# Real-time Subsurface Control Variates: Temporally Stable Adaptive Sampling

Proc. ACM Comput. Graph. Interact. Tech. 4, 1 (I3D, 2021)
University of Maryland, Baltimore County
University of Maryland, Baltimore County
Figure 1: Dynamic subsurface scene just after light has been turned off. Our method has consistently lower sample count (d) than SPVG [Xie et al. 2020] (c) at this frame. It leads to lower sampling pass time in dynamic lighting from 12.9 ms to 5.2 ms at 3360 × 1440 (×2.5), while maintaining good quality (47.5 dB) vs SPVG (48.6 dB). Separable (b) runs fastest for the whole subsurface pass at 4.0 ms, however, with visible banding artifacts.

Abstract: Real-time adaptive sampling is a new technique recently proposed for efficient importance sampling in real-time Monte Carlo sampling in subsurface scattering. It adaptively places samples based on variance tracking to help escape the uncanny valley of subsurface rendering. However, the occasional performance drop due to temporal lighting dynamics (e.g., guns or lights turning on and off) could hinder adoption in games or other applications where smooth high frame rate is preferred. In this paper we propose a novel usage of Control Variates (CV) in the sample domain instead of shading domain to maintain a consistent low pass time. Our algorithm seamlessly reduces to diffuse with zero scattering samples for sub-pixel scattering. We propose a novel joint-optimization algorithm for sample count and CV coefficient estimation. The main enabler is our novel time-variant covariance updating method that helps remove the effect of recent temporal dynamics from variance tracking. Since bandwidth is critical in real-time rendering, a solution without adding any extra textures is also provided.

#### News

• 2021.04.22: Live demo for detail visualization of, e.g., sample count & online CV coefficient during Posters and demos session (12:15am - 13:15am, PDT)
• 2021.04.21: I3D 2021 Day 1 Streaming Live (10:15am - 11:15am, PDT)

#### BibTex

@article{xie2021real,
title={Real-time Subsurface Control Variates: Temporally Stable Adaptive Sampling},
author={Xie, Tiantian and Olano, Marc},
journal={Proceedings of the ACM on Computer Graphics and Interactive Techniques},
volume={4},
number={1},
year={2021}
}


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© The Author(s) / ACM. This is the author’s version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in Proceedings of the ACM on Computer Graphics and Interactive Techniques, https://doi.org/10.1145/3451265