Improvements On SHEAR-WARP Algorithm

The main research of this thesis is on the Direct Volume Rendering (DVR) based on the CT volume data sets. According to the certain sampling and rendering rules, Direct Volume Rendering algorithm directly render the volume data to get an image. DVR is one of the most important techniques in the field of information visualization which is widely used in medical image, CAD/CAM prototyping, industrial design, oil and gas exploration, virtual reality and so on. So the research on DVR is very significant in academia and practice.Shear-warp algorithm has been recognized as the fastest software-based rendering method. This paper mainly does some research on two aspects of Shear-warp: the rendering quality and the rendering speed.In the rendering quality aspect, Shear-warp algorithm loss the quality of the image for improving rendering speed. The big view orientation angle will cause serious staircasing phenomenon in the final image when we render the volume data set by Shear-warp algorithm The primary cause is that the resampling distance is so long that violate the Nyquist theorem in the resampling process. So the resampling data are unable to restore the original data message. In this paper we brought a new method for removing the staircasing phenomenon. Based on the theory of interpolation and approximation, a quadratic curve is constructed from four ordinal original sampling points along the viewing orientation. A new resampling voxel is obtained from the quadratic curve. Then a new slice is constructed between two original neighboring slices so that the sampling precision can be improved. Based on the new sampling slices, staircasing phenomenon can be reduced in Shear-warp rendering. In the paper we will show the adding slices principle, the specific algorithm and the complexity analysis. Surely, what we do to improve the image quality will affect the rendering speed and consume more space. How to get the best effect of the algorithm is still our further research.In the rendering speed aspect, Shear-warp algorithm employed a clever volume and image encoding scheme, coupled with a simultaneous traversal of volume and image that skips opaque image regions and transparent voxels. This will speed up the rendering speed. Shear-warp is totally based on the data structures to do some improvements that have nothing to do with the hardware. But recently, as the multi-core processor is more and more popular, it becomes the main stream processor in common PC and notebook. The multi-core processor has incomparable advantages to single-core processor in the aspect of multi-processing and Parallel Computation. It's very necessary for the volume rendering algorithm to be optimized based on multi-core CPU. In this paper we use multi-thread and vectorization methods to accelerate the Shear-warp algorithm which make full use of the multi-core CPU Characteristics. That makes it possible for the Shear-warp algorithm to become moreand more popular.In this paper, we do some experiments on the improved Shear-warp algorithmwith CT volume data sets. The experiment results show the efficiency of the improvements on both rendering quality and rendering speed.