Camera and 3D LiDAR sensors have become indispensable devices in modern autonomous driving vehicles. Camera provides fine-grained texture and color information in 2D space, while LiDAR captures more precise and farther-away distance measurements of the surrounding environments. The complementary information from these two sensors makes the fusion of two modalities a desired option. However, two primary challenges in the fusion of camera and LiDAR hinder its performance, i.e., how to effectively fuse the information from these two modalities and how to precisely align them (suffering from the weak spatiotemporal synchronization problem). This article proposes a coarse-to-fine LiDAR and camera fusion-based network, named LIF-Seg, for LiDAR segmentation. For the first challenge, unlike these previous works fusing the point cloud and image information in a one-to-one manner, the proposed method introduces a simple but effective early-fusion strategy to fully utilize the contextual information of images. Second, to tackle the weak spatiotemporal synchronization problem, an offset rectification approach is designed to align the features of the two modalities. The cooperation of these two components leads to the success of the effective camera-LiDAR fusion. Experimental results on the nuScenes dataset show the superiority of LIF-Seg over existing methods by a large margin. Ablation studies and analyses further illustrate that the LIF-Seg can effectively address the weak spatiotemporal synchronization problem.

Estimating 3D hand shape from a single-view RGB image is important for many applications. However, the diversity of hand shapes and postures, depth ambiguity, and occlusion may result in pose errors and noisy hand meshes. Making full use of 2D cues such as 2D pose can effectively improve the quality of 3D human hand shape estimation. In this paper, we use 2D joint heatmaps to obtain spatial details for robust pose estimation. We also introduce a depth-independent 2D mesh to avoid depth ambiguity in mesh regression for efficient hand-image alignment. Our method has four cascaded stages: 2D cue extraction, pose feature encoding, initial reconstruction, and reconstruction refinement. Specifically, we first encode the image to determine semantic features during 2D cue extraction; this is also used to predict hand joints and for segmentation. Then, during the pose feature encoding stage, we use a hand joints encoder to learn spatial information from the joint heatmaps. Next, a coarse 3D hand mesh and 2D mesh are obtained in the initial reconstruction step; a mesh squeeze-and-excitation block is used to fuse different hand features to enhance perception of 3D hand structures. Finally, a global mesh refinement stage learns non-local relations between vertices of the hand mesh from the predicted 2D mesh, to predict an offset hand mesh to fine-tune the reconstruction results. Quantitative and qualitative results on the FreiHAND benchmark dataset demonstrate that our approach achieves state-of-the-art performance.

In this paper, we propose a novel joint instance and semantic segmentation approach, called JSNet++, to address the instance and semantic segmentation tasks of 3D point clouds simultaneously. We first introduce a basic joint segmentation framework (JSNet). It fuses features from different layers of the backbone network to obtain more discriminative features and makes the two tasks take advantage of each other with a joint instance and semantic segmentation (JISS) module. Specifically, the JISS transforms semantic features into instance embedding space, and then the transformed features are fused with instance features to facilitate instance segmentation. Meanwhile, the JISS module also makes semantic segmentation benefit from instance segmentation by aggregating instance features to semantic feature space. To further reduce the memory consumption of JSNet, we design a dynamic filters for convolution (DFConv) on point clouds. Specifically, we exploit the geometry and density information to generate the dynamic filters, which are used to perform depthwise convolution with the input features. Afterwards, we unify the spatial correlation and channel correlation into a module to fully explore the pointwise correlation in point clouds, and we develop an improved JISS module (JISS*) by using the pointwise correlation module to further improve the accuracy of segmentation. Finally, based on the JSNet, DFConv and JISS*, we propose a new joint segmentation network, termed JSNet++. Experimental results on the benchmarks S3DIS and ScanNet v2 datasets demonstrate the effectiveness of our approach, and our method achieves significant performance improvements over baseline on both instance and semantic segmentation.

In this paper, we propose a novel joint instance and semantic segmentation approach, which is called JSNet, in order to address the instance and semantic segmentation of 3D point clouds simultaneously. Firstly, we build an effective backbone network to extract robust features from the raw point clouds. Secondly, to obtain more discriminative features, a point cloud feature fusion module is proposed to fuse the different layer features of the backbone network. Furthermore, a joint instance semantic segmentation module is developed to transform semantic features into instance embedding space, and then the transformed features are further fused with instance features to facilitate instance segmentation. Meanwhile, this module also aggregates instance features into semantic feature space to promote semantic segmentation. Finally, the instance predictions are generated by applying a simple mean-shift clustering on instance embeddings. As a result, we evaluate the proposed JSNet on a large-scale 3D indoor point cloud dataset S3DIS and a part dataset ShapeNet, and compare it with existing approaches. Experimental results demonstrate our approach outperforms the state-of-the-art method in 3D instance segmentation with a significant improvement in 3D semantic prediction and our method is also beneficial for part segmentation. The source code for this work is available at https://github.com/dlinzhao/JSNet.