Open-CHOIR: Contact-aware 4D Hand-Object Interaction Reconstruction

We ask whether everyday open-world monocular videos can be turned into reusable 4D interaction primitives: articulated hand motion, object shape with 6D pose over time, and the when/where of contact. Such a capability would enable scalable mining of real interactions and, beyond reconstruction, support scene-aware synthesis and planning. However, reconstructing hand-object interaction (HOI) from challenging monocular videos remains difficult: methods often assume known objects or curated scenes, and separately estimated hands and objects easily become misaligned under clutter, occlusion, and unseen object geometries. Targeting this setting, we present Open-CHOIR, an Open-world Contact-aware HOI Reconstruction framework for a monocular camera, using contact as an explicit coupling signal between hands and objects. Open-CHOIR first initializes a coarse, contact-agnostic 4D HOI sequence from open-world visual priors. It then introduces a generative HOI spatial rectification module to predict ray-depth corrections and rectify hand-object relative placement, then derives initial per-frame contact correspondences on the rectified geometry. Last, a contact-aware joint optimization with dynamically updated contact constraints enforces geometric, temporal, and contact consistency. Experiments on controlled and challenging videos show that Open-CHOIR improves object reconstruction, physical plausibility, and temporal consistency over state-of-the-art methods.

Contributions

An open-world monocular 4D HOI reconstruction method that extracts 2D interaction cues, performs guarded object tracking, and produces a coarse contact-agnostic sequence.
A generative HOI spatial rectification module that predicts ray-depth corrections before constructing initial per-frame barycentric contact correspondences.
A contact-aware joint optimization with dynamically updated contact constraints, validated on controlled and in-the-wild videos.

Method Overview

Stage 1 coarse 4D HOI initialization — From a monocular video, we first obtain 2D HOI cues and initialize 3D hand and object reconstructions to form isolated sequences.

Stage 2 generative HOI spatial rectification — A flow-matching generative HOI spatial rectification module rectifies hand-object relative placement before initial contact correspondence construction.

Stage 3 hierarchical contact-aware optimization — Contact-aware optimization refines the sequence across phases, yielding physically consistent 4D HOI sequences.

Our Representative Examples

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Explore representative sequences with synchronized input video, reconstructed 4D geometry, and rest-pose contact predictions. Click on the above arrows to browse different representative examples.

Qualitative Comparison with SOTA Methods

More Qualitative Results of Our Method

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Bimanual Cases

Our method generalizes to challenging bimanual scenarios — two-hand two-object and two-hand one-object hand–object interaction. Drag the 3D viewer to explore the reconstruction from any angle.

BibTeX

@article{openchoir2026,
  title     = {Open-CHOIR: Contact-aware 4D Hand-Object Interaction Reconstruction},
  author    = {Xu, Hao and Liu, Yilin and Wang, Yinqiao and Fu, Chi-Wing and Mitra, Niloy J.},
  journal   = {ACM Transactions on Graphics},
  volume    = {45},
  number    = {6},
  year      = {2026},
  publisher = {Association for Computing Machinery},
  note      = {Presented at SIGGRAPH Asia 2026}
}