An extended depth-of-field projection method using a high-speed projector with a synchronized oscillating variable focus lens / 基于可变焦透镜和高速投影仪同步控制的的扩展景深投影系统

Summary/摘要

Prototype of the proposed system

An extended depth-of-field projection is needed for spatial augmented reality. However, conventional projectors are often designed with a small F/#, which causes a narrow depth-of-field.
扩展景深的投影技术在增强现实技术中有着极其重要的作用。然而，由于传统投影仪的光学设计限制，景深范围通常较浅，投影内容容易模糊。

This research presents a system consisting of a variable focus optical path and 1000-fps 8-bit high-speed projector. This system oscillates the focal length of the lens at high speed and synchronizes it with the projection. High speed performance contributes to project clear images even under the oscillated focal length and to realize all-in-focus projections on several targets at different depths.
本研究提案了一个结合高速液体透镜和高速投影仪的系统。系统通过将液体透镜和投影仪的动作频率进行同步整合，最终可即使在不同深度空间的物体，依然可同时进行高清晰的投影显示。

Results/实验结果

传统投影仪只能够在固定焦段进行对焦，如近处（a），远处（b）或者中距离（c）。而本提案的技术，可以在以上三个距离范围内同时投影清晰的对焦图像。
本实验动态投影范围是0.3至1.5米，另可根据光学设计进行修改。

Fig. 2. Comparison of the experimental results. (a), (b) Scenes focused only at the near and far positions, respectively. (c) Scene focused on the middle position. (d) Result of our work, which is focused on all focal planes. Projection range was 0.3-1.5 m.

通过1000fps高速相机与高速投影仪进行同步拍摄，确认上述实验效果图。图片序号表示所对应的焦平面序号。1和6分别表示最远与最近。b和f表示投影焦平面在向后变化（从远至近，投影仪为参考）和向前变化（从近到远，投影仪为参考）。图片表示两个切换序列，从近到远和从远到近，整体周期为12毫秒。对应图像的刷新率为166.7Hz。

Fig. 3. Image sequence of the projection confirmed by the synchronized 1000 fps camera. The marks on the images represent the focal plane number and direction. 1 and 6 represent the farthest and nearest planes, respectively. b and f represent that the focal length is changing in a backward direction (from far to near to the system) and forward direction (from near to far to the system). The picture shows two sweep procedures (one for backward and another for forward sweeping) in a projection range of12 ms. Therefore, the image refresh rate is 166.7 Hz.

Video/ 视频

下面的视频是通过1000帧/秒的高速相机同步拍摄，视频是以30帧/秒进行慢速播放。人眼是观察不到频闪现象，因为投影速度超过人类频闪感知极限。
在每一个单独的焦平面上，可观察到数字1至6在高速切换。同时在第三个焦平面上，投射完数字1至6之后，会额外投射旋转的“十”字。投射内容可根据需要定制修改。

Video 1. This video was captured by a 1000 fps camera, but played with slow motion at 30 fps. Normally, human cannot observe the flicker. In the video, different textures are projected. Numbers 1 to 6 are projected in each panel with different focal lengths. In the third panel, an additional customized animation of a “spinning cross” is projected, after numbers 1 to 6.

Reference/ 参考

1. Hongjin Xu, Lihui Wang, Satoshi Tabata, Yoshihiro Watanabe, and Masatoshi Ishikawa, Extended depth-of-field projection method using a high-speed projector with a synchronized oscillating variable-focus lens, Applied Optics, 60(13), pp. 3917-3924 (2021) [DOI: 10.1364/AO.419470]
2. Hongjin Xu, Lihui Wang, Satoshi Tabata, Yoshihiro Watanabe, and Masatoshi Ishikawa: An extended depth-of-field projection method using a high-speed projector with a synchronized oscillating variable focus lens, SPIE Photonics West 2020 (San Francisco, 2020.2.5)/Proceedings of SPIE Vol.11304 , Advances in Display Technologies X, 113040T (2020) [DOI: 10.1117/12.2542477]

---