. Note that the processed images are significant. It is a kind of camouflage. Later, the secret image can be recovered through the same simple algorithms on two camouflage color images. The paper proves that only one of the two camouflage color images cannot reveal the secret image. Thus, the hidden information is secured.

A new image coding algorithm using variable-rate side-match finite-state vector quantization

A new side-match vector quantizer, NewSMVQ, is presented in this paper. Three techniques are incorporated to improve the image quality, encoding speed, and bit rate for compressing images. The experimental result shows: i) the encoding time of NewSMVQ is almost 7 times faster than that of SMVQ (ordinary fixed-rate side-match vector quantizer) and CSMVQ (variable-rate SMVQ) and ii) NewSMVQ outperforms SMVQ and CSMVQ in terms of bit rate versus image quality tradeoffs.

Diagonal axes method (DAM): a fast search algorithm for vector quantization

Vector quantization (VQ) is a fundamental technique for image compression. But it takes time to search for a similar codeword in a codebook. Thus, the codebook search is one of the major bottlenecks in VQ. We propose a new search algorithm which is used to speed up both the codebook generation and the encoding. We call it the diagonal axes method (DAM). This new algorithm contains two major techniques: diagonal axes analysis (DAA) and orthogonal checking (OC). Since most of these procedures simply involve additions and subtractions, DAM is more efficient than some other related algorithms. Simulation results confirm this effectiveness.

A new scheme of progressive image transmission based on bit-plane method

The bit-plane method (BPM) is the simplest way to implement the progressive image transmission (PIT) system. In this paper, we propose a simple and effective method to improve the image quality of the BPM in each phase. This method generates a tree-structured codebook to describe the contents of the pixels of the transmitted image. By transmitting this tree structured codebook to the receiver level by level, we can increase the image quality of the BPM in each phase. The experimental results show that the image quality of our scheme turns out better than that of the BPM. Moreover, our scheme can better impress the human visual system in an earlier phase than the BPM.

New tree-structured vector quantization with closest-coupled multipath searching method

We propose a new method to improve the image quality and the encoding time of tree-structured vector quantization (TSVQ). We call this new method the closest-coupled tree-structured vector quantization (CCTSVQ). In this method, we use the closest-neighboring pointers to enlarge the search range of each search path and guide all search paths into more appropriate codewords. CCTSVQ therefore improves the image quality of TSVQ. This fact is shown in our experimental results. Furthermore, in these experimental results, we see that the encoding time of CCTSVQ is always faster than that of TSVQ, based on the same image quality.