Adaptive approximate nearest neighbor search for fractal image compression

Nearest neighbor search is a fundamental problem in computer vision and machine learning. The straightforward solution, linear scan, is both computationally and memory intensive in large scale high-dimensional cases, hence is not preferable in practice. Therefore, there have been a lot of interests in algorithms that perform approximate nearest neighbor (ANN) search. In this paper, we propose a novel addition-based vector quantization algorithm, Asymmetric Mapping Quantization (AMQ), to efficiently conduct ANN search. Unlike existing addition-based quantization methods that suffer from handling the problem caused by the norm of database vector, we map the query vector and database vector using different mapping functions to transform the computation of L-2 distance to inner product similarity, thus do not need to evaluate the norm of database vector. Moreover, we further propose Distributed Asymmetric Mapping Quantization (DAMQ) to enable AMQ to work on very large dataset by distributed learning. Extensive experiments on approximate nearest neighbor search and image retrieval validate the merits of the proposed AMQ and DAMQ.

Compression of images process is a step in the image processing. It is concerned with the transmission and storage of digitally created images. Fractal coding is a potential image and video compression approach with good reconstruction fidelity and relatively large compression ratios, because of its simplicity and great performance; fractal image compression (FIC) is a particularly popular approach in image compression applications. However, it has a significant disadvantage in the form of a long encoding time. This is because encoding any small bit necessitates a massive similarity search in the original data As a result; the FIC search time is reduced while the quality of the reconstructed images is maintained acceptable level in many introduced paper and other still a study topic in progress. Fractal images are images that are self-similar in that each individual part is the same as the total. This paper will discusses many attempts for more author that working on image and video compression using fractal compression technique based on various approach and with each discuss focuses on the main parameter of compression such compression ratio (CR), peak signal to noise ratio (PSNR) and encoding time, as well as the details of data set the used for testing also writing with each technique to creating fractal video and image compression. Index Terms— FIC, Video compression, parallel processing, Iteration Function System (IFS), Image processing.

Exploiting lower bounds to accelerate approximate nearest neighbor search on high-dimensional data

Nearest neighbor search algorithms have been successful in finding practically useful solutions to computationally difficult problems. In the nearest neighbor search problem, the brute force approach is often more efficient than other algorithms for high-dimensional spaces. A special case exists for objects represented as sparse vectors, where algorithms take advantage of the fact that an object has a zero value for most features. In general, since exact nearest neighbor search methods suffer from the “curse of dimensionality,” many practitioners use approximate nearest neighbor search algorithms when faced with high dimensionality or large datasets. To a reasonable degree, it is known that relying on approximate nearest neighbors leads to some error in the solutions to the underlying data mining problems the neighbors are used to solve. However, no one has attempted to quantify this error or provide practitioners with guidance in choosing appropriate search methods for their task. In this thesis, we conduct several experiments on recommender systems with a goal to find the degree to which approximate nearest neighbor algorithms are subject to these types of error propagation problems. Additionally, we provide persuasive evidence on the trade-off between search performance and analytics effectiveness. Our experimental evaluation demonstrates that a state-of-the-art approximate nearest neighbor search method (L2KNNGApprox) is not an effective solution in most cases. When tuned to achieve high search recall (80% or higher), it provides a fairly competitive recommendation performance compared to an efficient exact search method but offers no advantage in terms of efficiency (0.1x—1.5x speedup). Low search recall (<60%) leads to poor recommendation performance. Finally, medium recall values (60%—80%) lead to reasonable recommendation performance but are hard to achieve and offer only a modest gain in efficiency (1.5x—2.3x).

Private approximate nearest neighbor search for on-chain data based on locality-sensitive hashing

Image retrieval or content-based image retrieval (CBIR) can be transformed into the calculation of the distance between image feature vectors. The closer the vectors are, the higher the image similarity will be. In the image retrieval system for large-scale dataset, the approximate nearest-neighbor (ANN) search can quickly obtain the top k images closest to the query image, which is the Top-k problem in the field of information retrieval. With the traditional ANN algorithms, such as KD-Tree, R-Tree, and M-Tree, when the dimension of the image feature vector increases, the computing time will increase exponentially due to the curse of dimensionality. In order to reduce the calculation time and improve the efficiency of image retrieval, we propose an ANN search algorithm based on the Product Quantization Table (PQTable). After quantizing and compressing the image feature vectors by the product quantization algorithm, we can construct the image index structure of the PQTable, which speeds up image retrieval. We also propose a multi-PQTable query strategy for ANN search. Besides, we generate several nearest-neighbor vectors for each sub-compressed vector of the query vector to reduce the failure rate and improve the recall in image retrieval. Through theoretical analysis and experimental verification, it is proved that the multi-PQTable query strategy and the generation of several nearest-neighbor vectors are greatly correct and efficient.

Approximate nearest neighbor search (ANNS) in high-dimensional vector spaces has become increasingly crucial in database and machine learning applications. Most previous ANNS algorithms require TB-scale memory to store indices of billion-scale datasets, making their deployment extremely expensive for high-performance ANNS services. The emerging SmartSSD technology offers an opportunity to achieve scalable ANNS via near data processing (NDP). However, there remain several challenges to directly adopt existing ANNS algorithms on multiple SmartSSDs. In this paper, we present SmartANNS, a SmartSSD-empowered billion-scale ANNS solution based on a hierarchical indexing methodology. We propose several novel designs to achieve near-linear scaling with multiple SmartSSDs. First, we propose a “host CPUs + SmartSSDs” cooperative architecture incorporated with hierarchical indices to significantly reduce data accesses and computations on SmartSSDs. Second, we propose dynamic task scheduling based on optimized data layout to achieve both load balancing and data reusing for multiple SmartSSDs. Third, we further propose a learning-based shard pruning algorithm to eliminate unnecessary computations on SmartSSDs. We implement SmartANNS using Samsung’s commercial SmartSSDs. Experimental results show that SmartANNS can improve query per second (QPS) by up to 10.7 × compared with the state-of-the-art SmartSSD-based ANNS solution–CSDANNS. Moreover, SmartANNS can achieve near-linear performance scalability for large-scale datasets using multiple SmartSSDs.

Vector similarity search (VSS) is crucial in many AI applications, such as few-shot learning (FSL) and approximate nearest-neighbor search (ANNS), but it demands significant memory capacity and incurs substantial energy costs for data transfers during large-scale comparisons. Various in-memory search technologies have been developed to improve energy efficiency, with NAND-based multi-bit content-addressable memory (MCAM) standing out as a promising solution for its high density and large capacity. MCAM can operate in exact-search (ES) mode, supporting only perfect matches with low energy cost, or in approximate-search (AS) mode, enabling flexible VSS. However, AS mode incurs significant energy waste when comparing queries with non-target stored vectors. To address this issue, we propose Hybrid-M, a 3D NAND-based in-memory VSS architecture that integrates both modes into a single hybrid matching process, using ES mode as a filter to reduce redundant searches for AS mode. We apply three techniques to optimize this integration: range encoding for multi-level cells (MLC) to enhance filtering, search voltage shifts to mitigate the impact on AS accuracy and reduce matching currents, and a filtering-aware training method to further improve reliability and energy efficiency. Results show that Hybrid-M achieves comparable accuracy while reducing energy consumption by 67% to 83% compared to MACM-based VSS using only AS mode, across various many-class FSL and ANNS workloads.

We propose a new algorithm for fast approximate nearest neighbor search based on the properties of ordered vectors. Data vectors are classified based on the index and sign of their largest components, thereby partitioning the space in a number of cones centered in the origin. The query is itself classified, and the search starts from the selected cone and proceeds to neighboring ones. Overall, the proposed algorithm corresponds to locality sensitive hashing in the space of directions, with hashing based on the order of components. Thanks to the statistical features emerging through ordering, it deals very well with the challenging case of unstructured data, and is a valuable building block for more complex techniques dealing with structured data. Experiments on both simulated and real-world data prove the proposed algorithm to provide a state-of-the-art performance.

The Iterative Closest Point (ICP) algorithm is one of the most popular methods for geometric alignment of 3-dimensional data points. We focus on how to make it faster for 3D range scanner in intelligent vehicle. The ICP algorithm mainly consists of two parts: nearest neighbor search and estimation of transformation between two data sets. The former is the most time consuming process. Many variants of the k-d trees have been introduced to accelerate the search. This paper presents a remarkably efficient search procedure, exploiting two concepts of approximate nearest neighbor and local search. Consequently, the proposed algorithm is about 24 times faster than the standard k-d tree.

We introduce descriptor-based segmentation that extends existing patch-based methods by combining intensities, features, and location information. Since it is unclear which image features are best suited for patch selection, we perform a broad empirical study on a multitude of different features. We extend nonlocal means segmentation by including image features and location information. We search larger windows with an efficient nearest neighbor search based on kd-trees. We compare a large number of image features. The best results were obtained for entropy image features, which have not yet been used for patch-based segmentation. We further show that searching larger image regions with an approximate nearest neighbor search and location information yields a significant improvement over the bounded nearest neighbor search traditionally employed in patch-based segmentation methods. Features and location information significantly increase the segmentation accuracy. The best features highlight boundaries in the image. Our detailed analysis of several aspects of nonlocal means-based segmentation yields new insights about patch and neighborhood sizes together with the inclusion of location information. The presented approach advances the state-of-the-art in the segmentation of parotid glands for radiation therapy planning.

We present a novel algorithm of exemplar-based image inpainting which can achieve an interactive response and generate results with good quality. In this paper, we modify exemplar-based method with the use of Discrete Cosine Transformation (DCT) for the strategy of exemplar matching. We decompose exemplars by DCT and evaluate the matching score with fewer coefficients, which is unprecedented in image inpainting. The reason why using fewer coefficients is so important is that the efficiency of Approximate Nearest Neighbor (ANN) search drops significantly when using high dimensions. We have also developed a local gradient-based filling algorithm to complete the image blocks with unknown pixels so that the ANN search can be adopted to speed up the matching while preserving the continuity of image. Experimental results prove the advantage of this proposed method.

Spatial sorting: An efficient strategy for approximate nearest neighbor searching

Recently, Approximate Nearest Neighbor (ANN) Search has become a very popular approach for similarity search on large-scale datasets. In this paper, we propose a novel vector quantization method for ANN, which introduces a joint multi-layer K-Means clustering solution for determination of the codebooks. The performance of the proposed method is improved further by a joint encoding scheme. Experimental results verify the success of the proposed algorithm as it outperforms the state-of-the-art methods.

A critical piece of the modern information retrieval puzzle is approximate nearest neighbor search. Its objective is to return a set of k data points that are closest to a query point, with its accuracy measured by the proportion of exact nearest neighbors captured in the returned set. One popular approach to this question is clustering: The indexing algorithm partitions data points into non-overlapping subsets and represents each partition by a point such as its centroid. The query processing algorithm first identifies the nearest clusters---a process known as routing---then performs a nearest neighbor search over those clusters only. In this work, we make a simple observation: The routing function solves a ranking problem. Its quality can therefore be assessed with a ranking metric, making the function amenable to learning-to-rank. Interestingly, ground-truth is often freely available: Given a query distribution in a top-k configuration, the ground-truth is the set of clusters that contain the exact top-k vectors. We develop this insight and apply it to Maximum Inner Product Search (MIPS). As we demonstrate empirically on various datasets, learning a simple linear function consistently improves the accuracy of clustering-based MIPS.