With the rise of neural networks and pre‐trained models such as BERT, abstractive text summarization techniques have received widespread attention. Nevertheless, traditional extractive text summarization methods still hold substantial research value due to their low computational cost, interpretability, and robustness. In algorithms like TextRank and its variants, graph nodes are typically constructed based on surface‐level lexical features. These graphs often fail to incorporate many contextual relationships, such as coreference relationships among nodes, resulting in fragmented representations of key concepts. For edge construction, a sliding window of size T is commonly used to connect word nodes within the window. However, these methods often fall short in modeling the rich contextual dependencies embedded in the document. Several recent studies have demonstrated that semantic graphs can effectively improve the accuracy of text summarization. In this paper, we construct a more interpretable semantic graph from syntax trees and propose a novel unsupervised algorithm based on the personalized PageRank algorithm for summary extraction. We utilize tree transformation methods to enrich word‐level information for graph construction, define node‐merging rules to reduce graph complexity, use coreference chains to merge coreferring entities across sentences for enriching contextual links, and introduce the concept of Meta Node sets to capture thematic relationships that are not fully represented by syntactic dependencies or coreference chains alone. By clustering semantically related words, Meta Nodes enhance the graph’s ability to reflect deeper contextual coherence across the document. Compared with previous TextRank‐based methods, our improvement yields significant ROUGE score boosts on the CNN‐DM dataset. While the method was developed and evaluated using English‐language datasets, its underlying design is language agnostic and can be adapted to other languages with suitable linguistic tools.

In this paper, we present a fast and accurate Nearest Neighbor (NN) search method in the Riemannian manifolds formed by a kind of structured data - symmetric positive definite (SPD) matrices. We use an ensemble of vocabulary trees based on hierarchical k-means clustering and query these trees to find the NN candidates in sub-linear time. As generating these vocabulary trees with widely used affine-invariant Riemannian metric (AIRM) will be very time-demanding, we propose to use the second-order approximation to AIRM (SOA-AIRM). We evaluate the proposed NN search algorithm in the application scenario of near-duplicate image detection in a large database. Experimental results demonstrate that the proposed method significantly outperforms state of the art techniques in terms of both accuracy and speed.

Indexing structure plays an important role in the application of fast near-duplicate image detection, since it can narrow down the search space. In this article, we develop a cluster of uniform randomized trees (URTs) as an efficient indexing structure to perform fast near-duplicate image detection. The main contribution in this article is that we introduce “uniformity” and “randomness” into the indexing construction. The uniformity requires classifying the object images into the same scale subsets. Such a decision makes good use of the two facts in near-duplicate image detection, namely: (1) the number of categories is huge; (2) a single category usually contains only a small number of images. Therefore, the uniform distribution is very beneficial to narrow down the search space and does not significantly degrade the detection accuracy. The randomness is embedded into the generation of feature subspace and projection direction, improveing the flexibility of indexing construction. The experimental results show that the proposed method is more efficient than the popular locality-sensitive hashing and more stable and flexible than the traditional KD-tree.

This paper presents an efficient coarse-to-fine strategy for near duplicate image detection in a Riemannian space. At the coarse level, we use the faster but less accurate log-Euclidean Riemannian metric to search the entire database to retrieve a subset of the images that are likely to contain the near duplicates of the querying image; and at the fine level, we use the more accurate but computationally more demanding affine-invariant Riemannian metric to search the coarse level results to accurately identify near-duplicates. We present experimental results to show that the new coarse to fine strategy can be over 20 times faster than existing techniques using affine-invariant Riemannian metric without sacrificing accuracy.

This paper presents a framework for near-duplicate image detection in a visually salient Riemannian space. A visual saliency model is first used to identify salient regions of the image and then the salient region covariance matrix (SCOV) of various image features is computed. SCOV, which lies in a Riemannian manifold, is used as a robust and compact image content descriptor. An efficient coarse-to-fine Riemannian (CTOFR) image search strategy has been developed to improve efficiency while maintaining accuracy. CTOFR first uses a computationally fast but less accurate log-Euclidean Riemannian metric to do a coarse level search of the entire database and retrieve a subset of likely targets and then uses a computationally expensive but more accurate affine-invariant Riemannian metric to search the returns from the coarse search. We present experimental results to demonstrate that SCOV is a very compact, robust, and discriminative descriptor which is competitive to other state-of-the-art descriptors for near-duplicate image and video detection. We show that CTOFR can yield significant speedups over traditional full search methods without sacrificing accuracy, and that the larger the database the higher the speedup factor.

This paper introduces the covariance matrix of visually salient image features as a compact and robust descriptor for near duplicate image and video copy detection. We make two novel contributions. We first present a fast method for computing information theoretic based visual saliency maps using a data independent fast transform to replace the conventional data dependent computationally demanding transforms. We then introduce salient covariance (SCOV) - the covariance matrix of various image features within the visually salient regions and use SCOV for near duplicate image and video copy detection. We present experimental results to show that our new fast visual saliency computation technique improves efficiency without compromising performances. We demonstrate that SCOV is a very compact and robust feature for near duplicate image and video copy detection. Compared to popular features such as GIST, SCOV is not only more robust against various manipulations but also can be over 20 times more compact whilst achieving the same or better performances.