Research On Design Methods Of Multi-Dimentional Transfer Funtion In Volume Rendering

Currently, volume rendering has become one of the important technical methods for three-dimensional data visualization.And it has been widely valued and used in scientific computing and engineering. Transfer function of volume rendering maps voxel value of volume data to the optical imaging parameters, which directly determines the three-dimensional reconstructed images'quality. But for a long time, the design problem of transfer function of volume rendering had never been satisfactorily resolved, which became the bottleneck of the development and application of volume rendering and has been the key technology and hot issue of volume rendering in recent years. Based on researching and analysising the current method of transfer function design of volume rendering, this thesis used clustering algorithm and extreme learning machine to guide and optimize the the process of transfer function design of volume rendering, which can make the design process intelligent and automatic. The main work of this paper is as follows:(1) This paper proposed a novel method of multi-dimensional transfer function design of volume rendering. Based on anglicizing the internal structure of volume data by the scalar and the gradient magnitude histogram, all the volume data was classified using K-means clustering algorithm. Then, the volume data belonging to different clustering was pseudo-color mapped for the transformation between volume data and color coding. The experimental results show that transfer function designed by the proposed method can reveal the internal structures of volume data. And our method has the advantages of simple algorithm,high computational efficiency and convenient operation.The reconstructed three-dimensional images are more fidelity and have higher quality.(2) Based on the depth analysis of the feasibility and effectiveness of using neural network in the field of transfer function of volume rendering, the paper proposed a new method of transfer function design of volume rendering based on extreme learning machine. The method applied extreme learning machine to transfer function design. First all the volume data was classified using extreme learning machine through a interaction user interface. Then, the classified volume data was mapped to different color and opacity.The experimental results show that transfer function designed by the proposed method can effectively separate the different substances,and the reconstructed three-dimensional images are relatively clear. Compared to BP neural network, the learning rate of our method has great increse.