Design And Implementation Of A Photorealistic Rendering System For Facial Skin Based On Hybrid Illumination Algorithm

The facial expression can best represent the characteristics of the character,and the optical properties of the facial skin are also one of them.How to use complex lighting algorithms to simulate the photorealistic effect of soft facial skin is a hot spot in the photorealistic rendering of graphics.With the popularity of applications such as Internet conferences and short video live broadcasts,people hope to show a more perfect virtual self under the lens of nonprofessional photography environments.The research of this topic can help people solve this problem,design and simulate the realistic lighting effect of virtual facial skin in various scene environments.In this paper,various illumination characteristics of facial skin are firstly studied,and a hybrid illumination algorithm is proposed for photorealistic rendering of facial skin.The hybrid illumination algorithm includes four main parts: environment illumination calculation,direct illumination calculation,subsurface scattering calculation and post-processing of illumination synthesis.The environment lighting calculation is implemented by the Image Based Lighting(IBL)algorithm,which requires pre-calculation to generate environment maps,including irradiance maps,pre-filtered maps and BRDF lookup maps.The direct lighting calculation uses the parallel light and spotlight to fit the shadow map,and uses the Percentage Closer Soft Shadows(PCSS)algorithm and the Percentage Closer Filtering(PCF)algorithm to achieve the soft shadow effect of the facial skin,the diffuse and specular reflected light of direct illumination are calculated by the Cook-Torrance BRDF model,and the transmitted illumination in the thin-layer area of face is calculated by a fast approximation method.The subsurface scattering calculation adopts the separable subsurface scattering algorithm based on screen space,and proposes a sampling kernel calculation method with different sampling numbers according to the number of pixels covered by the sampling kernel,which can optimize the calculation efficiency of subsurface scattering.Finally,the above lighting results are synthesized with the skybox to obtain the final rendering effect of facial skin.The other work of this paper is to design and implement a photorealistic rendering system for facial skin,which provides an interactive rendering display tool for hybrid lighting algorithms.This paper designs a general rendering framework based on Vulkan,and implements a photorealistic rendering system for facial skin under this framework.Finally,the experiment and analysis of the algorithm are carried out under this system.The results show that the hybrid illumination algorithm proposed in this paper can effectively simulate the photorealistic rendering of facial skin in various scene environments.