Research On Interactive Rendering Under Complex Lighting Conditions

The complexity of the light sources is one of the major factors that causes the heavy computation of photorealistic rendering.Since dealing with such type of light sources requires a hefty amount of computation and storage,most current graphics related ap-plications still use simpler light sources,such as point light,directional light,or the simple area light.Recently,with the explosive growth of computer power,especially the development of programmable GPU,as well as the thriving demand of higher pho-torealism of synthesized images,rendering with complex lighting conditions becomes a hot research topic.This paper places an emphasis on the real-time illuminating issues associated with complex lighting conditions.Three categories of lighting conditions are taken into account,namely multiple area lights,environment lights,and textured area lights.The major contributions of this paper are four folds according to the types of light sources:(1)One of the performance bottlenecks of traditional global illumination ap-proaches(e.g.ray tracing)is the computation of ray-object intersection.To allow iterative feedback of traditional global illumination approaches,we propose a fast and optimal kd-tree construction method for virtual scenes.By analyzing the SAH function of the scene,simulated annealing is adopted in searching for the optimal split plane.In this way,the construction of kd-tree is significantly accelerated,with little loss of quality.Additionally,to explore the performance of our method,we have paralleled it on many-core CPUs for further reduction of building time.(2)An efficient strategy to decrease the running time of Monte Carlo based ren-dering algorithms is by reducing the number of samples per pixel.Unfortunately,in-sufficient sample rate leads to highly visible noise in images.One effective way is im-age denoising that smoothes out noise by applying suitable filters in a post-processing stage.Though traditional filters can average away undesired noise values,they also blur the important geometric details.We present an adaptive smoothing approach for noise removal and feature preservation,based on bilateral filtering.One key point of our methodology is the choice of employing three additional scene feature variances as the guidance to achieve better filtering results.This auxiliary information can effi-ciently identifies the subtle geometric details such as tiny holes and shape corners on reflected surfaces.(3)For all-frequency environmental lighting,we propose to separate the original environmental lighting into low-frequency part and highlight part based on a rejection-based sampling method.Scenes lit under low-frequency lighting are approximated via spherical harmonics lighting,which reduces the complex spherical integral into a sim-ple dot product between SH coefficients.Highlight illumination effects are simulated by a small set of sampled virtual point light.Experimental results demonstrate that our method can be sun in real-time without precomputation.(4)For dynamic textured area light,we introduce a novel light type called VAL(virtual area light),based on the subdivision of the original planar emitter.Since the size of each subdivided tile is comparatively small,we are able to consider it intensity distribution uniform.Moreover,VALs have also comprised the spatial and directional information,which is critical for synthesizing near-field lighting effects.When illumi-nation on the GPU,three essential factors associated with each VAL should be taken into account.The final illuminating result is accumulated by the lighting of all the VALs attenuated by the visibility between each pair of shading point and VAL.Ulti-mately,Real-time performance is achieved with time-varying area lighting conditions.