Research On Shear-Warp Volume Rendering Algorithm

The main research of this thesis is 3D direct volume rendering of MRI. MR images are now widely used in many fields. Researching on 3D direct volume rendering of MRI has significance in practice.Shear-Warp algorithm is considered as the fastest software for 3D direct volume rendering. So this thesis mainly research on this algorithm.Firstly, this thesis has successfully changed the MR slice images whose format is bmp to an overall file whose format is den. This conversion makes the Shear-Warp algorithm more completely, because the slice images of MR are often saved as the format of bmp. But the input data of this Shear-Warp algorithm is a overall file with the format of den. So in this thesis we design a program to change the original slice data to a whole file, which can be used by the Shear-Warp algorithm as the input data directly.Secondly, for some reason this algorithm will lose some detailed information of the original volume data. This makes the final image is not very clear. In order to avoid losing depth information, this thesis proposes two methods to improve this algorithm.The first is to design a lookup table to look for the opacity of the voxels. In this table one voxel will have different opacity which is classified by different shear angle. That is to say the opacity of one voxel is not only based on itself but also contain the information of the voxel, which has relationship with it along the direction of sightline. When computing the opacity of one resampling point only needs to look up in this table according to current shear angle.Because the above-improved method is complicated, we designed another simple method to get the improved effect. In the original Shear-Warp algorithm, it uses bilinear interpolation to get the opacity of the resampling points. The new algorithm uses tri-linear interpolation to instead of bilinear interpolation, because this tri-linear interpolation can add depth information in the opacity of the resampling points. This simple improved method has gotten effective effect.Finally, this thesis has do some research about parallel volume rendering.