Research On Key Technique Of Ray Casting Volume Rendering Algorithm

Visualization in Scientific Computing is a new field which the developed countries put forward to in the late 80s' in the 20th century. It applies computer graphics and image processing technique to transform the data from the process of scientific computing into graphics or images which will be displayed on the screen.The core of Visualization in Scientific Computing is Visualization for three-dimensional data fields. Volume rendering technique is a rapidly developed visualization method of Visualization for three-dimensional data fields in recent years. As a classical algorithm, the principle of Ray Casting algorithm composite the final image by distributing an opacity value and a color value to each voxel. So it can make high quality image and reserve detail information of volume data to use Ray Casting algorithm. Ray Casting algorithm is particularly for such three-dimensional image whose rendering area is blur. So it has a widely use.In this thesis, the development of Visualization in Scientific Computing and volume Rendering technique is introduced first. It explains the classification of the volume rendering algorithm , the characteristic and the differences among the algorithms.The thesis illuminates the theory basis of volume rendering, including the characteristic of volume data, space transform, projection transform, three-dementional clipping etc, and the Optical Models for Volume Rendering.Ray Casting algorithm is implemented using C++, including the key technique such as classification, distributing opacity and color value to each voxel, resampling, composition etc. Adaptive ray termination method is used here to improve the speed.During the pipeline of volume rendering, the designing of transfer function has always been a bottleneck to make a high quality image. The improvement of transfer function is discussed here. Based on front-to-back compositing manner, a new kind of transfer functions is implemented here and the experiment results are given.Finally, a software system named experiment platform for ray casting is implemented. The feature of the system is realizing a control interface for some step of the algorithm so that the user can make such operation necessarily as composition selecting, resampling step length selecting, transfer function selecting, slice viewing, image resizing and viewing direction selecting. The system is universal to some of VOL volume data.