Detector-Free Structure from Motion

We propose a new structure-from-motion framework to recover accurate camera poses and point clouds from unordered images. Traditional SfM systems typically rely on the successful detection of repeatable keypoints across multiple views as the first step, which is difficult for texture-poor scenes, and poor keypoint detection may break down the whole SfM system. We propose a new detector-free SfM framework to draw benefits from the recent success of detector-free matchers to avoid the early determination of keypoints, while solving the multi-view inconsistency issue of detector-free matchers. Specifically, our framework first reconstructs a coarse SfM model from quantized detector-free matches. Then, it refines the model by a novel iterative refinement pipeline, which iterates between an attention-based multi-view matching module to refine feature tracks and a geometry refinement module to improve the reconstruction accuracy. Experiments demonstrate that the proposed framework outperforms existing detector-based SfM systems on common benchmark datasets. We also collect a texture-poor SfM dataset to demonstrate the capability of our framework to reconstruct texture-poor scenes. Based on this framework, we take $\textit{first place}$ in Image Matching Challenge 2023.Comment: Project page: https://zju3dv.github.io/DetectorFreeSfM

4K4D: Real-Time 4D View Synthesis at 4K Resolution

This paper targets high-fidelity and real-time view synthesis of dynamic 3D scenes at 4K resolution. Recently, some methods on dynamic view synthesis have shown impressive rendering quality. However, their speed is still limited when rendering high-resolution images. To overcome this problem, we propose 4K4D, a 4D point cloud representation that supports hardware rasterization and enables unprecedented rendering speed. Our representation is built on a 4D feature grid so that the points are naturally regularized and can be robustly optimized. In addition, we design a novel hybrid appearance model that significantly boosts the rendering quality while preserving efficiency. Moreover, we develop a differentiable depth peeling algorithm to effectively learn the proposed model from RGB videos. Experiments show that our representation can be rendered at over 400 FPS on the DNA-Rendering dataset at 1080p resolution and 80 FPS on the ENeRF-Outdoor dataset at 4K resolution using an RTX 4090 GPU, which is 30x faster than previous methods and achieves the state-of-the-art rendering quality. Our project page is available at https://zju3dv.github.io/4k4d/.Comment: Project Page: https://zju3dv.github.io/4k4

Enhancement effect of bimetallic amide K2Mn(NH2)4 and in-situ formed KH and Mn4N on the dehydrogenation/hydrogenation properties of Li–Mg–N–H system

In this work, we investigated the influence of the K2Mn(NH2)4 additive on the hydrogen sorption properties of the Mg(NH2)2 + 2LiH (Li–Mg–N–H) system. The addition of 5 mol% of K2Mn(NH2)4 to the Li–Mg–N–H system leads to a decrease of the dehydrogenation peak temperature from 200 ◦C to 172 ◦C compared to the pristine sample. This sample exhibits a constant hydrogen storage capacity of 4.2 wt.% over 25 dehydrogenation/rehydrogenation cycles. Besides that, the in-situ synchrotron powder X-ray diffraction analysis performed on the as prepared Mg(NH2)2 + 2LiH containing K2Mn(NH2)4 indicates the presence of Mn4N. However, no crystalline K-containing phases were detected. Upon dehydrogenation, the formation of KH is observed. The presence of KH and Mn4N positively influences the hydrogen sorption properties of this system, especially at the later stage of rehydrogenation. Under the applied conditions, hydrogenation of the last 1 wt.% takes place in only 2 min. This feature is preserved in the following three cycles.Fil: Gizer, Gökhan. Helmholtz zentrum Geesthacht; AlemaniaFil: Cao, Hujun. Helmholtz zentrum Geesthacht; Alemania. Chinese Academy of Sciences; República de ChinaFil: Puszkiel, Julián Atilio. Helmholtz zentrum Geesthacht; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Pistidda, Claudio. Helmholtz zentrum Geesthacht; AlemaniaFil: Santoru, Antonio. Helmholtz zentrum Geesthacht; AlemaniaFil: Zhang, Weijin. Chinese Academy of Sciences; República de ChinaFil: He, Teng. Chinese Academy of Sciences; República de ChinaFil: Chen, Ping. Chinese Academy of Sciences; República de ChinaFil: Klassen, Thomas. Helmholtz zentrum Geesthacht; Alemania. Helmut Schmidt Universität; ArgentinaFil: Dornheim, Martin. Helmholtz zentrum Geesthacht; Alemani