# Fast 3D Content Update for Wide-Angle Holographic Near-Eye Display
## 7 Conclusions  
In this work, we propose a hologram update method for wide viewing angle holographic near-eye display, where the hologram plane is related to the eye position. Our solution addresses small viewpoint changes where two consecutive holograms have an overlapping region. The overlapping region is reused in the calculation framework of the updated hologram view. The update algorithm has two main components, which consist of transferring data from the overlapping regions and calculation of new information for the blank region. The transfer of overlapping regions is calculated by the classical AS method and approximate tilting, which is realized with an optimized frequency shift operation. It is worth noting that for the case of wide-angle holograms, this approximate tilt introduces minimal errors. New holographic information is introduced via the PAS method, which is an efficient tool for calculation of wide-angle CGH. The whole scheme enables significant acceleration, improving the calculation time of the final hologram. Numerical tests confirm the high accuracy of updated holograms for different sizes of overlap region. Moreover, it is shown that degradation of image quality over a large number of hologram update cycles is neglectable. Thus, the proposed method allows for quick generation of a sequence of wide-angle CGHs for continuous movement around 3D objects.  
Speed testing demonstrates that the computation time of this hologram update method is a linear function that mainly depends on the dimensions of the non-overlapping area, which must be newly computed using the PAS method. For example, for a 50% overlapping area size, the computation time is improved by a factor of two. Thus, the computations related to the overlapping area can be considered as negligible. The hologram update method is demonstrated for a display with an FoV of 62\({}^{\circ}\) and an average image size of  
Figure 10: The optical (**a,b**) and numerical (**c,d**) reconstruction of CGHs of [PERSON] statue, observed from the angle 340\({}^{\circ}\); (**e–h**) zooms of the sea dragon face.  
approximately one meter, and numerical and optical reconstructions where the continuous movement of an observer on an elliptical trajectory around an object are carried out. The employed object, a dense point cloud of 4 million points representing a statue of [PERSON], contains a large variety of features for each viewpoint. The obtained reconstructions of the 3D scene show that the proposed method provides continuous viewpoint change with high quality images, and is comparable with full frame CGH calculations.  
The following are available online at [[https://www.mdpi.com/article/10.3390/app12010293/s1](https://www.mdpi.com/article/10.3390/app12010293/s1)]([https://www.mdpi.com/article/10.3390/app12010293/s1](https://www.mdpi.com/article/10.3390/app12010293/s1)), Video S1: Optical reconstruction of the elliptical viewpoint movement around the Neptune. Video S2: Numerical reconstruction of the elliptical viewpoint movement around the Neptune.  
Conceptualization, T.K.; methodology, R.K.; software, R.K., J.M.-C. and T.K.; simulation, R.K.; experiment, M.C. and M.S.I.; visualization, R.K., M.C. and M.S.I.; supervision, T.K.; editing, all authors. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Science Centre, Poland grant number UMO-2018/31/B/ST7/02980 and Warsaw University of Technology.  
Not applicable.  
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon request.  
Not applicable.  
The authors declare no conflict of interest.