# Virtual View Synthesis Based on Asymmetric Bidirectional DIBR for 3D Video and Free Viewpoint Video
## 3 Experimental Results and Discussion
### Evaluation of Asymmetric Bidirectional Rendering  
In order to evaluate the efficiency of the proposed asymmetric bidirectional rendering approach, we use single-view rendering (SVR), bidirectional rendering (BR), and asymmetric bidirectional rendering (ABR) to synthesize the target view. The SVR uses the primary view as the reference view. Table 2 shows the size of the holes in the virtual image, which is measured by counting the number of holes' pixels. It can be seen that most of the holes can be filled with contents in the auxiliary image. Compared with the BR that completely warps two reference images, the proposed approach only warps the regions that are helpful for hole filling. Although the hole reduction by the proposed approach is generally less than the BR, the rendering efficiency can be significantly improved, and all the remaining holes would be filled in the postprocessing. For the Breakdancers sequence, the hole size in BR3 with a large baseline is larger than BR4. Due to the lower depth quality of this sequence, hole reduction performance of the proposed approach is not as good as that on Ballet. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Name** & **Resolution** & **Primary View** & **Auxiliary View** & **Target View** \\ \hline Ballet & \(1024\times 768\) & View4 & View2 & View3 \\ Ballet & \(1024\times 768\) & View6 & View4 & View5 \\ Breakdancers & \(1024\times 768\) & View5 & View1 & View3 \\ Breakdancers & \(1024\times 768\) & View5 & View3 & View4 \\ Dancer & \(1920\times 1088\) & View1 & View9 & View5 \\ Shark & \(1920\times 1088\) & View1 & View9 & View5 \\ Kendo & \(1024\times 768\) & View1 & View5 & View3 \\ Baby1 & \(1240\times 1110\) & View1 & View5 & View4 \\ Books & \(1390\times 1110\) & View1 & View5 & View4 \\ Art & \(1390\times 1110\) & View1 & View5 & View4 \\ Aloe & \(1282\times 1110\) & View1 & View5 & View4 \\ Reindeer & \(1342\times 1110\) & View1 & View5 & View4 \\ Lampshade1 & \(1300\times 1110\) & View1 & View5 & View4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters of data sets. Figure 9 shows the partial comparison result of three rendering methods. Disocclusions and OFRs can be significantly reduced by BR and ABR. Due to the added color correction and ghost removal, the subjective visual quality of the ABR appears better than that of the BR in some cases. By selectively warping the auxiliary image, some foreground content with the wrong depth value can be effectively prevented from being warped to the disocclusions. On this basis, we compute the rendering time of three methods and the comparison results are shown in Figure 10. As the still image data is a standard parallel configuration, the image coordinates of the same 3D point in different views only have differences in horizontal coordinates, so the computational complexity is lower and the rendering speed is faster than that of MVD sequences. The BR warps the whole two images and its rendering time is about twice that of SVR. In contrast, the proposed rendering approach can achieve 97% hole reduction compared with the BR and reduce the rendering time by 37% on average. This is because the proposed approach warps the entire primary image and the local contents of the auxiliary image, thereby improving the rendering efficiency.