Neural Radiance Fields (NeRF) has emerged as a compelling framework for scene representation and 3D recovery. To improve its performance on real-world data, depth regularizations have proven to be the most effective ones. However, depth estimation models not only require expensive 3D supervision in training, but also suffer from generalization issues. As a result, the depth estimations can be erroneous in practice, especially for outdoor unbounded scenes. In this paper, we propose to employ view-consistent distributions instead of fixed depth value estimations to regularize NeRF training. Specifically, the distribution is computed by utilizing both low-level color features and high-level distilled features from foundation models at the projected 2D pixel-locations from per-ray sampled 3D points. By sampling from the view-consistency distributions, an implicit regularization is imposed on the training of NeRF. We also utilize a depth-pushing loss that works in conjunction with the sampling technique to jointly provide effective regularizations for eliminating the failure modes. Extensive experiments conducted on various scenes from public datasets demonstrate that our proposed method can generate significantly better novel view synthesis results than state-of-the-art NeRF variants as well as different depth regularization methods.

Seeking reliable correspondences then recovering camera poses from a set of putative correspondences extracted from two images of the same scene is a fundamental problem in computer vision. Recent advances have demonstrated that this problem can be effectively solved by using a deep architecture based on the multi-layer perceptron, where the context normalization is designed to make the network permutation-equivariant and embed global information in the sparse point data. However, the context normalization simply normalizes the feature maps according to their distribution and treats each correspondence equally, leading to difficulties in adequately capturing scene geometry encoded by the inliers, especially in case of severe outliers. To address this issue, this paper designs a context-sensitive network based on the self-attention mechanism, termed as correspondence attention transformer (CAT), to enhance the consistent geometry information of inliers and simultaneously suppress outliers during embedding global information. In particular, we design an attention-style structure to aggregate features from all correspondences, i.e., a spatial attention namely CAT-S, which provides each correspondence with information exchange from others in the putative set. To capture the contextual information in a more comprehensive and robust way, we also introduce a multi-head mechanism in our structure to exploit the geometrical context from different aspects. Moreover, considering the high memory request in spatial attention, we propose a covariance normalized channel attention CAT-C in our framework, which can largely reduce the memory consumption and parameter scale, but it asks for eigenvalue decomposition in each attention block thus resulting in more runtime. Anyway, these two attention mechanisms can realize information exchange from the spatial or channel aspect, which both contribute to constructing the geometrical context between inliers and encourage the network to pay more attention to the feature subset about potential inliers. Extensive experiments have been conducted over both indoor and outdoor datasets on the tasks of camera pose estimation, outlier removal, and image registration, which demonstrate the superiority of our method that realizes a large performance improvement compared with the current state-of-the-art approaches.

For robust feature matching, a popular and particularly effective method is to recover smooth functions from the data to differentiate the true correspondences (inliers) from false correspondences (outliers). In the existing works, the well-established regularization theory has been extensively studied and exploited to estimate the functions while controlling its complexity to enforce the smoothness constraint, which has shown prominent advantages in this task. However, despite the theoretical optimality properties, the high complexities in both time and space are induced and become the main obstacle of their application. In this article, we propose a novel method for multivariate regression and point matching, which exploits the sparsity structure of smooth functions. Specifically, we use compact Fourier bases for constructing the function, which inherently allows a coarse-to-fine representation. The smoothness constraint can be explicitly imposed by adopting a few low-frequency bases for representation, resulting in reduced computational complexities of the induced multivariate regression algorithm. To cope with potential gross outliers, we formulate the learning problem into a Bayesian framework with latent variables indicating the inliers and outliers and a mixture model accounting for the distribution of data, where a fast expectation-maximization solution can be derived. Extensive experiments are conducted on synthetic data and real-world image matching, and point set registration datasets, which demonstrates the advantages of our method against the current state-of-the-art methods in terms of both scalability and robustness.

In this paper, we explore a new type of extrinsic method to directly align two geometric shapes with point-to-point correspondences in ambient space by recovering a deformation, which allows more continuous and smooth maps to be obtained. Specifically, the classic coherent point drift is revisited and generalizations have been proposed. First, by observing that the deformation model is essentially defined with respect to Euclidean space, we generalize the kernel method to non-Euclidean domains. This generally leads to better results for processing shapes, which are known as two-dimensional manifolds. Second, a generalized probabilistic model is proposed to address the sensibility of coherent point drift method to local optima. Instead of directly optimizing over the objective of coherent point drift, the new model allows to focus on a group of most confident ones, thus improves the robustness of the registration system. Experiments are conducted on multiple public datasets with comparison to state-of-the-art competitors, demonstrating the superiority of our method which is both flexible and efficient to improve the matching accuracy due to our extrinsic alignment objective in ambient space.

Geometric model fitting is a fundamental task in computer vision, which serves as the pre-requisite of many downstream applications. While the problem has a simple intrinsic structure where the solution can be parameterized within a few degrees of freedom, the ubiquitously existing outliers are the main challenge. In previous studies, random sampling techniques have been established as the practical choice, since optimization-based methods are usually too time-demanding. This prospective study is intended to design efficient algorithms that benefit from a general optimization-based view. In particular, two important types of loss functions are discussed, \emph{i.e.} truncated and$l_1$losses, and efficient solvers have been derived for both upon specific approximations. Based on this philosophy, a class of algorithms are introduced to perform deterministic search for the inliers or geometric model. Recommendations are made based on theoretical and experimental analyses. Compared with the existing solutions, the proposed methods are both simple in computation and robust to outliers. Extensive experiments are conducted on publicly available datasets for geometric estimation, which demonstrate the superiority of our methods compared with the state-of-the-art ones. Additionally, we apply our method to the recent benchmark for wide-baseline stereo evaluation, leading to a significant improvement of performance.

Abstract As a fundamental and critical task in various visual applications, image matching can identify then correspond the same or similar structure/content from two or more images. Over the past decades, growing amount and diversity of methods have been proposed for image matching, particularly with the development of deep learning techniques over the recent years. However, it may leave several open questions about which method would be a suitable choice for specific applications with respect to different scenarios and task requirements and how to design better image matching methods with superior performance in accuracy, robustness and efficiency. This encourages us to conduct a comprehensive and systematic review and analysis for those classical and latest techniques. Following the feature-based image matching pipeline, we first introduce feature detection, description, and matching techniques from handcrafted methods to trainable ones and provide an analysis of the development of these methods in theory and practice. Secondly, we briefly introduce several typical image matching-based applications for a comprehensive understanding of the significance of image matching. In addition, we also provide a comprehensive and objective comparison of these classical and latest techniques through extensive experiments on representative datasets. Finally, we conclude with the current status of image matching technologies and deliver insightful discussions and prospects for future works. This survey can serve as a reference for (but not limited to) researchers and engineers in image matching and related fields.

As a fundamental and critical task in feature-based remote sensing image registration, feature matching refers to establishing reliable point correspondences from two images of the same scene. In this article, we propose a simple yet efficient method termed linear adaptive filtering (LAF) for both rigid and nonrigid feature matching of remote sensing images and apply it to the image registration task. Our algorithm starts with establishing putative feature correspondences based on local descriptors and then focuses on removing outliers using geometrical consistency priori together with filtering and denoising theory. Specifically, we first grid the correspondence space into several nonoverlapping cells and calculate a typical motion vector for each one. Subsequently, we remove false matches by checking the consistency between each putative match and the typical motion vector in the corresponding cell, which is achieved by a Gaussian kernel convolution operation. By refining the typical motion vector in an iterative manner, we further introduce a progressive strategy based on the coarse-to-fine theory to promote the matching accuracy gradually. In addition, an adaptive parameter setting strategy and posterior probability estimation based on the expectation-maximization algorithm enhance the robustness of our method to different data. Most importantly, our method is quite efficient where the gridding strategy enables it to achieve linear time complexity. Consequently, some sparse point-based tasks may inspire from our method when they are achieved by deep learning techniques. Extensive feature matching and image registration experiments on several remote sensing data sets demonstrate the superiority of our approach over the state of the art.

As a fundamental and important task in many applications of remote sensing and photogrammetry, feature matching tries to seek correspondences between the two feature sets extracted from an image pair of the same object or scene. This paper focuses on eliminating mismatches from a set of putative feature correspondences constructed according to the similarity of existing well-designed feature descriptors. Considering the stable local topological relationship of the potential true correspondences, we propose a simple yet efficient method named multiscale Top K Rank Preservation (mTopKRP) for robust feature matching. To this end, we first search the K-nearest neighbors of each feature point and generate a ranking list accordingly. Then we design a metric based on the weighted Spearman's footrule distance to describe the similarity of two ranking lists specifically for the matching problem. We build a mathematical optimization model and derive its closed-form solution, enabling our method to establish reliable correspondences in linearithmic time complexity, which requires only tens of milliseconds to handle over 1000 putative matches. We also introduce a multiscale strategy for neighborhood construction, which increases the robustness of our method and can deal with different types of degradation, even when the image pair suffers from a large scale change, rotation, nonrigid deformation, or a large number of mismatches. Extensive experiments on several representative remote sensing image data sets demonstrate the superiority of our method over state of the art.