Research On Image-Based Lossless Information Hiding

With the continuing advancements in information technology, information storage, processing, reproduction, transmission becomes more and more convenient. However, all kinds of information in an open network environment can be easily eavesdropped and intercepted; all digital information can easily be copied, deleted, cut, spliced, tampered or forged. Therefore, information security is faced with enormous challenges that we have to face. As a basic information security tool, information/data hiding plays an important role in many critical areas of information security.However, in most cases of data hiding, the cover media may suffer some permanent distortions as a result of data hiding and can not be inverted back to the original one. These techniques have no advantages in the field of digital media content protection because the images processed by these techniques will lose their values. Therefore, in some applications, such as media content protection, it is desirable to reverse the stego-image back to the original cover image without any distortion after data extraction, i.e., the technique not only can embed secret data into a cover image, but also the original cover image can be recovered from the stego-image with no distortion after the hidden data have been extracted. Techniques with this property are referred to as lossless data hiding. Furthermore, the robustness of a lossless data hiding algorithm against non-malicious changes such as lossy compression or sometimes unavoidable addition of random noise which is below a certain level and does not change the content of an image can be useful in the context of reversible data hiding. It might enlarge the application scope of lossless data hiding technique as it enables the lossless data hiding to convey information in a lossy environment. Techniques with this property are referred to as robust lossless data hiding or lossless robust data hiding. According to the problems mentioned above, this dissertation, after a deep study on related works, mainly focused on images and launched the research in two aspects: high embedding capacity lossless data hiding and robust lossless data hiding. The main contributions are as follows.(1) A reversible data hiding scheme based on fixed reference pixel of block is proposed. The proposed scheme can offer high embedding capacity and keep low distortion. Furthermore, the proposed scheme can be implemented easily and no extra information except message length is needed to extract data and restore image. Experimental results show that the average pure payload among eight commonly used images can be greater than 0.97 bits per pixel (bpp) while maintaining all the PSNR values of the stego-images above 30 dB.(2) A lossless data hiding scheme based on scan path is proposed. Nine basic scan paths are defined, and this means all-directional adjacent pixel differences can be obtained. The proposed scheme can offer high embedding capacity and keep low distortion by choosing the best scan path and the optimized pixel difference. As experimental results have shown, the average pure payload among eight commonly used images can be greater than 1.0 bits per pixel (bpp) while all the PSNR values of the stego images remain larger than 30 dB.(3) An improved reversible data hiding scheme using dynamic reference pixel of block instead of the fixed reference pixel of block is proposed. The improved scheme uses the reference pixel whose value is the median value of the whole sorting sequence of block. The improved scheme can offer higher embedding capacity while mantaning the advantages of the original version. Experimental results have shown that the performance of the dynamic reference pixel of block outperforms that of the fixed reference pixel of block. The improved scheme has been applied to all of the 1338 images in UCID-Image Database (v2) which includes many different types of images, and the experimental results show that the average payload among these images is larger than 1.1 bits per pixel (bpp) while keeping the average PSNR values 30.8 dB.(4) A robust lossless data hiding scheme based on statistic shifting is proposed, in which a statistic is introduced and bits can be embedded by shifting the statistic. The shift quantity and shifting rule are fixed for all blocks, and reversibility is achieved. On the other hand, owing to the separation of bit-0-zone and bit-1-zone as well as the particularity of the statistic, minor alteration applying to the stego-image generated by non-malicious attacks such as JPEG compression will not cause the bit-0-zone and the bit-1-zone to overlap, and robustness is achieved. Experimental results show that, compared with previous works, the performance of the proposed scheme is significantly improved.(5) An improved robust lossless data hiding scheme based on statistic shifting is proposed. In the original version, the embedding mechanism lets only one group of pixels of block change, leading to two disadvantages. First, to shift a statistic to different zones cause a group of pixels to be altered greatly, leading to a low image quality. Second, the hidden data can not resist the JPEG compression at high compression levels during lossy compression, leading to a weak robustness. The improved scheme uses a new embedding mechanism to block and two groups of pixels of block can be changed. Experimental results show that, compared with the previous version, the performance of new scheme is significantly improved in terms of image quality and robustness.