## 8 Conclusions  
This paper proposes an artwork identification methodology for 360-degree images using three polyhedron-based rectilinear projections and the DSK. A polyhedron-based rectilinear projection is used to reduce the distortion caused by an equirectangular projected 360-degree image. After comparing the matched features before and after applying the polyhedron-based method, feature matching is improved from no matched results to at least three correct matches. We used octahedron-, dodecahedron-, and 32-hedron-based rectilinear projections to identify artwork for analyzing the effects of the size, direction, and number of polygons on artwork identification. After summarizing the experiments from the 23-, 32-, and 79-inch monitors that were located at three different distortion positions, we found that the dodecahedron-based method has the most improved precision, which indicates that there should be  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \multirow{2}{*}{**Features**} & \multicolumn{4}{c}{**Feature Extraction Time (s)**} & \multicolumn{4}{c}{**Feature Matching Time (s)**} \\ \cline{2-9}  & **O** & **D** & **SP** & **SH** & **O** & **D** & **SP** & **SH** \\ \hline SIFT & 1.192 & 1.256 & 1.561 & 2.225 & 0.027 & 0.029 & 0.049 & 0.061 \\ SURF & 0.941 & 0.975 & 1.125 & 1.630 & 0.002 & 0.003 & 0.002 & 0.002 \\ MSER & 1.026 & 1.050 & 1.161 & 1.689 & 0.002 & 0.002 & 0.001 & 0.001 \\ FAST & 0.926 & 0.958 & 1.108 & 1.597 & 0.004 & 0.003 & 0.002 & 0.002 \\ BRISK & 0.929 & 0.962 & 1.113 & 1.601 & 0.002 & 0.002 & 0.002 & 0.002 \\ HOG & 1.161 & 1.147 & 1.163 & 1.748 & 0.003 & 0.002 & 0.001 & 0.001 \\ FREAK & 0.925 & 0.958 & 1.109 & 1.595 & 0.002 & 0.002 & 0.002 & 0.002 \\ \hline \end{tabular}
\end{table}
Table 2: Feature extraction and matching times.  
Figure 18: Comparisons of before and after applying the DSK. (**a**) 79-octahedron; (**b**) 32-octahedron; (**c**) 23-octahedron; (**d**) 79-dodecahedron; (**e**) 32-dodecahedron; (**f**) 23-dodecahedron.  
neither too many nor too few polygons. The DSK further improved the identification precision for the artwork that was located in the highly distorted position. With DSK, we can distinguish false matches and correct misidentified results. For the SIFT features of the artwork displayed on the 79-inch monitor and located in the seriously distorted position, there was a 45% increase in precision after applying the dodecahedron-based method. After using DSK, there is an additional 15% improvement in precision.  
The proposed approach is useful for automatic artwork identification applications in 360-degree images and has an important role in object recognition for 360-degree images. In the future, we will extend our method to three-dimensional sculpture identification in 360-degree images.  
This research was supported by the Ministry of Culture, Sports and Tourism (MCST) and Korea Creative Content Agency (KOCCA) in the Culture Technology (CT) Research & Development Program 2016.  
Both authors contributed to the research work. Both authors designed the new method and planned the experiments. [PERSON] led and reviewed the research work. [PERSON] performed the experiments and wrote the paper.  
The authors declare no conflict of interest.