# Hole Concealment Algorithm Using Camera Parameters in Stereo 360 Virtual Reality System
## 4 Simulation Results
### Subjective Performance  
In order to check the performance of the proposed algorithm, we applied the proposed algorithm for the test sets of Brick Road, Alleyway, Tree, Bench, and Street. In Figure 9, VR images including the holes are compared with the concealed images, respectively. As shown in Figure 9, we can see that the proposed algorithm conceals the various holes effectively in the test images. Figure 9: ERP images including holes and the concealed regions, where the holes are concealed by the proposed algorithm. To compare the performances of various techniques subjectively, the pictures whose holes have been concealed by the methods are shown in Figure 11, where all of the pictures are a part of the left ERP picture and we made a hole artificially as Figure 10b in order to compare the concealed pictures Figure 11a-h with the reference image Figure 10a. As observed in Figure 11, the proposed algorithm outperforms the other techniques subjectively. In the picture Figure 11a result from Bertalmio [16], the pixels in the hole are filled by copying the neighboring pixels horizontally or vertically. Thus, the concealed region has artifact lines. When the method of Telea [17] is used to conceal the hole, each pixel in a hole is concealed progressively from the boundary to the center of the hole, where the value of the concealed pixel is set to the weighted sum of the values of the neighboring pixels. Thus, the concealed region of Figure 11b has smoothed and diffused distortion. In Figure 11c, when the method of Criminisi [18] is used, the pixels in the hole are filled by blocks, where the template matching algorithm is used. In this method, the SSD of template part is considered a cost function to estimate the most similar block, and the values of the pixels in the non-template part are not considered. Thus, some pixels in the  
Figure 11: Concealed images resulting from various algorithms for test set Mozart Hall: (**a**) Result from Bertalmio [16]; (**b**) Result from Telea [17]; (**c**) Result from Criminisi [18]; (**d**) Result from Liu [19]; (**e**) Result from Gilisoft Stamp Remover [33]; (**f**) Result from Theinpaint [34]; (**g**) Result from simple copy; (**h**) Result from proposed method. Figure 10: Example of reference picture and the original picture with an artificial hole for test set Mozart Hall: (**a**) Reference picture with no hole; (**b**) Original picture with a hole. hole are filled with wrong values. As shown in Figure 11d, the method of [PERSON] [19] based on deep learning has filled the hole with inappropriate blocks, which are generated from the deep learning engine. Figure 11e,f were resulted from Gilisoft stamp remover [33] and Theipaint [34], respectively. As shown in Figure 11e,f, these methods does not remove the holes completely. In Figure 11g, the hole in the left ERP is concealed just by copying a block in the right ERP, where the shapes and coordinates of the blocks, including the hole in the left ERP and the copied block in the right ERP, are same. As observed in Figure 11g, the concealed region has significant mismatches around the hole, because this method does not consider the disparity between the left and right views. Whereas the conventional techniques have serious artifacts in the concealed region, the image Figure 11h produced by the proposed algorithm has a natural and continuous boundary in the concealed region. Figures 12 and 13 show the simulation results for indoor pictures, where the size of the hole is bigger than that of Figures 10 and 11. As can be seen from Figures 12 and 13 and Figures 10 and 11, the performance tendencies of the various algorithms do not change even if the size of the hole is varied. Figure 14 shows the simulation results for the naturally generated holes that occurred non-artificially during the stitching procedure. Note that no reference picture was used in this test. In this configuration, both the left and right ERP images had holes at different locations independently.