The reversible data hiding in encrypted images (RDH-EI) technique has been widely used to achieve privacy protection and convenient management of cloud storage images. The existing RDH-EI methods ...focus on the embedding capacity, reversibility, and the quality of decrypted images. This paper considers a new performance indicator of RDH-EI, the file size of encrypted images, which directly affects the cloud storage cost of content owner and network transmission efficiency. The goal is to obtain the smallest file size and to vacate sufficient space for data embedding. We propose a multi-MSB compression method that includes three strategies: the iterative MSBs-inversion prediction (IMIP), the adjacent prediction plane XOR (APPX), and the block variable length coding (BVLC). The file size of encrypted images is adaptively minimized while ensuring the format compatibility and lossless reconstruction. An encrypted image is generated by a combination of stream ciphers and bit scrambling to improve the resistance to various attacks such as the cipher-only attack (COA). Experimental results demonstrate that the proposed method has higher embedding capacity and resistance to COA compared with the current state-of-the-art methods for images with different texture complexity. The proposed algorithm can achieve the maximum embedding rate ranging from 0.74 to 4.78 bpp.
The decentralized coded caching scheme of Maddah-Ali and Niesen for the shared link network achieves an order-optimal memory-load tradeoff when the file size goes to infinity. It is then successively ...shown by Shanmugam et al. that, in the practical operating regime where the file size is finite, such a scheme yields a much less attractive coded caching gain. In this paper, we focus on designing decentralized coded caching schemes that can achieve low worst case loads of the shared link when the file size is finite and maintain order-optimal memory-load tradeoffs when the file size grows to infinity. First, we propose a decentralized coded caching design framework for designing decentralized coded caching schemes that can achieve significantly lower worst case loads than Maddah-Ali-Niesen's decentralized coded caching scheme in the finite file size regime while maintaining order-optimal memory-load tradeoffs when the file size grows to infinity. Then, within the proposed framework, we propose a decentralized coded caching scheme, which is simple and tractable, and can achieve a low worst case load in both the finite and infinite file size regimes. We analyze the worst case load of the proposed scheme and show that it outperforms Maddah-Ali-Niesen's and Shanmugam et al.'s decentralized schemes in the finite file size regime when the number of users is not too small. We also analyze the asymptotic worst case load of the proposed scheme when the file size goes to infinity and show that the proposed scheme achieves an order-optimal memory-load tradeoff. Finally, we analytically characterize the behavior of the worst case coded caching gain of the proposed scheme as a function of the required file size when the file size is large.
The most commonly used setting in the coded caching literature consists of the following four elements: (i) homogeneous file sizes, (ii) homogeneous cache sizes, (iii) user-independent homogeneous ...file popularity (i.e., all users share the same file preference), and (iv) worst-case rate analysis. While recent results have relaxed some of these assumptions, deeper understanding of the full heterogeneity setting is still much needed since traditional caching schemes place little assumptions on file/cache sizes and almost always allow each user to have his/her own file preference through individualized file request prediction. Taking a microscopic approach, this paper characterizes the exact capacity of the smallest 2-user/2-file (<inline-formula> <tex-math notation="LaTeX">N=K=2 </tex-math></inline-formula>) problem but under the most general setting that simultaneously allows for (i) heterogeneous files sizes, (ii) heterogeneous cache sizes, (iii) user-dependent file popularity, and (iv) average-rate analysis. Solving completely the case of <inline-formula> <tex-math notation="LaTeX">N=K=2 </tex-math></inline-formula> could shed further insights on the performance and complexity of optimal coded caching with full heterogeneity for arbitrary <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula>.
•We propose a reversible data hiding method for JPEG bitstream using optimal mapping.•The proposed method introduces a new objective to take the file size into consideration.•The optimization ...utilizes the value transfer matrix to simulate the VLC replacement.•It can provide a better trade-off between the file size increase and the capacity.
The traditional RDH method for JPEG bitstream is conducted by building the mapping between the variable length codes (VLC). However, the capacity is limited, and the file size may not be well preserved as the capacity is increased. This is because that the trade-off between the capacity and the file size has not been deeply investigated, neither explicitly formulated nor appropriately optimized. In this paper, we propose to take the file size preservation into consideration and minimize the file size increase for a given capacity. We use the value transfer matrix to simulate a theoretical model and then design some optimization rules to reach the reversible solution. Consequently, a better reversible VLC mapping can be obtained in terms of both the capacity and the file size preservation. The experimental results show that the proposed method can increase the capacity with a relatively low cost of file size increase.
Cloud computing offers advantages in handling the exponential growth of images but also entails privacy concerns on outsourced private images. Reversible data hiding (RDH) over encrypted images has ...emerged as an effective technique for securely storing and managing confidential images in the cloud. Most existing schemes only work on uncompressed images. However, almost all images are transmitted and stored in compressed formats such as JPEG. Recently, some RDH schemes over encrypted JPEG bitstreams have been developed, but these works have some disadvantages such as a small embedding capacity (particularly for low quality factors), damage to the JPEG format, and file size expansion. In this study, we propose a permutation-based embedding technique that allows the embedding of significantly more data than existing techniques. Using the proposed embedding technique, we further design a large-capacity RDH scheme over encrypted JPEG bitstreams, in which a grouping method is designed to boost the number of embeddable blocks. The designed RDH scheme allows a content owner to encrypt a JPEG bitstream before uploading it to a cloud server. The cloud server can embed additional data (e.g., copyright and identification information) into the encrypted JPEG bitstream for storage, management, or other processing purpose. A receiver can losslessly recover the original JPEG bitstream using a decryption key. Comprehensive evaluation results demonstrate that our proposed design can achieve approximately twice the average embedding capacity compared to the best prior scheme while preserving the file format without file size expansion.
Aim
To determine factors that may influence treatment outcome and healing time following root canal treatment.
Methodology
Root filled and restored teeth by pre‐doctoral students were included in ...this study. Teeth/roots were followed‐up regularly, and treatment outcome was evaluated at every follow‐up appointment (healed, healing, uncertain or unsatisfactory). Host (age, immune condition, pulp/periapical diagnosis, tooth/root type, location and anatomy) and treatment factors (master apical file size, apical extension, voids and density of root filling) were recorded from patient dental records. Univariate, bivariate and multivariate analyses were performed to determine the impact of the factors on treatment outcomes and healing times.
Results
A total of 422 roots from 291 teeth met the inclusion criteria with a mean follow‐up period of 2 years. The preoperative pulp condition, procedural errors during treatment, apical extension and density of root fillings significantly affected the treatment outcome. The average time required for a periapical lesion to heal was 11.78 months. The healing time increased in patients with compromised healing, patients older than 40 years, roots with Weine type II root canal systems, root canal systems prepared to a master apical file size <35, and roots with overextended fillings (P < 0.1).
Conclusion
Multiple host and treatment factors affected the healing time and outcome of root canal treatment. Follow‐up protocols should consider these factors before concluding the treatment outcome: patient's age, immune condition, as well as roots with overextended fillings, root canal systems with smaller apical preparations (size <35) or roots with complex canal systems. Intervention may be recommended if the treatment quality was inadequate or if patients became symptomatic.
Image encryption techniques can be used to ensure the security and privacy of valuable images. The related works in this field have focused more on raster images than on compressed images. Many ...existing JPEG image encryption schemes are not quite well compatible with the JPEG standard, or the file size of an encrypted JPEG image is apparently increased. In this paper, a novel bitstream-based JPEG image encryption method is presented. First, the groups of successive DC codes that encode the quantized DC coefficient differences with the same sign are permuted within each group. Second, the left half and the right half of a group, whose size will increase with the number of iterations, of consecutive DC codes may be swapped with each other, depending on whether an overflow of quantized DC coefficients occurs during decoding. Third, all AC codes are classified into 63 categories according to their zero-run lengths, then the AC codes within each category are, respectively, scrambled. Finally, all MCUs, except for DC codes, are randomly shuffled as a whole. Moreover, an image-content-related encryption key is employed to provide further security. The experimental results show that the file size of an encrypted JPEG image is almost the same as that of the corresponding plaintext image except for slight variations because of byte alignment. In addition, the quantized DC coefficients decoded from an encrypted JPEG image will not fall outside the valid range. Improved format compatibility is provided compared with other related methods. Moreover, it is unnecessary to perform entropy encoding again because all of the encryption operations are performed directly on the JPEG bitstream. The proposed method proves to be secure against brute-force attacks, differential cryptanalysis, known plaintext attacks, and outline attacks. Our proposed method can also be applied to color JPEG images.
Reversible data hiding (RDH) can be used to imperceptibly embed data into images in a reversible manner. Many RDH schemes have been developed for uncompressed images. However, JPEG compressed images ...are more widely used in our daily lives. The existing RDH techniques for JPEG images may cause significant distortion or a large increase in the file size of marked images. In this paper, a novel RDH scheme for JPEG images is proposed. First, the negative influence models of data embedding, including image visual distortion model and file size change model, are mathematically established. Then, a negative index for each frequency is defined as the weighted sum of the normalized average image visual distortion and the normalized average file size change per 1-bit hidden data, and the frequencies with small negative indices will be used for data embedding with a high priority. The weighting factor can be adjusted according to the user's preference for less image distortion or smaller file size. Lastly, secret data is embedded into non-zero quantized AC coefficients of the selected frequencies in ascending order of zero-run length. Extensive experiments conducted on typical images and a well-known image database show that the presented negative influence models are effective, and the proposed RDH scheme based on the models can achieve low image distortion and small increase in the file size of marked images.
Change in 10‐K file size robustly and negatively predicts future stock returns. The documented return predictability reflects mainly information content of 10‐K file size change on future cash flow ...news. We examine whether this return predictability derives from managers' risk disclosures or disclosure obfuscation. We find that the return predictability increases in future return horizon. It is driven by positive file size changes and is stronger for firms with high information asymmetry. It is stronger when managers have more “skin in the game.” It persists even when investor attention is high. It derives from the component of file size change that cannot be explained by business fundamentals. Although word count changes in specific 10‐K items can predict future stock returns, word count change in Item 1A, the risk disclosure section, has no return predictability. Our findings are broadly consistent with the managerial disclosure obfuscation explanation and suggest that lengthier 10‐K disclosure, to the extent it is used by managers to obfuscate bad news, does not necessarily benefit shareholders.
