Interactive hair rendering and appearance editing under environment lighting

Abstract

Figure 1: Our algorithm achieves interactive hair rendering and appearance editing under environment lighting, including both single and multiple scattering effects. In this example, the user directly paints onto the hair to edit the spatially-varying scattering parameters. This results in a dynamic simulation of hair coloring. From left to right, the hair is dyed with a progressively more vivid color. The environment map is represented by 40 SRBF lights, and our algorithm runs at 8.3 fps on an NVIDIA GTX 580. AbstractWe present an interactive algorithm for hair rendering and appearance editing under complex environment lighting represented as spherical radial basis functions (SRBFs). Our main contribution is to derive a compact 1D circular Gaussian representation that can accurately model the hair scattering function introduced by [Marschner et al. 2003]. The primary benefit of this representation is that it enables us to evaluate, at run-time, closed-form integrals of the scattering function with each SRBF light, resulting in efficient computation of both single and multiple scatterings. In contrast to previous work, our algorithm computes the rendering integrals entirely on the fly and does not depend on expensive precomputation. Thus we allow the user to dynamically change the hair scattering parameters, which can vary spatially. Analyses show that our 1D circular Gaussian representation is both accurate and concise. In addition, our algorithm incorporates the eccentricity of the hair. We implement our algorithm on the GPU, achieving interactive hair rendering and simultaneous appearance editing under complex environment maps for the first time.

Modified filtered importance sampling for virtual spherical Gaussian lights

“…Spherical Gaussians [18,19] are often used for approximating the rendering of various types of materials under environment maps or area lights [20][21][22][23][24]. This is because they have closed-form solutions for the integral, product, and product integral, which are fundamental operations to evaluate rendering integrals.…”

Efficient Hair Rendering under Dynamic, Low-Frequency Environmental Light Using Spherical Harmonics

“…In Ren et al's method, the convolution of the SRBF light and the scattering function has been pre-computed as a lookup table. Later, Xu et al [5] derived a compact 1D circular Gaussian representation to model the scattering function and compute the rendering integral on the fly, thus eliminated the pre-computation of the convolution of the SRBF light and the scattering function. However, both methods use SRBFs to approximate the environmental light, so they cannot be applied to dynamic environment lighting.…”

“…Recently, real-time rendering of dynamic hair has become possible by approximating the environmental light with a set of spherical radial basis functions (SRBFs) [4], [5]. Since the number of SRBF lights is far fewer than the number of directional lights generated from directly sampling, the SRBF-based methods are able to render the hair model more efficiently.…”

Anisotropic spherical Gaussians

“…Laurijssen et al [2010] presented a method for efficiently rendering indirect highlights by an SG-based approximation of BRDF lobes and an efficient algorithm to merge multiple SGs into one. Xu et al [2011] achieved interactive rendering of hairs with dynamic appearance by approximating hair scattering functions by circular Gaussian, which is a 1D variant of SG. De Rousiers et al [2012] achieved real-time rendering of rough refractions by approximating the Bidirectional Transmittance Distribution Function (BTDF) using SGs.…”

“…This approximation is reasonable since the exponential term of ASG often changes much faster than the smooth term, and has been adopted extensively by existing methods [Wang et al 2009;Xu et al 2011;Iwasaki et al 2012a].…”