Research On The Method Of Subsurface Scattering Material Rendering Of Heart For Virtual Surgery

With the rapid development of virtual reality(VR)and realistic rendering technologies,the realistic rendering of soft tissue in virtual surgery can provide better visual feedback and therapeutic effects for modern medicine.Owing to the complexity of the heart structure and the concealment of heart lesions,cardiovascular prevalence and mortality rates have remained high.The subsurface scattering rendering of the heart is the main root of cardiac lesions and realism.Therefore,one of the key points in the research of virtual surgery is enhancing the realistic sense of the subsurface scattering rendering of the heart.This paper carries out the study on the subsurface scattering rendering of the human heart.Firstly,the three-dimensional model of the heart is built accurately and the illumination model is set up for resolving the light casting onto the heart.Secondly,radiological integration algorithm is improved for the subsurface rendering of the heart on the basis of energy conservation.Finally,the realistic sense of the subsurface scattering rendering of the heart is improved based on the blending of the texture and screen space in the virtual surgery with post-processing so as to observe the lesions on the heart surface.The main work and research contents of this paper are described as following:(1)Heart illumination rendering framework is designed for virtual surgery.A three-dimensional reconstruction algorithm of the heart surface geometric model is used to create a three-dimensional model of the patient's heart,and the heart-related data is pre-processed.Designing the illumination model of the heart in the virtual surgery based on the analysis of current illumination models.Therefore,the method of subsurface scattering rendering is proposed in accord with the heart illumination effect and the overall rendering frame of this paper is elaborated.(2)The heart illumination model is built and calculated.Based on characteristics of the illumination in cardiac surgery scene and the analysis of the optical and subsurface physical structure of the heart,the traditional hierarchical models are used to set up the illumination model of the heart.Additionally,based on the law of conservation of energy,the incident light is classified and resolved into the diffuse reflection term,the specular highlight term and the subsurface scattering term separately,which can create a light effect that is consistent with the real heart.It can produce a better realistic heart rendering effect in the virtual surgery system with the light attenuation,shadow mapping and other post-processing technologies,in addition to the use of deferred rendering to accelerate the calculation of light.(3)The subsurface blend rendering of the heart is introduced to improve the effect.Based on the construction of the heart illumination model in the virtual surgery,we can not only use the texture coordinates as the coordinates of the rendering object and use the Gaussian function to convolve and simplify the operation,but also find the best approximation in the texture space(TS)in order to simulate the effect of subsurface scattering.In addition,the main problem of lacking inter region scattering caused by the excessive curvature of the texture space algorithm is eliminated by the blend rendering with the depth information and the mask processing of the screen space(SS).Furthermore,we improve the detail of the heart with parallax maps.Finally,the use of anti-aliasing,back culling as post-processing technologies performs better than ever before in the result of the subsurface scattering rendering of the heart.To conclude,the interactive experimental prototype system for rendering the subsurface scattering of the heart is designed and developed according to the illumination model proposed in this paper.The algorithm verification and visualization integration of each module are realized,and the experimental results and analysis are given.The experimental results show that the method proposed in this paper can well represent the light characteristics of heart material and meet the needs of virtual surgery,which plays a significant role in the realistic rendering of soft tissue.