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This study proposes two reversible data hiding (RDH) schemes for vector quantisation (VQ)-compressed images based on switching-tree coding (STC) and dynamic tree-coding scheme (DTCS). Most developed VQ-based RDH schemes produce non-legitimate codes as output. In order to preserve the legitimacy of the embedded VQ code, some schemes embed data into VQ indices by employing an index replacement mechanism and some other schemes perform embedding by adopting one of the possible ways during encoding each index when multiple ways are possible to encode the index. In the current research, two schemes are proposed based on the second mechanism. Outputted code of the proposed schemes is a legitimate STC/DTCS code and the conventional STC/DTCS decoder can decode it to the original VQ index table. The experimental results show that the proposed schemes are feasible and in comparison with some previous RDH schemes, the first one provides higher embedding capacity and the second one embeds a substantial amount of data while provides lower bit rate than most the previous schemes. In addition, the embedding-efficiency of both proposed schemes is higher than that of the previous schemes.
In which the attacker only has access to watermarked images. the Watermarked Only Attack (WOA), in which the attacker only has access to watermarked images the Known Message Attack (KMA),
in which the attack-er has access to several pairs of previously watermarked images and the associated messages. Certainly, the currently transmitted message bits are not known to the attacker.
In which the attack-er has access to several pairs of previously watermarked images and the associated messages. Certainly, the cur-rently transmitted message bits are not known to the attacker.
In which the attacker has access to several pairs of previously watermarked images and the corresponding cover image. Certainly, the current cover image is not known to the attacker.
Some data hiding schemes in the literature are reversible. In a reversible data hiding (RDH) scheme, the original cover media can be reconstructed completely after the embedded secret data is extracted. Since this capability is desirable or even may be essential in some applications such as military or medical imaging, some researchers have paid attention to develop reversible image data hiding schemes.
Image data hiding techniques can be performed in raw images or in compressed images. In order to save the storage space and the bandwidth, typically images are stored and transmitted in the compressed formats.
This paper proposes two new RDH schemes for VQ index tables, which employ the second mechanism of the above-mentioned mechanisms. The first scheme works based on the STC method and its output is a legitimate STC code, which can be decoded by the conventional STC decoder, and the second one works based on the DTCS and its output is a legitimate DTCS code, which can be decoded by the conventional DTCS decoder. The proposed schemes do not degrade the image quality.
Moreover, in comparison with some previous schemes, the proposed STC-based RDH scheme provides a more embedding capacity and also the proposed DTCS-based RDH scheme embeds a substantial amount of secret data while provides lower bit rate than most of the previous schemes. In addition, the embedding-efficiency of both proposed schemes is higher than that of the previous schemes.
This paper presented two RDH schemes for VQ-compressed images based on the STC and DTCS methods. Some VQ-based RDH schemes produce non-legitimate codes as output and some schemes, which employ an index replacement mechanism, produce stego-images with poor quality. In the proposed schemes, instead of exchanging the VQ indices, the data embedding is performed by adopting one of the possible ways of encoding when multiple ways are possible to encode the index. This mechanism preserves the legitimacy of the generated code. Consequently, the conventional STC/DTCS decoder can decode the embedded code obtained by the proposed STC-based/DTCS-based RDH scheme to the original VQ index table.
The proposed schemes have some advantages; they do not make any distortion in the VQ index table and they are more secure in comparison with the VQ-based schemes that generate non-legitimate codes as the output as well as the schemes that embed data by an index replacement mechanism. The experimental results confirmed that the proposed schemes are feasible and effective. The proposed STC-based RDH scheme provides higher capacity than some previous RDH schemes, and the DTCS-based RDH scheme embeds a substantial amount of secret data while provides a low bit rate of the embedded code in comparison with the proposed STC-based RDH scheme and some other existing RDH schemes. In addition, the embedding-efficiency of both proposed schemes is higher than that of the previous schemes.