Research On Realistic Fast Rendering Of Human Face

With the fast development of virtual reality technology, virtual humans have been widely applied in works of movie and cartoon, which enhances the expressive ability of entertainment works. For whole body of virtual humans, human face is the main carrier to convey one’s ideas or feelings, and is full of individuation part. Also face is the most complex region of human appearance features, so how to present physical optics and expressions characteristics of human face, and make human face more realistic, i.e. the subjective sense of reality, which is the key to success for application of virtual humans. Hence, in this dissertation, optical characteristics of human face skin is firstly researched and later shading model of skin is constructed, which can realize realistic fast rendering under the premise of keeping characteristics of human face true enough. The research of fast rendering method makes realistic virtual humans having truly practical value.In this dissertation, by combing methods and models of realistic rendering, and using GPU programmable rendering pipeline, we carry out some exploratory researches which cover from interactive rendering of realistic face, influence of environment lighting for human face to rendering of multi-character face and expressions animation. The main contributions of the dissertation are summarized as follows:In order to effectively simulate the realistic face, and understand the process and effect of rendering in different views, we create an interactive rendering platform of hu-man face based on texture space, which uses a physical diffuse reflection model based on micro-facet to approximate the diffuse reflection on human face, and adopts sums of Gauss blur and texture stretch correction to simulate subsurface scattering. Combining diffuse reflection with subsurface scattering, we obtain a realistic face. Using graphical interface function of OpenGL, the interactive rendering platform for human face is de-signed. The result shows that we can accurately simulate diffusion of light scattering and realistic skin color of face. Also we realize many interactive rendering, which greatly helps user control and design the digital character, and has a great practical value.As appearance of human face can be influenced by surrounding environment light-ing, we present a new rendering method for realistic face based on environment light-ing. Using high dynamic range environment map to effectively simulate the environment lighting, and spherical harmonic function to transform high dynamic range image and ge-ometric shading function, we transform the complex infinitesimal calculus of environment lighting into dot product operations in frequency domain and realize the shading compu-tation in the GPU fragment shader programm. Then we implement the linear transfor-mation for spherical harmonic coefficients and obtain a dynamic lighting effect to human face. The result shows that realistic effect of face under nature environment lighting can be given and soft shadow is obvious. The digital character can be naturally integrated into the surroundings, which meets the consistency of lighting.In some virtual scenes having multiple characters, we consider not only sense of reality for face but also real-time performance. In the dissertation, we present realistic rendering of multiple characters based on facial geometric features and level of details. Through modeling and pre-computation of facial curvature and bump features, we can approximate subsurface scattering and diffuse reflection, and acquire faster realistic ren-dering for human face. When some characters appear away from view in virtual scenes, using mesh simplification, we can reduce data of head and amount of calculation in order to render in real time. The result shows that we can obtain physical skin color of face and detailed features of face, and realize relatively low time complexity and little computation amount which is especially suitable for virtual scene having multiple characters.Using facial expression we can enhance sense of reality for human face, and avoid the rigid and cartoon of digital character. In the dissertation, we present a facial expression animation rendering based3D fast morphing target. Firstly we design method of3D fast morphing target based on linear interpolation. Then we obtain target expressions accord-ing to movement of facial features. Later we pre-compute the difference vector between target expression and neutral expression, and load difference vector into the video frame buffer once using parallel technique of GPU. Through realization of morphing action in the vertex shader and shading skin color in fragment shader, we acquire the realistic fast rendering of facial expression animation. The result shows that we can obtain facial ex-pressions which is in accord with physical color features of human. Detailed features and shadow effect are clearly obvious, and also process of action morphing is more nature and fluent which meets requirement of expression animation of realistic face.