In this paper, we present HomoGen, an enhanced video inpainting method based on homography propagation and diffusion models. HomoGen leverages homography registration to propagate contextual pixels as priors for generating missing content in corrupted videos. Unlike previous flow-based propagation methods, which introduce local distortions due to point-to-point optical flows, homography-induced artifacts are typically global structural distortions that preserve semantic integrity. To effectively utilize these priors for generation, we employ a video diffusion model that inherently prioritizes semantic information within the priors over pixel-level details. A content-adaptive control mechanism is proposed to scale and inject the priors into intermediate video latents during iterative denoising. In contrast to existing transformer-based networks that often suffer from artifacts within priors, leading to error accumulation and unrealistic results, our denoising diffusion network can smooth out artifacts and ensure natural outputs. Extensive experiments demonstrate the effectiveness of the proposed method qualitatively and quantitatively.

With the rapid evolution of advanced image compression, DNN-based learned image compression has emerged as the promising approach for transmitting images in many security-critical applications, such as cloud-based face recognition and autonomous driving, due to its superior performance over traditional compression. There is a pressing need to fully investigate the robustness of a classification system post-processed by learned image compression. To bridge this research gap, we explore the adversarial attack on Learned Image Compression Classification System (LICCS) that targets image classification models that utilize learned image compressors as preprocessing modules. To perform an adversarial attack on an image within the LICCS, the goal is to introduce the adversarial perturbation δ to the source image X that causes the reconstructed adversarial examples gs(Q(ga(X+δ))) to be misclassified by the classification model, which can be formulated as follows:\begin{equation*}\begin{array}{ll} {\mathop {\arg \max }\limits_i f{{\left({{g_s}\left({Q\left({{g_a}\left({{\mathbf{X + \delta }}}\right)}\right)}\right)}\right)}_i} \ne y,}&{{\text{s}}{\text{.t}}{\text{.}}\parallel \delta {\parallel _p} \leq \varepsilon .} \end{array}\tag{1}\end{equation*}

In this paper, we introduce an imperceptible adversarial attack approach designed to effectively degrade the reconstruction quality of LIC, resulting in the reconstructed image being severely disrupted by noise where identifying any object in the reconstructed image is virtually impossible. More specifically, we generate adversarial examples by introducing a Frobenius norm-based loss function to maximize the discrepancy between original images and reconstructed images from adversarial examples in order to corrupt the reconstructed image severely.

The Bj⊘ntegaard Delta rate (BD-rate) measurements have been used as the primary metrics to evaluate performance of video codecs. However, current BD-rate calculation methods are only applicable under the condition that the rate-distortion (R-D) values maintain a monotonic relationship, as this prerequisite is essential for computing integral along the distortion axis. To address this limitation, we propose a curve-fitting based BD-rate solution that guarantees the reconstructed R-D curve to be monotonic. Considering different use cases, we provide a four parameters logistic curve and a constraint cubic curve to approximate the underlying R-D curve. Computation of BD-rate and BD-metric using fitted R-D curve are elaborated in detail. Experimental results indicate that the proposed solutions work well on non-monotonic data. Furthermore, we verified through quantitative analysis that curve-fitting solutions provide more precise measurements of coding efficiency compared to interpolation methods. This improved accuracy contributed by the proposed methods is attributed to the higher resilience to the inherent randomness present in observed data. The proposed method has been adopted by the MPEG WG4 VCM study group for standardization activities. The source code was released at https://multimedia.tencent.com/resources/tvd.

Recently, Video Coding for Machines (VCM) has gained more and more attention due to its efforts in machine vision tasks. As a crucial track in VCM, feature compression preserves and transmits critical feature information for machine vision. Most existing studies employ dimensionality reduction to the raw multi-scale feature before compression. However, feature sparsity is left insufficiently considered in removing redundancy in compressed features. In this letter, we propose a novel framework for image feature compression for machines, where the multi-scale feature is hierarchically transformed into a sparse representation for compression. The multi-scale feature is first fused by convolutional neural networks and the attention mechanism. To introduce sparsity into the fused feature, informative channels are identified by a channel-wise binary mask where activated elements are sampled from the importance distribution of channels learned from feature content. Then, the fused feature is masked to generate a sparse representation for compression. Experiments conducted on two machine tasks show significant improvements in our model over state-of-the-art methods.

Learning-based image coding schemes, exemplified by JPEG AI, have shown potential by greatly exceeding the conventional image compression standards in rate-distortion (RD) performance. However, their widespread applications are hindered by high decoding complexity, particularly from the upsampling and attention modules. Existing works sought to reduce this complexity, but their solutions are not fully effective, leaving considerable complexity unaddressed. In this paper, we present a simplified transform network architecture that employs an optimized attention module, a streamlined upsampling module, and a pared-down activation function to tackle this issue. Simulation results show that the simplified decoder sees its complexity (measured by kMACs/pixel) reduced by 80% (from 833 to 172), while the gain over Versatile Video Coding (VVC) increases slightly (from 27.3% to 27.5%). Partial methods in this paper have been integrated into the JPEG AI Verification Model (VM) software.

We describe Substitutional Neural Image Compression (SNIC), a general approach for enhancing any neural image compression model, that requires no data or additional tuning of the trained model. It boosts compression performance toward a flexible distortion metric and enables bit-rate control using a single model instance. The key idea is to replace the image to be compressed with a substitutional one that outperforms the original one in a desired way. Finding such a substitute is inherently difficult for conventional codecs, yet surprisingly favorable for neural compression models thanks to their fully differentiable structures. With gradients of a particular loss back-propogated to the input, a desired substitute can be efficiently crafted iteratively. We demonstrate the effectiveness of SNIC, when combined with various neural compression models and target metrics, in improving compression quality and performing bit-rate control measured by rate-distortion curves.

While the Internet is open by design, it is still the case that users can be subject to censorship by governments or enterprises in accessing Web services and data. In this paper we propose SEnD, a fully-distributed censorship circumvention system built upon an overlay, where users have peer-to-peer virtual private IP tunnels to proxies within their social network. With SEnD, users in an uncensored area can act as proxy servers for their social friends in a censored area, allowing them to bypass the censorship. SEnD is able to outperform the current censorship techniques, such as IP address blocking and active probing attacks. We assessed the effectiveness of SEnD through extensive simulations based on a synthetic dataset, as well as experiments based on a prototype implementation. We built our synthetic dataset based on parameters obtained from questionnaires administered both inside and outside China (we consider China as a case study of censorship area). The results show that SEnD is feasible, efficient and scalable. For example, when the proportion of concurrent active users is less than 60, 99.9 percent of these users are able to find proxy servers.

This paper introduces DISPERSE, a distributed scalable architecture for delivery of content and services that provides resilience against node failure through location-independent storage and replication of content. Current content delivery networks (CDNs) have, at least to some degree, a centralized structure thus susceptible to a single point of failure. DISPERSE addresses this limitation by implementing a fully de-centralized structure. DISPERSE is a two-layer architecture: the first layer (front-end layer) exposes services (e.g., Web, SFTP) to clients; the second layer (back-end layer) provides reliable distributed storage of content and application state. Content in DISPERSE's back-end layer is stored and exchanged as Named Data Network (NDN) content objects. This allows DISPERSE to implement fine-grained, location-independent, fully decentralized content replication mechanisms. We validate the performance of DISPERSE under two node failure scenarios. In the first scenario, content can be stored in any DISPERSE node, and all nodes are equally likely to fail. In this scenario, we use non-linear optimization techniques to determine the optimal number of content copies under availability and latency constraints. In the second scenario, different nodes fail with different probabilities, and content is stored in nodes according to its value, node failure probability, and resource availability. This scenario is addressed as an instance of the minimum cost flow problem. Our results show that DISPERSE reduces the failure of content retrieval by five orders of magnitude compared to common CDN implementations, without significantly increasing content retrieval delay. Further, numerical results show that DISPERSE improves content availability by a factor of 1.3× - 2.3× when deploying the minimum cost flow algorithm.

Peer-to-peer systems are resilient in the presence of churn and uncorrelated failures. However, their behavior in extreme scenarios where massive correlated failures occur is not well-studied. Yet, there have been examples of situations where a country-scale fraction of Internet users have been disconnected from the rest of the network-for instance, when a government cuts connectivity to the outside world as a mechanism for suppression of uprisings. In this paper, we consider the effect of such partitions on topology and routing of structured and social-based unstructured P2P overlays, including a novel social-aware overlay. In particular, we consider nodes within a relatively small fraction of the network (2.5% or fewer Internet users), and study whether users can communicate with their (n-hop away) social neighbors in a peer-to-peer fashion after the partition. We perform an extensive simulation-based analysis to assess the probability for these communications to be possible. In our analysis, we consider both real and synthetic datasets of online social networks. Our results show that structured P2P overlay routability is severely hampered by country-scale partition events. In addition, the proposed social-based unstructured overlay network provides improved routability while maintaining a smaller number of links.