CVPR 2024 Papers

Geometry-agnostic system identification is a technique for identifying the geometry and physical properties of an object from video sequences without any geometric assumptions. Recently physics-augmented continuum neural radiance fields (PAC-NeRF) has demonstrated promising results for this technique by utilizing a hybrid Eulerian-Lagrangian representation in which the geometry is represented by the Eulerian grid representations of NeRF the physics is described by a material point method (MPM) and they are connected via Lagrangian particles. However a notable limitation of PAC-NeRF is that its performance is sensitive to the learning of the geometry from the first frames owing to its two-step optimization. First the grid representations are optimized with the first frames of video sequences and then the physical properties are optimized through video sequences utilizing the fixed first-frame grid representations. This limitation can be critical when learning of the geometric structure is difficult for example in a few-shot (sparse view) setting. To overcome this limitation we propose Lagrangian particle optimization (LPO) in which the positions and features of particles are optimized through video sequences in Lagrangian space. This method allows for the optimization of the geometric structure across the entire video sequence within the physical constraints imposed by the MPM. The experimental results demonstrate that the LPO is useful for geometric correction and physical identification in sparse-view settings.

Out-of-distribution (OOD) generalization in the graph domain is challenging due to complex distribution shifts and a lack of environmental contexts. Recent methods attempt to enhance graph OOD generalization by generating flat environments. However such flat environments come with inherent limitations to capture more complex data distributions. Considering the DrugOOD dataset which contains diverse training environments (e.g. scaffold size etc.) flat contexts cannot sufficiently address its high heterogeneity. Thus a new challenge is posed to generate more semantically enriched environments to enhance graph invariant learning for handling distribution shifts. In this paper we propose a novel approach to generate hierarchical semantic environments for each graph. Firstly given an input graph we explicitly extract variant subgraphs from the input graph to generate proxy predictions on local environments. Then stochastic attention mechanisms are employed to re-extract the subgraphs for regenerating global environments in a hierarchical manner. In addition we introduce a new learning objective that guides our model to learn the diversity of environments within the same hierarchy while maintaining consistency across different hierarchies. This approach enables our model to consider the relationships between environments and facilitates robust graph invariant learning. Extensive experiments on real-world graph data have demonstrated the effectiveness of our framework. Particularly in the challenging dataset DrugOOD our method achieves up to 1.29% and 2.83% improvement over the best baselines on IC50 and EC50 prediction tasks respectively.

In this paper we introduce a new perspective for improving image restoration by removing degradation in the textual representations of a given degraded image. Intuitively restoration is much easier on text modality than image one. For example it can be easily conducted by removing degradation-related words while keeping the content-aware words. Hence we combine the advantages of images in detail description and ones of text in degradation removal to perform restoration. To address the cross-modal assistance we propose to map the degraded images into textual representations for removing the degradations and then convert the restored textual representations into a guidance image for assisting image restoration. In particular We ingeniously embed an image-to-text mapper and text restoration module into CLIP-equipped text-to-image models to generate the guidance. Then we adopt a simple coarse-to-fine approach to dynamically inject multi-scale information from guidance to image restoration networks. Extensive experiments are conducted on various image restoration tasks including deblurring dehazing deraining and denoising and all-in-one image restoration. The results showcase that our method outperforms state-of-the-art ones across all these tasks. The codes and models are available at https://github.com/mrluin/TextualDegRemoval.

Graph Contrastive Learning (GCL) a Self-Supervised Learning (SSL) architecture tailored for graphs has shown notable potential for mitigating label scarcity. Its core idea is to amplify feature similarities between the positive sample pairs and reduce them between the negative sample pairs. Unfortunately most existing GCLs consistently present suboptimal performances on both homophilic and heterophilic graphs. This is primarily attributed to two limitations of positive sampling that is incomplete local sampling and blind sampling. To address these limitations this paper introduces a novel GCL framework with an adaptive positive sampling module named grapH contrastivE Adaptive posiTive Samples (HEATS). Motivated by the observation that the affinity matrix corresponding to optimal positive sample sets has a block-diagonal structure with equal weights within each block a self-expressive learning objective incorporating the block and idempotent constraint is presented. This learning objective and the contrastive learning objective are iteratively optimized to improve the adaptability and robustness of HEATS. Extensive experiments on graphs and images validate the effectiveness and generality of HEATS.

Generalized Zero-Shot Learning (GZSL) methods often assume that the unseen classes are similar to seen classes and thus perform poor when unseen classes are dissimilar to seen classes. Although some existing GZSL approaches can alleviate this issue by leveraging additional semantic information from test unseen classes their generalization ability to dissimilar unseen classes is still unsatisfactory. This motivates us to study GZSL in the more practical setting where unseen classes can be either similar or dissimilar to seen classes. In this paper we propose a simple yet effective GZSL framework by exploring diverse semantics from external class names (DSECN) which is simultaneously robust on the similar and dissimilar unseen classes. This is achieved by introducing diverse semantics from external class names and aligning the introduced semantics to visual space using the classification head of pre-trained network. Furthermore we show that the design idea of DSECN can easily be integrate into other advanced GZSL approaches such as the generative-based ones and enhance their robustness for dissimilar unseen classes. Extensive experiments in the practical setting including both similar and dissimilar unseen classes show that our method significantly outperforms the state-of-the-art approaches on all datasets and can be trained very efficiently.

Learned reweighting (LRW) approaches to supervised learning use an optimization criterion to assign weights for training instances in order to maximize performance on a representative validation dataset. We pose and formalize the problem of optimized selection of the validation set used in LRW training to improve classifier generalization. In particular we show that using hard-to-classify instances in the validation set has both a theoretical connection to and strong empirical evidence of generalization. We provide an efficient algorithm for training this meta-optimized model as well as a simple train-twice heuristic for careful comparative study. We demonstrate that LRW with easy validation data performs consistently worse than LRW with hard validation data establishing the validity of our meta-optimization problem. Our proposed algorithm outperforms a wide range of baselines on a range of datasets and domain shift challenges (Imagenet-1K CIFAR-100 Clothing-1M CAMELYON WILDS etc.) with 1% gains using VIT-B on Imagenet. We also show that using naturally hard examples for validation (Imagenet-R / Imagenet-A) in LRW training for Imagenet improves performance on both clean and naturally hard test instances by 1-2%. Secondary analyses show that using hard validation data in an LRW framework improves margins on test data hinting at the mechanism underlying our empirical gains. We believe this work opens up new research directions for the meta-optimization of meta-learning in a supervised learning context.

Improving the detection of distant 3d objects is an important yet challenging task. For camera-based 3D perception the annotation of 3d bounding relies heavily on LiDAR for accurate depth information. As such the distance of annotation is often limited due to the sparsity of LiDAR points on distant objects which hampers the capability of existing detectors for long-range scenarios. We address this challenge by considering only 2D box supervision for distant objects since they are easy to annotate. We propose LR3D a framework that learns to recover the missing depth of distant objects. LR3D adopts an implicit projection head to learn the generation of mapping between 2D boxes and depth using the 3D supervision on close objects. This mapping allows the depth estimation of distant objects conditioned on their 2D boxes making long-range 3D detection with 2D supervision feasible. Experiments show that without distant 3D annotations LR3D allows camera-based methods to detect distant objects (over 200m) with comparable accuracy to full 3D supervision. Our framework is general and could widely benefit 3D detection methods to a large extent.

The encoder-decoder network (ED-Net) is a commonly employed choice for existing depth completion methods but its working mechanism is ambiguous. In this paper we visualize the internal feature maps to analyze how the network densifies the input sparse depth. We find that the encoder feature of ED-Net focus on the areas with input depth points around. To obtain a dense feature and thus estimate complete depth the decoder feature tends to complement and enhance the encoder feature by skip-connection to make the fused encoder-decoder feature dense resulting in the decoder feature also exhibits sparse. However ED-Net obtains the sparse decoder feature from the dense fused feature at the previous stage where the "dense to sparse" process destroys the completeness of features and loses information. To address this issue we present a depth feature upsampling network (DFU) that explicitly utilizes these dense features to guide the upsampling of a low-resolution (LR) depth feature to a high-resolution (HR) one. The completeness of features is maintained throughout the upsampling process thus avoiding information loss. Furthermore we propose a confidence-aware guidance module (CGM) which is confidence-aware and performs guidance with adaptive receptive fields (GARF) to fully exploit the potential of these dense features as guidance. Experimental results show that our DFU a plug-and-play module can significantly improve the performance of existing ED-Net based methods with limited computational overheads and new SOTA results are achieved. Besides the generalization capability on sparser depth is also enhanced. Project page: https://npucvr.github.io/DFU.

Semantic segmentation in bird's eye view (BEV) plays a crucial role in autonomous driving. Previous methods usually follow an end-to-end pipeline directly predicting the BEV segmentation map from monocular RGB inputs. However the challenge arises when the RGB inputs and BEV targets from distinct perspectives making the direct point-to-point predicting hard to optimize. In this paper we decompose the original BEV segmentation task into two stages namely BEV map reconstruction and RGB-BEV feature alignment. In the first stage we train a BEV autoencoder to reconstruct the BEV segmentation maps given corrupted noisy latent representation which urges the decoder to learn fundamental knowledge of typical BEV patterns. The second stage involves mapping RGB input images into the BEV latent space of the first stage directly optimizing the correlations between the two views at the feature level. Our approach simplifies the complexity of combining perception and generation into distinct steps equipping the model to handle intricate and challenging scenes effectively. Besides we propose to transform the BEV segmentation map from the Cartesian to the polar coordinate system to establish the column-wise correspondence between RGB images and BEV maps. Moreover our method requires neither multi-scale features nor camera intrinsic parameters for depth estimation and saves computational overhead. Extensive experiments on nuScenes and Argoverse show the effectiveness and efficiency of our method. Code is available at https://github.com/happytianhao/TaDe.

The zero-shot performance of existing vision-language models (VLMs) such as CLIP is limited by the availability of large-scale aligned image and text datasets in specific domains. In this work we leverage two complementary sources of information -- descriptions of categories generated by large language models (LLMs) and abundant fine-grained image classification datasets -- to improve the zero-shot classification performance of VLMs across fine-grained domains. On the technical side we develop methods to train VLMs with this "bag-level" image-text supervision. We find that simply using these attributes at test-time does not improve performance but our training strategy for example on the iNaturalist dataset leads to an average improvement of 4-5% in zero-shot classification accuracy for novel categories of birds and flowers. Similar improvements are observed in domains where a subset of the categories was used to fine-tune the model. By prompting LLMs in various ways we generate descriptions that capture visual appearance habitat and geographic regions and pair them with existing attributes such as the taxonomic structure of the categories. We systematically evaluate their ability to improve zero-shot categorization in natural domains. Our findings suggest that geographic priors can be just as effective and are complementary to visual appearance. Our method also outperforms prior work on prompt-based tuning of VLMs. We release the benchmark consisting of 14 datasets at https://github.com/cvl-umass/AdaptCLIPZS which will contribute to future research in zero-shot recognition.

Vision-and-language models trained to match images with text can be combined with visual explanation methods to point to the locations of specific objects in an image. Our work shows that the localization --"grounding'"-- abilities of these models can be further improved by finetuning for self-consistent visual explanations. We propose a strategy for augmenting existing text-image datasets with paraphrases using a large language model and SelfEQ a weakly-supervised strategy on visual explanation maps for paraphrases that encourages self-consistency. Specifically for an input textual phrase we attempt to generate a paraphrase and finetune the model so that the phrase and paraphrase map to the same region in the image. We posit that this both expands the vocabulary that the model is able to handle and improves the quality of the object locations highlighted by gradient-based visual explanation methods (e.g. GradCAM). We demonstrate that SelfEQ improves performance on Flickr30k ReferIt and RefCOCO+ over a strong baseline method and several prior works. Particularly comparing to other methods that do not use any type of box annotations we obtain 84.07% on Flickr30k (an absolute improvement of 4.69%) 67.40% on ReferIt (an absolute improvement of 7.68%) and 75.10% 55.49% on RefCOCO+ test sets A and B respectively (an absolute improvement of 3.74% on average).

Test-time adaptation (TTA) is a technique to improve the performance of a pre-trained source model on a target distribution without using any labeled data. However existing self-trained TTA methods often face the challenges of unreliable pseudo-labels and unstable model optimization. In this paper we propose an Improved Self-Training (IST) approach which addresses these challenges by enhancing the pseudo-label quality and stabilizing the adaptation process. Specifically we use a simple augmentation strategy to generate multiple views of each test sample and construct a graph structure to correct the pseudo-labels based on the similarity of the latent features. Moreover we adopt a parameter moving average scheme to smooth the model updates and prevent catastrophic forgetting. Instead of using a model with fixed label space we explore the adaptability of the foundation model CLIP to various downstream tasks at test time. Extensive experiments on various benchmarks show that IST can achieve significant and consistent improvements over the existing TTA methods in classification detection and segmentation tasks.

Implicit Neural Representation (INR) as a mighty representation paradigm has achieved success in various computer vision tasks recently. Due to the low-frequency bias issue of vanilla multi-layer perceptron (MLP) existing methods have investigated advanced techniques such as positional encoding and periodic activation function to improve the accuracy of INR. In this paper we connect the network training bias with the reparameterization technique and theoretically prove that weight reparameterization could provide us a chance to alleviate the spectral bias of MLP. Based on our theoretical analysis we propose a Fourier reparameterization method which learns coefficient matrix of fixed Fourier bases to compose the weights of MLP. We evaluate the proposed Fourier reparameterization method on different INR tasks with various MLP architectures including vanilla MLP MLP with positional encoding and MLP with advanced activation function etc. The superiority approximation results on different MLP architectures clearly validate the advantage of our proposed method. Armed with our Fourier reparameterization method better INR with more textures and less artifacts can be learned from the training data. The codes are available at https://github.com/LabShuHangGU/FR-INR.

Recent advancements in video modeling extensively rely on optical flow to represent the relationships across frames but this approach often lacks efficiency and fails to model the probability of the intrinsic motion of objects. In addition conventional encoder-decoder frameworks in video processing focus on modeling the correlation in the encoder leading to limited generative capabilities and redundant intermediate representations. To address these challenges this paper proposes a novel Implicit Motion Function (IMF) method. Our approach utilizes a low-dimensional latent token as the implicit representation along with the use of cross-attention to implicitly model the correlation between frames. This enables the implicit modeling of temporal correlations and understanding of object motions. Our method not only improves sparsity and efficiency in representation but also explores the generative capabilities of the decoder by integrating correlation modeling within it. The IMF framework facilitates video editing and other generative tasks by allowing the direct manipulation of latent tokens. We validate the effectiveness of IMF through extensive experiments on multiple video tasks demonstrating superior performance in terms of reconstructed video quality compression efficiency and generation ability.

Visible-Infrared Person Re-identification (VI-ReID) is a challenging cross-modal pedestrian retrieval task due to significant intra-class variations and cross-modal discrepancies among different cameras. Existing works mainly focus on embedding images of different modalities into a unified space to mine modality-shared features. They only seek distinctive information within these shared features while ignoring the identity-aware useful information that is implicit in the modality-specific features. To address this issue we propose a novel Implicit Discriminative Knowledge Learning (IDKL) network to uncover and leverage the implicit discriminative information contained within the modality-specific. First we extract modality-specific and modality-shared features using a novel dual-stream network. Then the modality-specific features undergo purification to reduce their modality style discrepancies while preserving identity-aware discriminative knowledge. Subsequently this kind of implicit knowledge is distilled into the modality-shared feature to enhance its distinctiveness. Finally an alignment loss is proposed to minimize modality discrepancy on enhanced modality-shared features. Extensive experiments on multiple public datasets demonstrate the superiority of IDKL network over the state-of-the-art methods.

The Object Goal navigation (ObjectNav) task requires the agent to navigate to a specified target in an unseen environment. Since the environment layout is unknown the agent needs to infer the unknown contextual objects from partially observations thereby deducing the likely location of the target. Previous end-to-end RL methods capture contextual relationships through implicit representations while they lack notion of geometry. Alternatively modular methods construct local maps for recording the observed geometric structure of unseen environment however lacking the reasoning of contextual relation limits the exploration efficiency. In this work we propose the self-supervised generative map (SGM) a modular method that learns the explicit context relation via self-supervised learning. The SGM is trained to leverage both episodic observations and general knowledge to reconstruct the masked pixels of a cropped global map. During navigation the agent maintains an incomplete local semantic map meanwhile the unknown regions of the local map are generated by the pre-trained SGM. Based on the generated map the agent sets the predicted location of the target as the goal and moves towards it. Experiments on Gibson MP3D and HM3D show the effectiveness of our method.

Open-vocabulary semantic segmentation (OVS) aims to segment images of arbitrary categories specified by class labels or captions. However most previous best-performing methods whether pixel grouping methods or region recognition methods suffer from false matches between image features and category labels. We attribute this to the natural gap between the textual features and visual features. In this work we rethink how to mitigate false matches from the perspective of image-to-image matching and propose a novel relation-aware intra-modal matching (RIM) framework for OVS based on visual foundation models. RIM achieves robust region classification by firstly constructing diverse image-modal reference features and then matching them with region features based on relation-aware ranking distribution. The proposed RIM enjoys several merits. First the intra-modal reference features are better aligned circumventing potential ambiguities that may arise in cross-modal matching. Second the ranking-based matching process harnesses the structure information implicit in the inter-class relationships making it more robust than comparing individually. Extensive experiments on three benchmarks demonstrate that RIM outperforms previous state-of-the-art methods by large margins obtaining a lead of more than 10% in mIoU on PASCAL VOC benchmark

This paper addresses text-supervised semantic segmentation aiming to learn a model capable of segmenting arbitrary visual concepts within images by using only image-text pairs without dense annotations. Existing methods have demonstrated that contrastive learning on image-text pairs effectively aligns visual segments with the meanings of texts. We notice that there is a discrepancy between text alignment and semantic segmentation: A text often consists of multiple semantic concepts whereas semantic segmentation strives to create semantically homogeneous segments. To address this issue we propose a novel framework Image-Text Co-Decomposition (CoDe) where the paired image and text are jointly decomposed into a set of image regions and a set of word segments respectively and contrastive learning is developed to enforce region-word alignment. To work with a vision-language model we present a prompt learning mechanism that derives an extra representation to highlight an image segment or a word segment of interest with which more effective features can be extracted from that segment. Comprehensive experimental results demonstrate that our method performs favorably against existing text-supervised semantic segmentation methods on six benchmark datasets.

We present Image Sculpting a new framework for editing 2D images by incorporating tools from 3D geometry and graphics. This approach differs markedly from existing methods which are confined to 2D spaces and typically rely on textual instructions leading to ambiguity and limited control. Image Sculpting converts 2D objects into 3D enabling direct interaction with their 3D geometry. Post-editing these objects are re-rendered into 2D merging into the original image to produce high-fidelity results through a coarse-to-fine enhancement process. The framework supports precise quantifiable and physically-plausible editing options such as pose editing rotation translation 3D composition carving and serial addition. It marks an initial step towards combining the creative freedom of generative models with the precision of graphics pipelines.