Abstract:
In this paper, the authors propose a new steganographic scheme based on vector quantisation (VQ) andsearch-order coding (SOC).The capacity of the proposed scheme is higher than others based on VQand the quality ofstego-image is acceptive. In general, the capacity of the schemes based on VQ is usually 1-bit per block. In 2004, Yuet al. proposed a scheme to increase the capacity to 3-bit per pair of blocks. In the proposed scheme, the authorsutilised multiple codebooks and chose the combinations of per pair of blocks, to embed the secret data.The capacitywas increased to 6-bit per pair of blocks, and the quality was identical Yu et al.’s scheme.
1 Introduction
Computer and network communication techniques havedeveloped quickly in recent years People attach greatimportance to secret communication. For this reason,hidden information is being proposed. Hidden informationtechniques are mainly classified into two categories:copyright marking and steganography [1]. Copyrightmarking such as a signature or a trademark is used toembed copyright information into the host image, thusensuring the copyright. The emphasis on copyrightmarking is that the watermark hidden in the host imagemust be able to be retrieved, even if the stego-image hasbeen subjected to lots of manipulation, such as cropping,lossy compression, resizing etc. A watermark is usually verysmall and composed of visible and imperceptible images.Steganography is different from watermarking. The goal ofsteganography is to embed secret data into the host image, insuch a way that the interceptors perceive its presence. In otherwords, steganography provides a secret communication [2].The key issues in steganography are how to embed moresecret data and yet maintain the stego-image’s good quality.The technique of data hiding in images can be classifiedinto two categories: data hiding in spatial domain schemesand data hiding in frequency domain schemes. Neither datahiding in spatial domain schemes nor data hiding infrequency domain schemes can be used in other domains.The most well-known data hiding scheme in the spatialdomain is least-significant-bits substitution (LSB) [3]. Ituses the invisible to the human visual system differencesbetween the host image and stego-image to hide data.There are many well-known schemes based on LSB, suchas optimal LSB, LSB matching, pixel-value differencingmultiple-based notational system, and using side match[4–11]. There are some data hiding schemes using vectorquantisation (VQ) compression in the spatial domain,those are different from the schemes mentioned above[1, 12–15]. Due to a high compression of VQ, thecapacity for hiding data and the data traffic are much lessthan the mentioned schemes.In this paper, our proposed scheme is in the spatialdomain, based on VQ and search-order coding (SOC) [14,16]. Prior to this research, the capacity of the schemesbased on VQ was usually 1-bit per block [1, 12, 13]. In2004, Yu et al. [15] proposed a scheme to increase thecapacity to 3-bit per pair of blocks. In this paper, we usemultiple codebooks and choose different combinations ofper pair of blocks. The capacity is increased to 6-bit perpair of blocks, and the quality is as good as in Yu et al.’sscheme.


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