A Rendering Approach For Heterogeneous Translucent Materials

Since heterogeneous translucent materials,such as natural jades and marble,are complex hybrids of different materials,it is difficult to set precise optical parameters for subsurface scattering model as the material really has.In this thesis,an inverse rendering approach is presented for heterogeneous translucent jade materials from a single input photograph.Given one photograph with an object of a certain heterogeneous translucent jade material,our approach can generate 3D material distribution,estimate heterogeneous optical parameters,and render images using Monte Carlo ray marching method.The optical parameters are not physically accurate,but the material in rendered image is visually similar to the material in the source photograph.The main contributions of this thesis include:1)An image based material distribution estimation method is presented.Firstly,the material distribution model is initialized using 3D Simplex Noise combined with Fractal Brownian Motion.Then,histogram matching method is used to set colors of noise data based on the histogram of input photograph.After histogram matching,the color pattern of the noise data looks similar to the photograph.2)An noise value based optical parameters initialization method,and an image histogram based optical parameters optimization method is designed in this thesis.In the initialization process,optical parameters can be mapped based on the color pattern matched noise values.The initialized optical parameters can be used to render an image that has a certain similarity to the input photograph.In the optical parameters optimization process,we compare histograms of rendering result and input photograph,then,we approximate optical parameters based on the compare result in order to in order to minimize the difference between rendering result and input photograph and make the material in rendered image look more similar to the material in input photograph.The volume data with optimal heterogeneous optical parameters is obtained in the last iteration,which can be used for rendering any geometry model in different lighting conditions and different perspectives.3)In order to verify the effectiveness of the algorithm,our method is tested using photographs of a variety of heterogeneous translucent jade objects.Experimental results show that heterogeneous translucent objects can be rendered precisely similar to the material in the photograph using our method.