🎯 DARTS: Diffusion Approximated Residual Time Sampling for Time-of-flight Rendering in Homogeneous Scattering Media

Qianyue He, Dongyu Du, Haitian Jiang, Xin Jin*
Tsinghua Shenzhen International Graduate School
ACM Transactions on Graphics (SIGGRAPH Asia 2024 Journal Track)
*Indicates Corresponding Author
Paper Code arXiv

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Fast forward show-casing of our DARTS method. We present a simple alphabet scene, with different BSDFs for the geometries and thin homogeneous scattering medium. Rendering outputs and FLIP loss results are given, side-by-side.

Abstract

Time-of-flight (ToF) devices have greatly propelled the advancement of various multi-modal perception applications. However, achieving accurate rendering of time-resolved information remains a challenge, particularly in scenes involving complex geometries, diverse materials and participating media. Existing ToF rendering works have demonstrated notable results, yet they struggle with scenes involving scattering media and camera-warped settings. Other steady-state volumetric rendering methods exhibit significant bias or variance when directly applied to ToF rendering tasks. To address these challenges, we integrate transient diffusion theory into path construction and propose novel sampling methods for free-path distance and scattering direction, via resampled importance sampling and offline tabulation. An elliptical sampling method is further adapted to provide controllable vertex connection satisfying any required photon traversal time. In contrast to the existing temporal uniform sampling strategy, our method is the first to consider the contribution of transient radiance to importance-sample the full path, and thus enables improved temporal path construction under multiple scattering settings. The proposed method can be integrated into both path tracing and photon-based frameworks, delivering significant improvements in quality and efficiency with at least a 5x MSE reduction versus SOTA methods in equal rendering time.

Method Overview

Method Flow Chart

In this paper, we propose a diffusion approximated residual time sampling method (DARTS, for short), which provides full transient path construction and effective vertex connection within complex volumetric scenes and under camera-warped settings. To address the challenge of constructing effective temporal sampling paths in scattering media, instead of adopting uniform sampling in the time domain, which overlooks the radiance contribution differences of different path samples, we perform importance sampling on the transient radiance by integrating the transient diffusion approximation (DA) into the rendering process. This approach allows us to obtain improved free-path distance and direction samples with enhanced overall radiance, leading to better convergence performance. To impose path time constraints, we extend the ellipsoidal connection method and further combine it with the proposed DA-based direction sampling to bypass challenges introduced by the reparameterization of ellipsoidal connection and avoid sampling inefficiency in camera-warped settings. The proposed method is inherently unbiased and introduces negligible extra memory overhead compared to the naive methods.

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Cite

To cite this work, you can use the following BibTex code: 
        
        @article{he2024darts,
          title={DARTS: Diffusion Approximated Residual Time Sampling for Time-of-flight Rendering in Homogeneous Scattering Media},
          author={He, Qianyue and Du, Dongyu and Jiang, Haitian and Jin, Xin},
          journal={ACM Transactions on Graphics (TOG)},
          volume={43},
          number={6},
          pages={1--14},
          year={2024},
          publisher={ACM New York, NY, USA}
        }
GB/T 7714: He Q, Du D, Jiang H, et al. DARTS: Diffusion Approximated Residual Time Sampling for Time-of-flight Rendering in Homogeneous Scattering Media[J]. ACM Transactions on Graphics (TOG), 2024, 43(6): 1-14.
MLA: He, Qianyue, et al. "DARTS: Diffusion Approximated Residual Time Sampling for Time-of-flight Rendering in Homogeneous Scattering Media." ACM Transactions on Graphics (TOG) 43.6 (2024): 1-14.